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This paper aims to explore machine learning techniques for post‐processing high‐resolution Numerical Weather Prediction (NWP) products for the early detection of convection. Data from the Arome Ensemble Prediction System and satellite observations from the Rapidly Developing Thunderstorm (RDT) product by Météo‐France are used to train a recurrent neural network model to predict areas of total convection and moderate convection. The learning task is formulated as a binary classification problem using a long short‐term memory (LSTM) network architecture. Results from the LSTM model are compared with an object‐based probabilistic approach to forecast convection using metrics such as a receiver operating characteristics (ROC) curve, the Brier score and reliability. Results indicate that the LSTM model performs similarly to the object‐based probabilistic benchmark when classifying moderate convection areas and shows improved skill when classifying areas of total convective. Finally, the LSTM model results are presented within an air traffic management context to showcase the potential use of machine learning models within an operational application. [ABSTRACT FROM AUTHOR]

An idealized aquaplanet moist global atmospheric model with realistic radiative transfer but no clouds and no convective parameterization is found to possess multiple climate equilibria. When forced symmetrically about the equator, in some cases the Inter Tropical Convergence Zone (ITCZ) migrates to an off‐equatorial equilibrium position. Mechanism denial experiments prescribing relative humidity imply that radiation‐circulation coupling is essential to this instability. The cross‐equatorial asymmetry occurs only when the underlying slab ocean is sufficiently deep and the atmosphere's spectral dynamical core is sufficiently coarse (∼T170 or less with our control parameters). At higher resolutions, initializing with an asymmetric state indicates metastability with very slow (thousands of days) return to hemispheric symmetry. There is some sensitivity to the model timestep, which affects the time required to transition to the asymmetric state, with little effect on the equilibrium climate. The instability is enhanced when the planetary boundary layer scheme favors deeper layers or by a prescribed meridional heat transport away from the equator within the slab. The instability is not present when the model is run with a convective parameterization scheme commonly utilized in idealized moist models. We argue that the instability occurs when the asymmetric heating associated with a spontaneous ITCZ shift drives a circulation that rises poleward of the perturbed ITCZ. These results serve as a warning of the potential for instability and non‐uniqueness of climate that may complicate studies with idealized models of the tropical response to perturbations in forcing. Plain Language Summary: Much of the rainfall in the tropics occurs in the Intertropical Convergence Zones (ITCZs). These regions are associated with the convergence of surface winds, which produces the rising air required to feed the Hadley cells. The ITCZ location is known to be determined by the spatial distribution of atmospheric heating as the Hadley cells act to erase thermal imbalance within the tropics. With hemispherically symmetric heating, a symmetric equatorial ITCZ is expected. However, it is shown in this paper that changes in the ITCZ location affect the distribution of the radiative cooling of the atmosphere through changes in the water vapor distribution, which may make the equatorial ITCZ unstable under some circumstances. In this situation, two alternative climates with the ITCZ shifted into either one of the hemispheres exist. This instability may play an important role for understanding the distribution of tropical precipitation and the potential for the existence of multiple climates for the same set of external conditions. Key Points: The equatorial ITCZ can be destabilized by radiation‐circulation coupling in a hemispherically symmetric aquaplanet modelAs the ITCZ drifts off the equator two different asymmetric equilibria may exist under symmetric forcing and boundary conditionsA theory is proposed based on the energy flux equator sensitivity to the perturbed asymmetric heating when the ITCZ moves off the equator [ABSTRACT FROM AUTHOR]

We develop a doubly periodic version of the Simple Convection‐Permitting E3SM Atmosphere Model (SCREAM) to provide an efficient configuration for this global convection permitting model (GCPM), akin to a single column model often found in conventional general circulation models. The design details are explained, in addition to the extensive case library associated with the doubly periodic SCREAM (DP‐SCREAM) configuration. We demonstrate that doubly periodic cloud resolving models are useful tools to explore the horizontal resolution sensitivity of GCPMs, in addition to replicating biases seen in the global models. Using DP‐SCREAM, we show that SCREAM exhibits behaviors of a scale aware model as it is able to naturally partition between sub‐grid scale (SGS) and resolved vertical transport across the gray zone of turbulence. We show that SCREAM is reasonably scale insensitive when run at resolutions from 1 to 5 km, but can exhibit sensitivity, particularly for the shallow convective regime, when run at resolutions approaching that of large eddy simulations. We conclude that SGS parameterization improvements are likely needed to reduce this scale sensitivity. Plain Language Summary: Advances in computational resources have allowed climate simulations to be performed with very high resolution, which provides higher quality results. However, these simulations require a lot of time and computer resources to perform, which makes these models difficult to use for the common scientist. In this paper we develop a high‐resolution configuration which focuses on a specific point on the globe, enabling it to run fast and to use minimal computational resources. This allows users and developers to gauge how the model may perform before doing a computationally intensive global simulation. We show that this faster configuration is a useful tool to replicate problems that are found in the global model and is a valuable way to assess sensitivities of the model, particularly pertaining to choices made in its resolution. Key Points: Doubly periodic configurations represent an efficient framework to supplement global cloud resolving modelsShallow convection is sensitive to horizontal resolution in Simple Convection‐Permitting E3SM Atmosphere Model (SCREAM) but stratiform clouds are more robustSCREAM exhibits the behaviors of a scale aware model and can represent a range of cloud regimes [ABSTRACT FROM AUTHOR]

A unique investigation has been undertaken to analyze the heat transmission by convective and radiative mechanisms in a fully saturated penetrable fin of a longitudinal structure positioned on a leaning surface. This study introduces the fusion of the realms of Homotopy perturbation and Sumudu transform techniques to address a previously unexplored problem involving a moving fin with temperature‐dependent thermal conductivity. In prior research papers, the Homotopy Perturbation Sumudu Transform Method (HPSTM) was utilized to obtain analytical solutions for fins featuring temperature‐dependent thermal conductivity. However, in our current study, we employ the HPSTM to tackle a novel problem involving a moving porous fin. This fin exhibits temperature‐dependent thermal conductivity and is subjected to convection and radiation effects. Through a comparison with numerical results, the present study has validated the dependability of its findings. The dimensionless temperature profile has been investigated by studying its relationship with several parameters. Here we observed that when the Peclet number (Pe) $({Pe})$ is augmented by 400%, there is a corresponding 1.11% increase in thermal outline at the fin's extremity. Enhancing the value of radiation parameter Nr ${Nr}$ by 400% declines the temperature of the fin tip by 14.079%. This study encourages the application of the Homotopy perturbation Sumudu transform technique in more complex fin problems. [ABSTRACT FROM AUTHOR]

Convective aggregation is an important atmospheric phenomenon which frequently occurs in idealized models in radiative‐convective equilibrium (RCE), where the effects of land, rotation, sea surface temperature gradients, and the diurnal cycle are often removed. This aggregation is often triggered and maintained by self‐generated radiatively driven circulations, for which longwave feedbacks are essential. Many questions remain over how important the driving processes of aggregation in idealized models are in the real atmosphere. We approach this question by adding a continentally sized, idealized tropical rainforest island into an RCE model to investigate how land‐sea contrasts impact convective aggregation and its mechanisms. We show that convection preferentially forms over the island persistently in our simulation. This is forced by a large‐scale, thermally driven circulation. First, a sea‐breeze circulation is triggered by the land‐sea thermal contrast, driven by surface sensible heating. This sea‐breeze circulation triggers convection which then generates longwave heating anomalies. Through mechanism denial tests we find that removing the longwave feedbacks reduces the large‐scale effects of aggregation but does not prevent aggregation from occurring, and thus we highlight there must be another process aiding the aggregation of convection. We also show, by varying the island size, that the aggregated convective cluster appears to have a maximum spatial extent of O $\mathcal{O}$(10,000 km). These results highlight that the mechanisms of idealized aggregation remain relevant when land is included in the model, and therefore these mechanisms could help us understand convective organization in the real world. Plain Language Summary: Large tropical storm clouds can cluster together to form organized systems, which are associated with extreme precipitation within the cloudy region, and very dry conditions away from the cloudy region. These systems, called organized deep convection, are often studied in simplified models of the atmosphere where the land, Earth's rotation, and variations in sea‐surface temperature are removed. In this paper we take a step toward reality and look at how including a large, idealized island in a simplified model affects how convection clusters. We show that convective clouds group together over the land throughout our model simulations. We investigate the processes driving this and find that surface flux feedbacks dominate early in the simulations. The feedbacks maintaining the convective aggregation are more complex. We find there is an important role for the longwave feedbacks, but that there must be another necessary process also aiding the clustering process. Our results highlight that the processes in highly idealized modeling studies seem to be relevant in more realistic models, and thus could help us understand how convection organizes in the real world. However, we also conclude it is important that follow‐up work investigates the remaining additional feedbacks to gain a more complete understanding. Key Points: Convection preferentially aggregates over land in a global radiative‐convective equilibrium simulationA global land‐centered circulation drives the aggregation and is triggered through surface fluxes, but maintained through longwave fluxesThe land‐based convective cluster appears to have a maximum spatial scale of O $\mathcal{O}$(10,000 km) [ABSTRACT FROM AUTHOR]

Tropical convection is expected to decrease with warming, in a variety of ways. Specific incarnations of this idea include the "stability‐iris" hypothesis of decreasing anvil cloud coverage, as well as the decrease of both tropospheric and cloud‐base mass fluxes with warming. This paper seeks to encapsulate these phenomena into three "rules," and to explore their interrelationships and robustness, using both analytical reasoning as well as cloud‐resolving and global climate simulations. We find that each of these rules can be derived analytically from the usual expression for clear‐sky subsidence, so they all embody the same essential physics. But, these rules do not all provide the same degree of constraint: the stability‐iris effect is not entirely robust due to unconstrained microphysical degrees of freedom, and the decrease in cloud‐base mass flux is not entirely robust due to unconstrained effects of entrainment and detrainment. Tropospheric mass fluxes on the other hand are shown to be well‐constrained theoretically, and when evaluated in temperature coordinates they exhibit a monotonic decrease with warming at all vertical levels and across a hierarchy of models. Plain Language Summary: Tropical convection and high cloudiness are expected to decrease with global warming, in a variety of ways. This phenomenon has a few different manifestations in the literature, whose relationships are unclear. We show analytically that these explanations all embody the same essential physics, but are not equally robust and thus do not all have the same predictive power. Key Points: Three constraints on tropical convection can all be derived analytically from clear‐sky subsidenceTropospheric mass fluxes at a fixed isotherm should robustly decrease under global warmingDecreases in anvil cloud area and cloud‐base mass flux are not as robust [ABSTRACT FROM AUTHOR]

Laplace transforms were used in this paper to obtain analytical solutions for the axisymmetric problem under a constant well temperature using the convective heat transfer boundary condition, which included the conduction and convection in the aquifer as well as heat exchange at the boundary. This solution curve intuitively illustrates the temperature distribution within the aquifer. The effects of various parameters on this analytical solution were analyzed. According to this parametric analysis there exists a quasi‐steady‐state of temperature distribution in the axisymmetrical situation, which is different from the planar symmetry problem. In addition, the thermal breakthrough increases with the injected rate and decreases with the increasing convective heat transfer coefficient. Our analytical solution matched the results yielded by the numerical simulation quite well. [ABSTRACT FROM AUTHOR]

Deep learning can accurately represent sub‐grid‐scale convective processes in climate models, learning from high resolution simulations. However, deep learning methods usually lack interpretability due to large internal dimensionality, resulting in reduced trustworthiness in these methods. Here, we use Variational Encoder Decoder structures (VED), a non‐linear dimensionality reduction technique, to learn and understand convective processes in an aquaplanet superparameterized climate model simulation, where deep convective processes are simulated explicitly. We show that similar to previous deep learning studies based on feed‐forward neural nets, the VED is capable of learning and accurately reproducing convective processes. In contrast to past work, we show this can be achieved by compressing the original information into only five latent nodes. As a result, the VED can be used to understand convective processes and delineate modes of convection through the exploration of its latent dimensions. A close investigation of the latent space enables the identification of different convective regimes: (a) stable conditions are clearly distinguished from deep convection with low outgoing longwave radiation and strong precipitation; (b) high optically thin cirrus‐like clouds are separated from low optically thick cumulus clouds; and (c) shallow convective processes are associated with large‐scale moisture content and surface diabatic heating. Our results demonstrate that VEDs can accurately represent convective processes in climate models, while enabling interpretability and better understanding of sub‐grid‐scale physical processes, paving the way to increasingly interpretable machine learning parameterizations with promising generative properties. Plain Language Summary: Deep neural nets are hard to interpret due to their hundred thousand or million trainable parameters without further postprocessing. We demonstrate in this paper the usefulness of a network type that is designed to drastically reduce this high dimensional information in a lower‐dimensional space to enhance the interpretability of predictions compared to regular deep neural nets. Our approach is, on the one hand, able to reproduce small‐scale cloud related processes in the atmosphere learned from a physical model that simulates these processes skillfully. On the other hand, our network allows us to identify key features of different cloud types in the lower‐dimensional space. Additionally, the lower‐order manifold separates tropical samples from polar ones with a remarkable skill. Overall, our approach has the potential to boost our understanding of various complex processes in Earth System science. Key Points: A Variational Encoder Decoder (VED) can predict sub‐grid‐scale thermodynamics from the coarse‐scale climate stateThe VED's latent space can distinguish convective regimes, including shallow/deep/no convectionThe VED's latent space reveals the main sources of convective predictability at different latitudes [ABSTRACT FROM AUTHOR]

Recent observational and numerical studies have investigated the dynamics of fine‐scale gravity waves radiating horizontally outward from tropical cyclones. The waves are wrapped into spirals by the tangential wind of the cyclone and are described as spiral gravity waves. This study addresses how well numerical simulations of these waves compare to observations as the horizontal grid spacing is decreased from 2.0 to 1.0 to 0.5 km, and the number of vertical levels changes from 25 to 50 to 100. Spectral filtering is applied to separate the fine‐scale waves in vertical velocity (w) and the larger‐scale waves in pressure (p) from moist updrafts and downdrafts in the eyewall and rainbands. As the grid spacing decreases, the radial wavelengths of the w waves decrease from 20 to 7 km, approaching observed values. For grid spacing 1.0 km, the p waves become well‐resolved with wavelength 70 km. The outward phase speeds range from 15 to 30 ms−1 for the w waves and 50 to 70 ms−1 for p waves. Analysis of the upper‐level outflow region finds that the spiral w waves propagate 5–10 ms−1 faster due to radial advection, but also finds what appear to be different classes of larger‐amplitude, slow‐moving spiral waves. Similar waves can be seen in satellite images, which appear to be caused by dynamical instability of the strongly vertically sheared radial and tangential winds in the TC outflow. Plain Language Summary: Tropical cyclones—known also as hurricanes, typhoons, and cyclones—cause some of the most significant weather impacts around the world. Recent work has found that these storms causes oscillations in the atmosphere that radiate outward in expanding spirals. These are called spiral gravity waves. This paper investigates how well computer models reproduce these waves as the pixel sizes used by the model become smaller (requiring more computer power). As the pixels decrease to 1.0 km or less, the waves become increasingly realistic. The simulations show two types of spiral gravity waves, which can be seen either in vertical motion or in the atmospheric pressure field. The vertical motion waves are 5–10 km wide and move outward at 90 km hr−1, while the pressure waves are 60–80 km wide and move outward at 220 km hr−1. Focusing on the cloud shield at the top of the cyclone (what we see in satellites) reveals a new class of slow‐moving, spiral waves that are distinct from the gravity waves. Key Points: Computer simulations of tropical cyclones show the detailed structures of outward propagating spiral gravity wavesAs resolution increases, the wave properties come close to, but do not converge to observed valuesA new class of waves is identified in the upper‐level outflow, which are slow‐moving spiral waves due to dynamical instabilities [ABSTRACT FROM AUTHOR]

Equatorial waves (EWs) are synoptic‐ to planetary‐scale propagating disturbances at low latitudes with periods from a few days to several weeks. Here, this term includes Kelvin waves, equatorial Rossby waves, mixed Rossby–gravity waves, and inertio‐gravity waves, which are well described by linear wave theory, but it also other tropical disturbances such as easterly waves and the intraseasonal Madden–Julian Oscillation with more complex dynamics. EWs can couple with deep convection, leading to a substantial modulation of clouds and rainfall. EWs are amongst the dynamic features of the troposphere with the longest intrinsic predictability, and models are beginning to forecast them with an exploitable level of skill. Most of the methods developed to identify and objectively isolate EWs in observations and model fields rely on (or at least refer to) the adiabatic, frictionless linearized primitive equations on the sphere or the shallow‐water system on the equatorial β$$ \beta $$‐plane. Common ingredients to these methods are zonal wave‐number–frequency filtering (Fourier or wavelet) and/or projections onto predefined empirical or theoretical dynamical patterns. This paper gives an overview of six different methods to isolate EWs and their structures, discusses the underlying assumptions, evaluates the applicability to different problems, and provides a systematic comparison based on a case study (February 20–May 20, 2009) and a climatological analysis (2001–2018). In addition, the influence of different input fields (e.g., winds, geopotential, outgoing long‐wave radiation, rainfall) is investigated. Based on the results, we generally recommend employing a combination of wave‐number–frequency filtering and spatial‐projection methods (and of different input fields) to check for robustness of the identified signal. In cases of disagreement, one needs to carefully investigate which assumptions made for the individual methods are most probably not fulfilled. This will help in choosing an approach optimally suited to a given problem at hand and avoid misinterpretation of the results. [ABSTRACT FROM AUTHOR]

Infrared brightness temperature and tropical cyclone (TC) data from 2000 to 2018 were used to investigate the relationships between the radius of maximum wind (RMW), radius of gale‐force winds (34 kt or 17 m/s; R34), and intensity for intensifying and expanding North Atlantic TCs. Different relationships between intensity and R34 were found for different RMWs. Very deep convective clouds with infrared brightness temperatures ≤208 K are mainly observed on the outer edge of the RMW when it is stable. In such a case, the TC intensifies and R34 expands rapidly when very deep convective clouds occur in both the inner and outer regions, and thus a linear relationship between the intensity and R34 occurs when the RMW is stable. Plain Language Summary: Previous studies have shown that the inner‐core size, usually defined as radius of maximum wind (RMW), is considered to be correlated with subsequent intensity changes closely, while the outer region size, usually defined as radius of gale‐force winds (34 kt or 17 m/s, R34), is found to be weakly correlated with intensity and intensity change of tropical cyclones (TCs). The changes of azimuthal‐mean tangential wind speed in the inner and outer regions are considered to be independent of each other. This study reveals a significant linear relationship between intensity and R34 when RMW is steady in North Atlantic TCs from 2000 to 2018. The constant RMW roughly responds to the stability of the convective heating distribution. Consequently, with more convection heating, TCs intensify more rapidly and R34 expands faster. The results in this paper may provide a new perspective for understanding the relationship between TC intensity and size. Key Points: Tropical cyclone (TC) intensity and radius of gale‐force wind (R34) are linearly related when the radius of maximum wind (RMW) is stableLinear relationships between TC intensity and R34 are different for different initial RMWTCs intensify more rapidly and R34 expands faster with more very deep convective clouds with a stable RMW [ABSTRACT FROM AUTHOR]

Accurately representing mesoscale convective systems (MCSs) is crucial to simulating the energy and water cycles in global climate models. Using a novel MCS identification and tracking algorithm applied to observations and model simulations, we evaluate how well the Energy Exascale Earth System Model (E3SM) simulates MCSs over the central US. Simulations performed by E3SM at 25 km grid spacing with and without superparameterization (SP) are compared and evaluated against observations using multiple metrics highlighting important MCS characteristics. Compared to E3SM, the superparameterized model (SP‐E3SM) better simulates MCS number and MCS precipitation amount, diurnal cycle, propagation, and the probability distribution of precipitation rate in both spring and summer. The improvement from SP is partly contributed by improvement in simulating the large‐scale environments, featuring enhanced atmospheric low‐level moisture and larger moisture transport to the central US relative to E3SM. However, SP‐E3SM still underestimates MCS precipitation amount, particularly in summer. This underestimation is closely related to the negative bias in MCS precipitation intensity, although the drier environments simulated during summer also contributes to underestimation of MCS frequency. Without SP, the larger bias in MCS precipitation amount is closely related to the negative bias in MCS frequency, while the substantial dry bias in the large‐scale environments also contributes to underestimation of MCS intensity. Our results suggest that SP improves MCS simulation by improving modeling of the large‐scale environments and convection initiation, which are both major limiting factors in E3SM even at 25 km grid spacing where deep convection is represented by a cumulus parameterization. Plain Language Summary: Large thunderstorms called mesoscale convective systems (MCSs) are an important source of flood‐producing rainfalls. In this paper, we examine how well the Energy Exascale Earth System Model (E3SM) simulate MCSs over the central US in spring and summer by comparing against observations. We run two versions of E3SM: one is the standard E3SM that uses a traditional parameterization to simulate deep convection, the other is E3SM with a superparameterization (SP‐E3SM) that uses a cloud resolving model within each E3SM grid column to explicitly simulate deep convection. By using a novel detection and tracking algorithm to characterize MCS features, we find that SP‐E3SM can better simulate the number, rainfall amount and intensity, and the diurnal cycle of MCSs compared to E3SM. SP improves MCS simulations by improving the representation of the large‐scale circulations and convection initiation. Despite the improvement, SP‐E3SM still underestimates the MCS rainfall amount, which is largely related to the underestimation of MCS rainfall intensity. In contrast, the larger underestimation of rainfall amount in E3SM is attributed in large parts to the lower MCS frequency. This study highlights the importance of large‐scale moisture transport and convection initiation in simulating MCSs. Key Points: Mesoscale convective systems (MCSs) in E3SM at 25 km with and without superparameterization (SP) are evaluated the central USIncluding SP significantly improves MCS simulations in both spring and summer, although large dry biases are still apparent in summerImprovements from SP are contributed by improved simulations of the large‐scale environments and MCS number and precipitation frequency [ABSTRACT FROM AUTHOR]

Multi‐fluid models have recently been proposed as an approach to improving the representation of convection in weather and climate models. This is an attractive framework as it is fundamentally dynamical, removing some of the assumptions of mass‐flux convection schemes which are invalid at current model resolutions. However, it is still not understood how best to close the multi‐fluid equations for atmospheric convection. In this paper we develop a simple two‐fluid, single‐column model with one rising and one falling fluid. No further modelling of sub‐filter variability is included. We then apply this model to Rayleigh–Bénard convection, showing that, with minimal closures, the correct scaling of the heat flux (Nu) is predicted over six orders of magnitude of buoyancy forcing (Ra). This suggests that even a very simple two‐fluid model can accurately capture the dominant coherent overturning structures of convection. [ABSTRACT FROM AUTHOR]

A new technique has been developed to determine the high‐latitude electric potential from observed field‐aligned currents (FACs) and modeled ionospheric conductances. FACs are observed by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE), while the conductances are modeled by Sami3 is Also a Model of the Ionosphere (SAMI3). This is a development of the Magnetosphere‐Ionosphere Coupling approach first demonstrated by Merkin and Lyon (2010), https://doi.org/10.1029/2010ja015461. An advantage of using SAMI3 is that the model can be used to predict total electron content (TEC), based on the AMPERE‐derived potential solutions. 23 May 2014 is chosen as a case study to assess the new technique for a moderately disturbed case (min Dst: −36 nT, max AE: 909 nT) with good GPS data coverage. The new AMPERE/SAMI3 solutions are compared against independent GPS‐based TEC observations from the Multi‐Instrument Data Analysis Software (MIDAS) by Mitchell and Spencer (2003), and against Defense Meteorological Satellite Program (DMSP) ion drift data. The comparison shows excellent agreement between the location of the tongue of ionization in the MIDAS GPS data and the AMPERE/SAMI3 potential pattern, and good overall agreement with DMSP drifts. SAMI3 predictions of high‐latitude TEC are much improved when using the AMPERE‐derived potential as compared to Weimer's (2005), https://doi.org/10.1029/2005ja011270 model. The two potential models have substantial differences, with Weimer producing an average 77 kV cross‐cap potential versus 60 kV for the AMPERE‐derived potential. The results indicate that the 66‐satellite Iridium constellation provides sufficient resolution of FACs to estimate large‐scale ionospheric convection as it impacts TEC. Plain Language Summary: Plasma in the ionosphere convects across high latitudes in response to electric fields generated by solar wind driving of Earth's magnetosphere. Magnetic data from the 66‐satellite Iridium satellite constellation is routinely analyzed to measure the electric currents flowing between the ionosphere and magnetosphere. In this paper, we combined these observed field‐aligned currents with a model of the ionospheric conductance to estimate the corresponding electric field in the ionosphere. We used these electric field estimates to specify the plasma convection in a first‐principles ionosphere model, and compared the results against independent data in a moderately disturbed period. The results of our case study indicate that the technique works well, although plasma convection is not the only factor that causes uncertainty into predictions of the high‐latitude ionosphere. The data used here can be made available in near‐real‐time, so it is possible that our technique could be adopted for operational space weather prediction. Key Points: Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) field‐aligned currents have been combined with the Sami3 is Also a Model of the Ionosphere (SAMI3) model to estimate the high‐latitude potentialIndependent validation of the new technique using satellite drifts and ground‐based total electron content indicates good agreement overallThe SAMI3 model performs better in this case when using AMPERE‐derived potentials than when using the empirical Weimer potential [ABSTRACT FROM AUTHOR]

Characteristics of, and fundamental differences between, the radiative‐convective equilibrium (RCE) climate states following the Radiative‐Convective Equilibrium Model Intercomparison Project (RCEMIP) protocols in the Community Atmosphere Model version 5 (CAM5) and version 6 (CAM6) are presented. This paper explores the characteristics of clouds, moisture, precipitation and circulation in the RCE state, as well as the tropical response to surface warming, in CAM5 and CAM6 with different parameterizations. Overall, CAM5 simulates higher precipitation rates that result in larger global average precipitation, despite lower outgoing longwave radiation compared to CAM6. Differences in the structure of clouds, particularly the amount and vertical location of cloud liquid, exist between the CAM versions and can, in part, be related to distinct representations of shallow convection and boundary layer processes. Both CAM5 and CAM6 simulate similar peaks in cloud fraction, relative humidity, and cloud ice, linked to the usage of a similar deep convection parameterization. These anvil clouds rise and decrease in extent in response to surface warming. More generally, extreme precipitation, aggregation of convection, and climate sensitivity increase with warming in both CAM5 and CAM6. This analysis provides a benchmark for future studies that explore clouds, convection, and climate in CAM with the RCEMIP protocols now available in the Community Earth System Model. These results are discussed within the context of realistic climate simulations using CAM5 and CAM6, highlighting the usefulness of a hierarchical modeling approach to understanding model and parameterization sensitivities to inform model development efforts. Plain Language Summary: Clouds, circulations and rainfall in the tropics play an important role in Earth's climate. However, global climate models differ in their representation of these features, contributing to uncertainty in future climate projections. One useful tool to better understand model differences and inform efforts to improve models is to analyze idealized configurations. We explore two different numerical representations of an idealized atmosphere relevant to tropical regions to determine the impact on the characteristics of clouds, rainfall and circulations as well as the tropical atmospheric response to warming. We show that our idealized models mirror differences in the low‐cloud structure in the deep tropics of more realistic models. This work also finds similarities between the two numerical representations, such as a decrease in the spatial extent of high altitude clouds with warming. As the surface is warmed, both versions also show increases in the clustering of clouds, the likelihood of extreme precipitation rates, and an estimate of how much warming would occur in response to a doubling of carbon dioxide. Key Points: A new radiative‐convective equilibrium (RCE) configuration is added to the official release of Community Earth System Model (CESM) to facilitate the use of Radiative‐Convective Equilibrium Model Intercomparison Project (RCEMIP) in the CESM hierarchyThe Community Atmosphere Model version 5 and Community Atmosphere Model version 6 (CAM6) RCEMIP climate states and variation across SST experiments are documented in the context of the CESM hierarchyDiffering parameterizations lead to a reduction of low‐level clouds in CAM6, consistent with differences in more realistic simulations [ABSTRACT FROM AUTHOR]

This study investigates how wind shear and momentum fluxes in the surface‐ and boundary layer vary across wind and cloud regimes. We use a 9‐year‐long data set from the Cabauw observatory complemented by (8.2 × 8.2 km2) daily Large Eddy Simulation (LES) hindcasts. An automated algorithm classifies observed and simulated days into different cloud regimes: (a) clear‐sky days, (b) days with shallow convective clouds rooted in the surface layer, with two ranges of cloud cover, and (c) non‐convective cloud days. Categorized days in observations and LES do not always match, particularly the number of non‐convective cloud days are underestimated in the LES, which likes to develop convection. However, the climatology and diurnal cycle of winds for each regime are very similar in LES and observations, strengthening our confidence in LES' skill to reproduce certain clouds for certain atmospheric states. Along‐wind momentum flux profiles are similar across all regimes, but large cloud cover (convective and non‐convective) days have larger total momentum flux distributed over a deeper layer, with up to 30% of the surface flux still present near cloud base. The clear‐sky and especially shallow cumulus regime with low cloud cover have notably larger crosswind momentum fluxes in the boundary layer. Surface‐layer wind shear at daytime is smallest in the shallow cumulus regimes, having deeper boundary layers and a steady increase in surface layer wind speed during daytime. Compared to clear‐sky days at a similar stability, convective cloud regimes have smaller surface‐layer wind shear and larger surface friction than estimated by Monin‐Obukhov Similarity Theory. Plain Language Summary: Accurate modeling of surface wind speeds is required to improve wind energy prediction and representation of surface fluxes in models, as they influence a range of atmospheric processes. This paper compares the surface layer wind gradients and turbulent momentum fluxes among various wind and cloud regimes. We use observed and modeled climatological wind and cloud records over the Netherlands, which we grouped into (a) clear‐sky days, (b) (cumulus) clouds that interact with the layer below, with two ranges of cloud cover, and (c) days not driven by convection. We have confidence in the modeled winds and clouds: when comparing the regime‐averaged behavior of wind, temperature, and humidity; the model and observations show similar results. When comparing the different cloud regimes, we find more similar wind speeds at different altitudes on cumulus days. Shallow cumulus regimes appear to have larger surface friction than clear‐sky regimes when correcting for atmospheric stability. Key Points: Cloudy regimes have larger total momentum flux distributed over a deeper layer, with up to 30% of the surface flux present near the cloud baseClear‐sky and shallow cumulus regimes have notably larger crosswind momentum fluxes in the boundary layerConvective cloud regimes have less surface layer wind shear than the clear‐sky regime for a given surface layer [ABSTRACT FROM AUTHOR]

The arc aurora can be considered as the visualization of the field‐aligned current (FAC). In various cases, the numerically reproduced FAC morphologically matches well with that of the observed arc aurora. Such example can be seen in the sun‐aligned arc, the fan arc, and the theta aurora under the northward interplanetary magnetic field (IMF), and the substorm, the quiet arc, and the initial brightening under the southward IMF. The FAC reproduced by the global simulation is based on the general principle of the magnetohydrodynamic (MHD). In such general principle, the FAC is transmission of net charge, net charge is divE, and E is equivalent to motion. After all, the FAC is transmission of convection motion. In order to transmit the FAC to the dissipative ionosphere based on the MHD, formations of the dynamo and shear that leads from the magnetosphere to the ionosphere are essential. The dynamo and shear are reproduced so as to properly match with each convection structure. The comparison under various magnetospheric topologies between the global simulation and the arc aurora observation indicates that the arc aurora and the FAC occurs inevitably controlled by convection structure. Such a principle of the FAC and convection holds even for the onset FAC. Key Points: Under any magnetospheric topologies, shear structure brings about morphologies of the field‐aligned current (FAC) and arc aurorasThe FAC occurs with the dynamo and shear following the MHD principle, and transmits convection from the magnetosphere to the ionosphereThe substorm CW that forms without considering the dynamo and shear is not reproduced in the global simulation [ABSTRACT FROM AUTHOR]

We simulate the Madden‐Julian oscillation (MJO) over an aquaplanet with uniform surface temperature using the multiscale modeling framework (MMF) configuration of the Energy Exascale Earth System Model (E3SM‐MMF). The model produces MJO‐like features that have a similar spatial structure and propagation behavior to the observed MJO. To explore the processes involved in the propagation and maintenance of these MJO‐like features, we perform a vertically resolved moist static energy (MSE) analysis for the MJO (Yao et al., 2022, https://doi.org/10.1175/jas‐d‐20‐0254.1). Unlike the column‐integrated MSE analysis, our method emphasizes the local production of MSE variance and quantifies how individual physical processes amplify and propagate the MJO's characteristic vertical structure. We find that radiation, convection, and boundary layer (BL) processes all contribute to maintaining the MJO, balanced by the large‐scale MSE transport. Furthermore, large‐scale dynamics, convection, and BL processes all contribute to the propagation of the MJO, while radiation slows the propagation. Additionally, we perform mechanism‐denial experiments to examine the role of radiation and associated feedbacks in simulating the MJO. We find that the MJO can still self‐emerge and maintain its characteristic structures without radiative feedbacks. This study highlights the role of convective MSE transport in the MJO dynamics, which was overlooked in the column‐integrated MSE analysis. Plain Language Summary: We conduct simulations of the Madden‐Julian oscillation (MJO) using a computer model that can explicitly simulate deep convective clouds. The simulated MJO behaves similarly to what has been observed in the real world in terms of its spatial structure and propagation. We then delve into the detailed mechanisms behind the MJO, using a method that analyzes how energy and moisture move vertically through the atmosphere, rather than just averaging these properties across the whole atmosphere. This novel analysis shows that radiation, convection, turbulence in the atmospheric boundary layer, and large‐scale atmospheric flows all play roles in sustaining the MJO and affect its eastward propagation. Interestingly, the MJO can still develop and maintain its unique features without the influence of radiation, indicating other processes are also key. This research underscores the importance of understanding the vertical transport of energy and moisture by convective storms in studying the MJO, an aspect previously underappreciated in some simpler models and diagnoses. Key Points: We have successfully simulated the Madden‐Julian Oscillation (MJO) using the Energy Exascale Earth System Model‐multiscale modeling framework over an aquaplanet with uniform surface temperatureVertically resolved analyses of moist static energy highlight the role of convection in the maintenance and propagation of the MJOMechanism‐denial experiments show that radiative feedbacks are not essential to simulate the MJO [ABSTRACT FROM AUTHOR]

Mesoscale convective systems (MCSs) that occur in the Baiu frontal zone (BFZ) can cause devastating flash floods during early summer in Japan; however, the environmental conditions necessary for their development require further investigation. High‐frequency atmospheric soundings, conducted using multiple marine vessels in the East China Sea on 19 June 2022, captured the detailed environmental conditions pertaining to the development of an MCS within the BFZ. The MCS, which developed rapidly without any remarkable preceding synoptic or mesoscale disturbance in the mid‐ or upper troposphere, caused intense precipitation exceeding 80 mm/hr. The MCS persisted for approximately 6 hr, and it intensified when the influx of nearly saturated air near the sea surface toward a weak surface front overlapped with the influx of free‐tropospheric moist air. The influx of nearly saturated air near the sea surface ensured conditional instability within the lower troposphere. The influx of moist air in the free troposphere contributed to the near‐saturation conditions above the boundary layer, a feature inherent to the BFZ, and played an important role in minimizing the reduction in the buoyancy of air parcels. The results of this study indicate that a better forecast of the horizontal distribution of free tropospheric moist air is beneficial for limiting the potential area of genesis of MCS in the BFZ, and a more comprehensive understanding of the vertical variations in moisture transport contributes to an improved forecast skill for MCS in the BFZ. Plain Language Summary: A very long, stagnant atmospheric front that forms over East Asia in early summer is often associated with a mesoscale convective system (a cloud system that occurs in connection with an ensemble of thunderstorms and produces a contiguous precipitation area) that can cause flash floods. The recent increase in the number of heavy rainfall disasters has led to increased interest in the conditions under which such systems develop around the front. In this study, the conditions favorable for the development of such a system with no remarkable upper‐tropospheric low pressure system were investigated using an unprecedented high‐frequency and dense observation network. The system developed when the influxes of two very moist air masses, one near the sea surface and the other well above the sea surface, overlapped vertically. The moist air near the sea surface ensured that the atmosphere was unstable, and the moist air above contributed to the development of the system by suppressing convection weakening. The findings of this study indicate that a more comprehensive understanding of moist air transport may facilitate more accurate forecasting of convective systems. Key Points: Unprecedented high‐frequency atmospheric soundings of a mesoscale convective system were conducted within the Baiu frontal zoneThe system began to rapidly develop when the influxes of nearly saturated near‐surface and free‐tropospheric air overlappedThe areas where systems potentially develop are sensitive to small variations in the humidity distribution in the free troposphere [ABSTRACT FROM AUTHOR]

Nowadays, clean energy production and reconciliation with nature is one of the best solutions known to rectify the global warming issue. Solar energy, as a clean and green one, has recently been drawing scientists' attention to itself more than ever. Applying parabolic trough solar collectors (PTSCs) is one of the state‐of‐the‐art ways to extract energy from the sun. As one of the most interesting research topics, the thermal efficiency enhancement of PTSCs is studied. The current study demonstrates how the thermal efficiency of PTSCs is enhanced through the application of graphene oxide (GO) nanosheets, as an inexpensive nanomaterial with superb thermal conductivity and unique structure, in thermal oil, namely, Behran oil, as heat transfer fluid, within the effective volume fraction range of 0≤φ≤ $0\le \varphi \,\le $ 0.05. The above‐mentioned analysis is based on the theoretical calculations performed through a mathematical model based on the Taylor series approximation. All the calculations are performed with respect to a PTSC unit of a solar–thermal power plant situated in Shiraz, Iran, as the research case study. In addition, the Nan et al. model is used to analytically predict how the increase in the volume fraction of GO nanosheets raises the thermal conductivity and consequently increases the convection heat transfer coefficient of the nanofluid, leading to the thermal efficiency enhancement of PTSCs. The results reveal a maximum thermal efficiency of 71.10% for the volume fraction of φ= $\varphi =$ 0.05. In comparison to the thermal efficiency of the real‐world case‐study mentioned above with pure thermal oil, that is, 67.71%, the thermal efficiency enhancement by about 5.5%, is achieved. Moreover, it is discussed how the thermal efficiency achieved from GO nanosheets surpasses the ones obtained from the application of particle shape nanomaterials, or carbon nanotubes in the same conditions. [ABSTRACT FROM AUTHOR]

Anomalous tropical longwave cloud‐radiative heating of the atmosphere is generated when convective precipitation occurs, which plays an important role in the dynamics of tropical disturbances. Defining the observed cloud‐radiative feedback as the reduction of top‐of‐atmosphere longwave radiative cooling per unit precipitation, the feedback magnitudes are sensitive to the observed precipitation data set used when comparing two versions of Global Precipitation Climatology Project, version 1.3 (GPCPv1.3) and the newer version 3.2 (GPCPv3.2). GPCPv3.2 contains larger magnitudes and variance of daily precipitation, which yields a weaker cloud‐radiative feedback in tropical disturbances at all frequencies and zonal wavenumbers. Weaker cloud‐radiative feedbacks occur in GPCPv3.2 at shorter zonal lengths on intraseasonal timescales, which implies a preferential growth at planetary scales for the Madden‐Julian oscillation. Phase relationships between precipitation, radiative heating, and other thermodynamic variables in eastward‐propagating gravity waves also change with the updated GPCPv3.2. Plain Language Summary: High‐altitude, widespread anvil clouds are generated when heavy convective precipitation occurs in the tropics. These clouds are not only a passive product produced by convection, but they also can subsequently enhance convection by trapping upward infrared radiative flux emitted by the Earth, effectively heating the atmosphere. This additional radiative heating effect can induce upward motion in the tropics, supporting the convective systems by transporting more humid air from below. However, the strength of this cloud‐radiative feedback is hard to estimate because global, continuous observations of surface precipitation are difficult to derive. In this study, the strength of the radiative feedback is calculated using the same product of observed radiative heating against two different observational precipitation products. A newer improved precipitation product yields much weaker radiative feedback strengths for all types of tropical weather systems. In addition, cloud‐radiative heating is found to substantially lag behind precipitation in certain fast, eastward‐propagating tropical rainfall systems in the newer precipitation product, unlike the older one. Why such a lag exists is unclear. The discrepancy of the estimation of cloud‐radiative feedback strengths and properties in the older versus the newer precipitation products indicates that our understanding of mechanisms supporting tropical disturbances is still incomplete. Key Points: The updated Global Precipitation Climatology Project (GPCP) precipitation product has more frequent high rain rates, yielding a weaker longwave radiative feedbackThe updated radiative feedback supports less moistening of the Madden‐Julian oscillation, but imposes stronger planetary scale selectionThe phase relationship between precipitation and thermodynamic fields in eastward‐propagating tropical waves are sensitive to GPCP versions [ABSTRACT FROM AUTHOR]

Observations and models show that near‐surface relative humidity is nearly constant at ∼80% over the ocean in the current climate, and almost invariant in the global mean in projected future climates. Here, this behavior is investigated through the development of a simple theoretical model for near‐surface relative humidity by considering the moisture balance above a uniform ocean surface. The relative humidity is predicted to depend on only the near‐surface wind speed, air‐surface temperature difference, surface wetness and large‐scale moisture convergence. Although developed in the context of moist over‐ocean convection, the theory is able to determine the relative humidity in a suite of idealized simulations over both wet and dry surfaces with a root‐mean‐square error of less than 3%. The theory also predicts the climatology of relative humidity over the ocean with a root‐mean‐square error of less than 3%. The theory thus provides a theoretical basis for investigating changes in relative humidity over the ocean, water vapor feedbacks and the water cycle in current and future climates. Plain Language Summary: Relative humidity is the water content of air relative to its saturation value. Observations and climate models show that global mean near‐surface relative humidity is almost invariant in a changing climate, an observation which underpins the enhancement of the water cycle with increasing global mean temperatures and surface radiative feedbacks. Furthermore, relative humidity over the ocean, whether in the tropics or polar regions, takes a near uniform value of ∼80%. However, a theoretical basis for this remarkable invariance of relative humidity has not been previously established. Here we show that near‐surface relative humidity is controlled by the geometry of moist convection over the ocean surface. Its value is set by a non‐dimensional geometric constant and is independent of the absolute air temperature, with weak dependence on near‐surface wind speeds, air‐surface temperature difference and large‐scale moisture convergence. Hence, the over ocean relative humidity is largely climate and latitude invariant. Key Points: Convection above the ocean surface exhibits a characteristic geometry that controls the value of near‐surface relative humidityA quadratic equation is derived to predict near‐surface relative humidity in terms of known surface properties and a geometric constantThe equation predicts the relative humidity in idealized simulations and ocean observations with less than 3% error [ABSTRACT FROM AUTHOR]

Seeley and Wordsworth (2021, https://doi.org/10.1038/s41586‐021‐03919‐z) showed that in small‐domain cloud‐resolving simulations the temporal pattern of precipitation transforms in extremely hot climates (≥320 K) from quasi‐steady to organized episodic deluges, with outbursts of heavy rain alternating with several dry days. They proposed a mechanism for this transition involving increased water vapor greenhouse effect and solar radiation absorption leading to net lower‐tropospheric radiative heating. This heating inhibits lower‐tropospheric convection and decouples the boundary layer from the upper troposphere during the dry phase, allowing lower‐tropospheric moist static energy to build until it discharges, resulting in a deluge. We perform cloud‐resolving simulations in polar night and show that the same transition occurs, implying that some revision of their mechanism is necessary. We perform further tests to show that episodic deluges can occur even if the lower‐tropospheric radiative heating rate is negative, as long as the magnitude of the upper‐tropospheric radiative cooling is about twice as large. We find that in the episodic deluge regime the period can be predicted from the time for radiation and reevaporation to cool the lower atmosphere. Plain Language Summary: Precipitation plays an important role in Earth's climate and habitability, and also influences important weathering processes such as the carbonate‐silicate cycle. In the distant future, Earth may experience a very hot and wet "hothouse" climate, just like it may have in the Archean. Modeling results show that in a hothouse climate, precipitation transforms into an "episodic deluge" pattern, with outbursts of heavy rain alternating with several dry days. In this study, we find that positive lower‐tropospheric heating is not the necessary cause for episodic deluges. Instead, vertical radiative cooling contrast is critical in triggering the episodic deluges in small‐domain hothouse climates. We also try to understand the underlying mechanism of episodic deluges through CIN and CAPE analyses. Key Points: Episodic deluges can occur during polar nightLower‐tropospheric radiative heating is not necessary for the occurrence of episodic delugesA strong vertical gradient of radiative cooling is a key factor in triggering episodic deluges [ABSTRACT FROM AUTHOR]

The Gulf of Lion, Northwestern Mediterranean Sea, is one of few oceanic regions where deep convection occurs. We investigate the restratification following a convection event using measurements from an ocean glider equipped with turbulence microstructure sensors. This unique combination of instruments provides a high‐resolution description of the mixed layer with regard to turbulence, stratification and chlorophyll. We observe a rapid restratification process that proceeds over a timescale of days to one week. We find that restratification exerts a leading order control on surface mixed layer turbulence variability, as abrupt changes in turbulence dissipation rates are associated with the formation of near‐surface stratification. The near‐surface formation of stratification occurs through both the diurnal variability in surface buoyancy fluxes and through lateral advective processes. We conclude that daily near‐surface processes that influence stratification control mixed layer turbulence levels, and thus the phytoplankton response in the critical transition period to spring bloom. Plain Language Summary: During winter in the Gulf of Lion, Northwestern Mediterranean Sea, a unique alignment of ocean conditions allow strong winds to cool the ocean surface enough to cause mixing of the surface waters to great depths in a process known as deep convection. When this event ceases, the water column tends to restore its original configuration, with light waters above dense waters. We capture the onset of this process, known as restratification, in high‐resolution observational detail together with measurements of ocean turbulence levels, collected with an autonomous ocean vehicle. The onset of restratification after convection takes place on a timescale of days to one week, and strongly influences turbulence variations within the surface waters. We conclude that this restratification has two main contributors, the near‐surface stratification that forms due to the daily variation of surface buoyancy fluxes, and the lateral exchange of denser waters from the surroundings. With sufficient light and nutrients after convection, this near‐surface stratification together with the absence of turbulent mixing allow phytoplankton to grow. Key Points: Autonomous glider‐based turbulence measurements have captured restratification in a deep convection regionThe onset of restratification occurs rapidly, over a timescale of days to one weekNear‐surface restratification is a primary control on mixed layer turbulence and phytoplankton growth [ABSTRACT FROM AUTHOR]

A single‐row cross‐flow heat exchanger with wing‐ shaped tubes is designed in this paper using the constructal design method. The wing‐to‐wing spacing and the wing thickness are free to morph while the chord of the wings remains constant. Wing‐to‐wing spacing optimization or heat transfer density maximization from the wings is the objective function in this design. Two directions of the free‐stream (incoming) flow are considered. The right‐ and left‐flow directions are considered with a constant drop in pressure. All wings are heated at a uniform temperature, and the air is used to cool these wings. The two‐dimensional conservation of mass, conservation of momentum, and the conservation of energy equations are solved by means of the finite volume method for steady and incompressible flow. The ratio of the wing thickness to the chord (dimensionless wing thickness) is changed from 0.2 to 1. For each wing thickness, three Bejan numbers (Be = 10³, 104, and 105) are used in the numerical simulation. The results revealed that in the case of the flow direction to the left, the maximum heat transfer density is higher than that in the case of the flow direction to the right for all wing thicknesses and all Bejan numbers. [ABSTRACT FROM AUTHOR]

In this study, we differentiate wet processes from dry processes in shaping the extratropical thermal stratification during the Last Glacial Maximum. Our findings indicate that even during the dry glacial period the influence of wet processes on thermal stratification cannot be overlooked. The applicability of dry and wet baroclinic adjustment theory strongly depends on the seasonality rather than the glaciation as the warm season is characterized by a weaker meridional temperature gradient and increased precipitation than the cold season. Despite that the baroclinic adjustment theory based on effective static stability can be proficiently applied to all seasons, the classical dry baroclinic adjustment theory may be better suited for use during relatively cold seasons. These findings have important implications for understanding processes governing the extratropical thermal stratification, particularly in the context of cold climate. Plain Language Summary: In this study, we examined how different processes affect the formation of the extratropical thermal stratification during the Last Glacial Maximum. We found that both dry and wet processes play a crucial role, with the wet processes being particularly important during warm seasons. Our results suggest that the importance of wet process is largely dependent on the seasonality instead of glaciation. These findings help to improve our understanding of the extratropical thermal stratification and its governing processes, particularly in the context of cold climates. Key Points: The study differentiates wet process from dry process in shaping extratropical thermal stratification during the Last Glacial MaximumEven during the dry glacial period, wet processes still poses a significant influence on thermal stratificationSeasonality governs dry and wet baroclinic adjustment theory applicability, with the dry theory being more suited for cold seasons [ABSTRACT FROM AUTHOR]

The Greenland Sea is a key region for open ocean convection and ventilation, which exhibit a large variability with periods of strong convection and shutdowns. After a long period of weak winter convection (from the 1970s to the early 1990s), a recovery has been reported, beginning in the 1990s and intensifying in the early 2000s until 2013. Using ISAS, an optimal interpolation product based on Argo observations, we document a recent significant weakening of deep convection between 2014 and 2020, accompanied by a continuous warming of the mixed layer but also a freshening after 2014. These hydrographic changes likely increase the ocean stratification and precondition the shutdown of winter convection. We suggest that these property changes result from a shift of the large scale atmospheric circulation, affecting the source of Atlantic Water to the Nordic seas, causing a freshening of about −0.1 g kg−1 that spreads into the Greenland Sea. Plain Language Summary: The Greenland Sea is a key region for the climate system. There, during winter, the ocean loses heat to the atmosphere in a process called "deep convection," that results in the formation of dense water masses that ventilate and fill the deeper layers of the ocean. The Greenland Sea exhibits a high variability in the intensity of winter deep convection, but the scientific community is still debating on which processes trigger or stop convection. After a recovery period of convection, mainly in the beginning of the 21st century, convection has stopped again after 2014 and at least until 2020. Here, we suggest that this new shutdown is mainly caused by changes in the ocean upper layer temperature and salinity that increase the upper ocean buoyancy, making it more difficult to trigger deep convection during winter. We further propose that the main mechanism driving the ocean properties changes is a shift of the large scale atmospheric circulation, which affects the amount and properties of Atlantic Water transported to the Greenland Sea. Key Points: After a period of intense deep convection since 2002, convection in the Greenland Sea has weakened from 2014 to 2020The upper salinity and temperature in the months prior of convection are driving the deep convection variabilityThe upper salinity changes are resulting from changes in large scale pattern of advection [ABSTRACT FROM AUTHOR]

In a "hothouse" climate, warm temperatures lead to a high tropospheric water vapor concentration. Sufficiently high water vapor levels lead to the closing of the water vapor infrared window, which prevents radiative cooling of the lower troposphere. Because water vapor also weakly absorbs solar radiation, hothouse climates feature radiative heating of the lower troposphere. In recent work, this radiative heating was shown to trigger a shift into a novel "episodic deluge" precipitation regime, where rainfall occurs in short, intense outbursts separated by multi‐day dry spells. Here, we further examine the role of the lower tropospheric radiative heating (LTRH) in the transition into the "episodic deluge" regime. We demonstrate that under high sea‐surface temperature the "episodic deluge" regime could be formed even before the LTRH turns positive. In addition, we examine whether these oscillations operate on larger scales and how these oscillations, which represent "temporal" convective self‐organization, would manifest in the presence of traditional "spatial" self‐ or forced‐aggregation in large‐domain convection‐permitting simulations. We find that the temporal oscillations become much less synchronized throughout a large domain (O $\mathcal{O}$ 1,000 km) because gravity waves cannot propagate fast enough to synchronize convection. We also show that temporal oscillations still dominate the rainfall distribution even when there is tropical convective self‐aggregation or a large‐scale overturning circulation. These results could have important implications for extreme precipitation events under a warming climate. Plain Language Summary: Water vapor is a strong greenhouse gas that closely follows surface temperature. Under very warm ("hothouse") conditions, which are believed to have existed in the Earth's distant past, temperature and water vapor are sufficiently high that the greenhouse effect of water vapor prevents heat from escaping out of the lower part of the atmosphere. This trapped heat makes the lower atmosphere even hotter, causing some unusual weather patterns. For example, it was recently shown to lead to short but intense bursts of rain, followed by several days of dry weather. However, it is unclear whether these patterns occur on larger scales and what their characteristic scale is. In this study, computer simulations were conducted to address these uncertainties and to further elucidate the role of the lower tropospheric radiative heating in the transition into this "episodic deluge" regime. We show that these temporal oscillations dominate the rainfall distribution even in the presence of other atmospheric factors such as tropical convective self‐aggregation or large‐scale overturning circulation. Key Points: We examine the temporal and spatial organization of convection in simulated hothouse conditionsWe demonstrate that lower tropospheric radiative heating is not necessary for the "episodic deluge" precipitation regime"Episodic deluge" precipitation regime occurs in self‐ or forced‐convective aggregated large domain simulations but is less synchronized [ABSTRACT FROM AUTHOR]

Radiative‐convective equilibrium (RCE) is particularly well suited for studying tropical deep‐convection, a regime of clouds that contributes some of the highest uncertainties to the estimates of total cloud feedback. In order to perform a comprehensive calculation and decomposition of cloud feedbacks in cloud‐permitting models, previously primarily done in global climate models, the configuration of a satellite simulator for use with offline data was successfully implemented. The resultant total cloud feedback is slightly positive, primarily driven by the longwave effects of increases in cloud altitude. The high‐cloud altitude feedback is robustly positive and has a central value and uncertainty well‐matched with prior estimates. Reductions in high cloud amount drive a tropical anvil cloud area feedback that is on average negative, consistent with prior estimates. However, a subset of models with finer horizontal grid spacing indicate that a positive tropical anvil cloud area feedback cannot be ruled out. Even though RCE is only applicable to tropical deep‐convective clouds, the RCE total cloud feedback is within the range of prior comprehensive estimates of the global total cloud feedback. This emphasizes that the tropics heavily influence the behavior of global cloud feedbacks and that RCE can be exploited to learn more about how processes related to deep convection control cloud feedbacks. Plain Language Summary: Clouds act to simultaneously cool and warm the environment by blocking sunlight from reaching the surface as well as preventing the Earth from emitting heat away from the surface. When the surface temperature warms, different properties of the clouds change in different ways, causing their warming and cooling effects to change. How strongly the clouds cool or warm the surface in a warming climate is the number one source of uncertainty in estimates of the total change in surface temperature to a forced change. This is primarily due to the difficulty the models that are typically used have in simulating clouds. Here, a special kind of model that more accurately simulates clouds is used to study the impact of cloud changes on the total surface warming. Clouds act to warm the environment primarily due to the upward shift in height clouds undergo in a warmer environment. Key Points: A satellite simulator is successfully modified for use with offline model output of atmospheric profilesThe high‐cloud altitude feedback is positive and is the main contributor to the total cloud feedback in radiative‐convective equilibrium (RCE)Tropical cloud feedbacks are well‐captured by RCE [ABSTRACT FROM AUTHOR]

Multidecadal satellite observations indicate that the Antarctic Ice Sheet (AIS) is losing mass at an accelerating rate, which has the potential to impact many aspects of the climate system. While previous studies demonstrated the importance of AIS freshwater (FW) discharge for regional and global climate processes using climate model experiments, many have applied unrealistic FW forcings. Here, we explore potential Southern Ocean (SO) impacts of realistic AIS mass loss over the 21st century in the Community Earth System Model version 2 by applying observation‐based historical and ice sheet model‐based future AIS FW forcing. The added FW reduces wintertime deep convective area by 72% while retaining 83% more sea ice. Congruent with other studies, we find the increased FW discharge extensively impacts local and remote SO surface and subsurface temperature and stratification. These results demonstrate the necessity of accounting for AIS mass loss in global climate models for projecting future climate. Plain Language Summary: We know from several decades of satellite observations that the Antarctic Ice Sheet is losing mass at an accelerating rate. This accelerated mass loss (solid and liquid FW) is often poorly represented—if at all—in global climate models (GCM) and previous studies indicate that even a simple representation of mass loss can have profound climate impacts. Here, we apply a more realistic (in space and time) representation of Antarctic mass loss to a GCM. We find that the added FW leads to more retention of Antarctic sea ice, a decline in wintertime convection of surface waters to the interior ocean, a cooler surface but warmer interior ocean, and a more strongly stratified upper ocean. As such, we argue that properly accounting for Antarctic mass loss in GCMs is imperative for accurately projecting long‐term future climate change. Key Points: We explore impacts of realistic Antarctic Ice Sheet (AIS) freshwater discharge on the Southern Ocean (SO) using a state‐of‐the‐art climate modelAIS discharge drives drastic changes in SO stratification, winter deep convection, surface and interior temperature, and sea iceOur results suggest that regional AIS discharge can have far‐reaching impacts on the SO that can feedback on the climate system [ABSTRACT FROM AUTHOR]

The diffusional process involving elastic collisions between charge carriers and neutrals has long been the predominant candidate for post‐injection momentum loss in the far wider drift region outside confined DC corona discharges in gases. A supplementary research paradigm is here put forward for the interest of a greater understanding of corona‐assisted unipolar ion flows in atmospheric air. In this respect, the auto‐pulsing mode of glow‐type coronas in air is modelled as a source of momentum whose conservation is substantially preserved across the external transfer region. The tangible prospect of charge‐bearing flows in the form of a filamentary convection, with negligible drifting component, in buffer gas is put forward in relation to spontaneous symmetry‐breaking instability. This setting bears some resemblance to the self‐organised collective behaviour of self‐propelled (active) particles. The value of this scheme gains strength precisely in relation to the strong inhomogeneity of the electric field surrounding electrodes prone to go into corona. On such a basis, it is believed that the drift of corona‐generated ions deserves to be reconsidered in view of the arguments set out in the present modelling. [ABSTRACT FROM AUTHOR]

An outer rainband develops rapidly on land of South China from afternoon to evening of 22 August 2017 when Typhoon Hato is approaching, leading to an early arrival of convective storms prior to typhoon's landfall. The convective cells initiate on the eastern coasts and move to the western inland region where they grow upscale into a fully fledged outer rainband. Convective‐permitting simulations suggest that the new‐born convective cells on the eastern coasts are associated with the increasing convective instability and low‐level lifting by the land‐sea differences of non‐gradient winds. Such differences are established by the horizontal and vertical components of thermal contrasts. In the following stage of convection organization, the convectively induced cold pools in turn strengthen the updrafts at their leading edges, which help to organize the convective cells on rainband as a fast‐moving squall line in the western region. Such storm‐feedback processes of rainband convection and cold pools strongly respond to the changing convective instability and mid‐level dry conditions on land. These regional environmental conditions are closely associated with the large‐scale subsidence in the outer region of typhoon. The results highlight that the new outer rainband can form rapidly on land due to surface heating, and the storm‐feedback processes in response to the changing environmental conditions when a tropical cyclone is approaching land. Plain Language Summary: As a tropical cyclone (TC) is approaching large landmass, its outer circulation may interact with the environmental conditions on land, producing convection growth and new rainband far from the cyclone's center. Previous studies noted that the convective systems on outer rainbands tend to form in coastal areas and be organized into a squall‐line pattern. We carried out numerical experiments on an outer rainband to examine its formation under the changing environmental conditions on land. We found that new convections are triggered at the eastern coast with both favorable instability and lifting conditions that are mainly induced by daytime surface heating. Convective systems are organized by rapidly intensifying cold pools in response to the large convective instability and mid‐level dry conditions in the western inland region. The rainband convection decays when these conditions are weakened. Therefore, the changing environmental conditions on land coupled with the outer circulations of TCs can be one of the key factors for understanding and predicting the first engagement of coastal severe weather preceding the landfalls of TCs. Key Points: A new outer rainband forms on land in response to the daytime surface heating and approaching typhoon circulationHorizontal and vertical thermal contrasts induce low‐level non‐gradient winds that lead to the coastal lifting for convection initiationConvection organization and coupled cold pools strongly respond to the changing convective instability and mid‐level dry conditions on land [ABSTRACT FROM AUTHOR]

Existing models of wellbore stability idealize the borehole wall as either a perfectly permeable or an entirely impermeable surface. The widespread observation that a shale borehole allows solvent molecules to pass through but impedes solutes suggests that the borehole wall should be regarded as a non‐ideal semi‐permeable medium. To address the magnitude and rate of fluid penetration into the formation when a semi‐permeable wellbore is exposed to a non‐isothermal drilling fluid quantitatively, this work develops analytical solutions for a semi‐permeable borehole undergoing convective cooling and far‐field non‐hydrostatic in situ stresses in the framework of fully coupled thermoporoelasticity. Integral transform and load decomposition techniques are employed to facilitate the derivation of analytical solutions. The results show that, in contrast to the permeable or impermeable borehole models, the semi‐permeable model predicts significantly different stress and pore pressure fields. The transient evolution of temperature, pore pressure, and stresses is predominantly governed by two non‐dimensional numbers: the Biot number Bi and a newly identified number πf that characterizes the capability of shale to transport fluid across the solid‐fluid interface. [ABSTRACT FROM AUTHOR]

In semi‐arid environments, rainfall‐driven soil moisture fluctuations exert a strong influence on surface turbulent fluxes. Intraseasonal rainfall variability can therefore impact low‐level atmospheric temperatures and influence regional circulations. Using satellite observations and an atmospheric reanalysis, we investigate whether rainfall variability induced by the Madden–Julian oscillation (MJO) triggers land–atmosphere feedbacks across East Africa. We identify that surface fluxes during the East African wet seasons (March–May and October–December) are sensitive to MJO‐induced precipitation variations across low‐lying regions of South Sudan and highland regions of Uganda and southwest Kenya. For example, during MJO phases 6 to 8, when rainfall is suppressed, surface temperatures and sensible heat fluxes increase, whilst evapotranspiration decreases. Spatial variations in the surface flux response to rainfall variability feed back onto the atmosphere through amplifying MJO‐associated pressure anomalies. During dry MJO events for instance, surface warming across the exit region of the Turkana channel increases the low‐tropospheric along‐channel pressure gradient and intensifies the Turkana jet. We conclude that average surface‐driven temperature fluctuations during a single day are responsible for approximately 12% of MJO‐associated variability of the Turkana jet speed. However, we expect that the accumulation of heat over multiple days to the west of the East African Highlands further amplifies anomalies in the pressure gradient and jet intensity. Modelling experiments are required to quantify the accumulated impact of the surface forcing. Surface‐driven Turkana jet variations influence the East African moisture budget and affect the intensity and inland propagation of coastal convection. Not only is this the first study to investigate the importance of intraseasonal land–atmosphere feedbacks across East Africa, but it is also the first to show that Turkana jet characteristics are partly driven by surface conditions. This work motivates an investigation into whether subseasonal forecast models fully harness the predictability from surface‐induced jet variations. [ABSTRACT FROM AUTHOR]

Mesoscale eddies are the important phenomenon of world oceans that play a prominent role in influencing the near‐surface atmosphere and transport of heat. Ocean and atmosphere responses due to the presence of oceanic mesoscale eddies are not well studied in the Northern Indian Ocean (NIO) region. The present study analysed the ocean and atmospheric response due to the presence of mesoscale eddies using a composite analysis. Generally, it is assumed that the anti‐cyclonic eddies are associated with the positive anomalies of sea surface temperature (SST), and cyclonic eddies are accompanied by negative anomalies. However, for the two marginal seas in the NIO, that is, the Bay of Bengal (BoB) and Arabian Sea (AS), the composite picture of SST anomalies associated with mesoscale eddies showed an abnormal response of SST. This unusual behaviour of cold SST near anti‐cyclonic eddies and warm SST near cyclonic eddies in BoB and AS is analysed with the mean composites of precipitation, outgoing longwave radiation (OLR), and turbulent fluxes. The mean composites over all anti‐cyclonic eddies reveal the presence of enhanced precipitation and convection (low OLR), whereas over cyclonic eddies, suppressed convection and negative precipitation anomalies are evident. The composites of latent heat flux (LHF), precipitation and OLR near surface cold anti‐cyclonic eddies indicate the loss of heat from the ocean to the atmosphere, intense precipitation along with cloudy conditions are responsible for the cooling of the ocean. Along with this, stronger winds are also evident during cloudy conditions could play a role in anomalous cooling of SST observed near anti‐cyclonic through intense surface mixing. Similarly, vice versa is observed near the surface warm cyclonic eddies. The overlying atmosphere and abnormal response of SST near oceanic eddies are essential for understanding the significant role of oceanic mesoscale eddies in influencing the large‐scale circulation of the atmosphere and climate. [ABSTRACT FROM AUTHOR]

The auroral oval morphology has been investigated in previous studies presenting maps of average auroral precipitation. However, such distributions tend to emphasize auroral intensity rather than the actual extent of the auroral oval. We develop a statistical method to characterize the auroral oval morphology by using 20 years of electron energy flux measurements from the Defense Meteorological Satellite Program/Special Sensor J (DMSP/SSJ); instead of relying on auroral oval boundaries, we derive the probability of observing aurora from a threshold of 2.109 eV/cm2/s/sr above which the total energy flux of electrons (in the energy range 1–30 keV) is defined as aurora. We then investigate the auroral occurrence probability (AOP) in the magnetic latitude‐magnetic local time (MLat‐MLT) sectors covered by DMSP for various conditions related to geomagnetic activity. Regardless of those conditions, the AOP distributions reveal a width asymmetry with a wider dawn‐to‐noon sector (06–12 MLT) compared to the dusk‐to‐midnight sector (18–24 MLT), the dawn preference getting even more pronounced as the geomagnetic activity decreases. In the context of an open magnetosphere, we investigate the relation between the observed extent asymmetry in the auroral oval and the magnetospheric plasma convection. Representing the plasma sheet magnetic flux as a one‐dimensional fluid subject to production on the nightside (closing of flux via reconnection) and loss on the dayside (opening of flux), we highlight similarities with the AOP in terms of MLT asymmetries. Finally, making use of this fluid model, we demonstrate that the corotation influence on the plasma convection pattern is consistent with the dawn‐dusk asymmetry observed in the AOP distributions. Plain Language Summary: As an indirect consequence of the magnetic interaction between solar wind and Earth, protons and electrons precipitate into the ionized upper atmosphere (ionosphere) at high latitudes. These charged particles can excite atmospheric atoms at approximately 100–200 km altitude, which in turn potentially emit photons in the visible light spectrum during relaxation; this is what we call aurora. However, instruments aboard satellites crossing the polar regions, where aurora take place, can measure particles that will not necessarily result in sharp, visible aurora from the ground. This diffuse aurora represents the largest part of the total auroral energy deposited into the ionosphere. We show that the probability to measure this type of aurora is close to one within an oval‐shaped region (auroral oval) around each pole, at all local times (including daytime), independently of geomagnetic conditions. We find a systematic pattern in the statistical extent of the diffuse auroral oval depending on local time, with a larger oval in the dawn region, compared to dusk. We aim at understanding the auroral oval morphology in terms of large‐scale magnetospheric plasma dynamics, also including the Earth's rotation influence. Key Points: The auroral occurrence probability (AOP) is derived from Defense Meteorological Satellite Program/Special Sensor J measurements for investigating the auroral oval shape and extentThe distribution of AOP is persistently larger at dawn than at dusk, regardless of external conditionsA simple model of plasma sheet magnetic flux indicates that Earth's rotation may contribute to the observed dawn‐dusk asymmetry [ABSTRACT FROM AUTHOR]

Mesoscale convective systems (MCSs) in the tropics play an integral role in the water cycle, are associated with local hazardous weather conditions, and have significant remote impacts on the midlatitude jet stream. Although it is known that MCSs occur in relatively moist environments, it is unclear how far in advance favorable ingredients (lift, instability, and moisture) in the mesoscale environment precede MCS formation. In this study, an automated MCS tracking algorithm and global reanalyses are used to examine the pre‐MCS environment for 3295 MCSs that occurred in the tropics in a 3‐month period. Results showed that increased water vapor and mesoscale ascent implied by low‐level convergence and upper‐level divergence preceded MCS formation by up to 24 h. Regional variations in pre‐MCS environment conditions were apparent and are discussed. Future work will study to what extent these moisture and wind anomalies can be used to predict MCS formation. [ABSTRACT FROM AUTHOR]

We introduce a minimal stochastic lattice model for the column relative humidity (R) in the tropics, which incorporates convective moistening, horizontal transport and subsidence drying. The probability of convection occurring in a location increases with R, based on Tropical Rainfall Measuring Mission observations, providing a positive feedback that could lead to aggregation. We show that the simple model reproduces many aspects of full‐physics cloud resolving model experiments. Depending on model parameter settings and domain size and resolution choices, it can produce both random and aggregated equilibrium states. Clustering occurs more readily with larger domains and coarser resolutions, in agreement with full‐physics models. Using dimensional arguments and fits from empirical data, we derive a dimensionless parameter which we call the aggregation number, Nag, that predicts whether a specific model and experiment setup will result in an aggregated or random state. The parameter includes the moistening feedback strength, the horizontal moisture transport efficiency, the subsidence timescale, the domain size and spatial resolution. Using large ensembles of experiments, we show that the transition between random and aggregated states occurs at a critical value of Nag. We argue that Nag could help to understand the differences in aggregation states between full‐physics, cloud resolving models, which show little consensus about the robustness of self‐organized patterns, whose emergence appears to be sensitive to the model setup, physics and parameterizations. Plain Language Summary: Dynamical models of convection including detailed representation of microphysics and radiative processes can simulate idealized states of radiative‐convective equilibrium. Sometimes in these simulations the tropical atmosphere shows a behavior whereby all convective storms evolve from a state where they occur randomly in space, to one where they are clustered together, with large areas of the simulation domain free from convection. This phenomenon is important to understand due to its implications for climate sensitivity, but the problem is that these full‐physics models do not agree on when or how clustering occurs. We therefore introduce a much simpler stochastic model of the tropical atmosphere, whose minimal representation of the physics is nevertheless adequate to reproduce much of the behavior of the full‐physics models. Convection can aggregate or remain random, depending on the model parameter settings as well as the domain size and resolution chosen. The simplicity of the model allows us to derive a dimensionless parameter, which we call the aggregation number and incorporates all the model parameters and the domain size and resolution. Convection is found to aggregate when this parameter falls below a critical threshold. We suggest that this parameter can help to explain the differences between the full‐physics models. Key Points: A stochastic reaction‐diffusion model of the tropics can simulate aggregated and random convective statesThe model produces a similar sensitivity to domain size and resolution as full‐physics modelsA dimensionless parameter called the aggregation number combines model and experiment configuration parameters to predict aggregation onset [ABSTRACT FROM AUTHOR]

The vigor of the thermal convection in a terrestrial magma ocean tends to prevent the sedimentation of the solid grains. Understanding of the overall dynamical behavior of this solid phase segregation is required to anticipate the solidification mechanisms in the early Earth mantle. We develop numerical models to monitor the crystal fraction evolution of a convecting magmatic reservoir. Our models show that the ability of the crystal fraction to disperse or sediment within the domain strongly depends on the crystal size, the density difference and the magma viscosity. Our models show that the critical value of the convection/buoyancy stress ratio separating sedimentation/suspension regimes can be smaller than 0.1. Hence, during the early crystallization of a magma ocean, suspension should be the dominant process. We then investigate the possibility of bridgmanite segregation by comparing the density difference between the MO and the solid crystals for different compositions and the critical density contrast above which crystal segregation is likely to occur. We define the relevant set of parameters; including the P‐V‐T equations of state of coexisting melt and bridgmanite in the mushy MO. We observe that bridgmanite grains are unlikely to segregate in a mantle of pyrolite composition. However, bridgmanite segregation is more likely to occur at the bottom of a MO enriched in SiO2, compared to pyrolite. When a solidifying layer contains 60% of bridgmanite and 40% of melt, we observe a significant SiO2 enrichment with increasing mantle depth in a primitive mantle compatible with seismic and geochemical observations. Plain Language Summary: Following the giant impact that formed the Earth‐Moon system, the Earth's mantle probably underwent a major melting episode forming a magma ocean several hundred kilometers thick. During the solidification of this magma ocean, the first crystals either settled at depth or were efficiently mixed with the magma. This process played a determining role in the chemical composition of the early mantle. We have developed numerical models to monitor the evolution of a thin layer of crystals in a magma ocean. Our models characterize the influence of crystal size, magma viscosity and density difference between crystals and magma. Our models support efficient mixing of crystals in the magma ocean. However, in some settings such as a SiO2‐rich magma ocean, bridgmanite grains may separate from the magma and form a solid layer at the base of the Earth's mantle early during cooling. This process may generate SiO2 enrichment with depth in agreement with seismic and geochemical observations. Key Points: We develop numerical models to monitor the crystal fraction evolution within a convecting magma oceanWe illustrate that during the early crystallization of a magma ocean, suspension should be the dominant process compared to sedimentationWe observe that bridgmanite segregation is more likely to occur at the bottom of a MO enriched in SiO2 compared to pyrolite [ABSTRACT FROM AUTHOR]

Ice crystal icing (ICI) poses a threat nowadays for airplane pilots crossing the anvils of tropical mesoscale convective systems (MCSs). The use of fine‐scale operational numerical weather predictions as provided by the French limited‐area model AROME could help to better understand this phenomenon and to help its anticipation. To enable AROME to simulate ICI‐prone conditions, modifications of its single‐moment microphysical scheme Intercity‐Express 3 (ICE3) are tested. Using a temperature‐dependent snow particle distribution deeply impacts the organization and the ice phase of the simulated MCS. Notably, while the size of convective regions decreases, the size of anvil clouds increases and the low stratiform rain increases as well. As a result, by increasing the quantity of snow and decreasing the quantity of graupel, the simulation of ICI‐prone conditions in the anvils of convective systems is enabled. Using this parametrization, further modifications fine‐tune the representation of snow and further increase the size of the anvil cloud. The Marshall–Palmer snow distribution is replaced by a generalized gamma and the terminal fall velocities of snow hydrometeors are parametrized so that they are in closer agreement with observations. [ABSTRACT FROM AUTHOR]

The precipitation anomaly over Borneo features a dipolar pattern under the influence of the Madden‐Julian Oscillation (MJO). To understand the formation mechanisms of this pattern, a linear theory is developed to study the factors controlling its diurnal cycles and the dipolar pattern. The theory predicts that the prevailing wind is primarily responsible for the asymmetry over an idealized island, while the topography plays a critical role in the leeward convergence and convection asymmetry. The results are largely consistent with the observed composites of the dipole at Borneo. Nonlinear cloud‐permitting simulations are further conducted to test the effects of island topography and solar radiative heating in different MJO phases. The results show that the island topography can cause the mesoscale flow to split around the mountain due to the topographic blocking, and favor the development of the lee side sea breeze. These processes strengthen the low‐level convergence and convection at the leeside of the island during the late afternoon and night, which is very important to the formation of island dipolar precipitation anomaly. In contrast, the inland convergence is weakened and the dipole disappears when the terrain is flattened. The diurnal cycle of solar insolation is the dominant factor driving the land‐sea breeze circulation, which intensifies the island convection at the leeside. These results indicate that the MJO wind anomaly, island topography and solar insolation play distinct roles in the formation of the dipolar pattern of Borneo precipitation. Plain Language Summary: Rainfall over the Borneo island varies significantly during the course of a day. It initiates during the late afternoon, reaches the peak during the late night, and propagates offshore afterward. Rainfall is often enhanced in western Borneo, and suppressed in its east region every 20–90 days. This spatial pattern also reverses sometimes. While these characteristics are important for predicting of rainfall over the tropical island, it remains unclear where the pattern comes from. Here, we study the factors that controls these characteristics. We consider three important factors: solar insolation that varies during time of the day, low‐level zonal wind that changes every 20–90 days, and the island topography. Results from a simple model and complex numerical simulations indicate that all these factors make distinct contributions to the rainfall pattern over the island. Key Points: A linear theory suggests that the dipolar pattern of precipitation over Borneo is primarily caused by intraseasonal wind associated with the Madden‐Julian Oscillation (MJO)Cloud‐permitting numerical simulations indicate that the island topography can strengthen the dipole in the presence of the prevailing windSolar insolation, MJO intraseasonal zonal wind, and island topography are all important for the precipitation dipole over Borneo [ABSTRACT FROM AUTHOR]

The meteorological characteristics of cloudy atmospheric columns can be very different from their clear counterparts. Thus, when a forecast ensemble is uncertain about the presence/absence of clouds at a specific atmospheric column (i.e., some members are clear while others are cloudy), that column's ensemble statistics will contain a mixture of clear and cloudy statistics. Such mixtures are inconsistent with the ensemble data assimilation algorithms currently used in numerical weather prediction. Hence, ensemble data assimilation algorithms that can handle such mixtures can potentially outperform currently used algorithms. In this study, we demonstrate the potential benefits of addressing such mixtures through a bi‐Gaussian extension of the ensemble Kalman filter (BGEnKF). The BGEnKF is compared against the commonly used ensemble Kalman filter (EnKF) using perfect model observing system simulated experiments (OSSEs) with a realistic weather model (the Weather Research and Forecast model). Synthetic all‐sky infrared radiance observations are assimilated in this study. In these OSSEs, the BGEnKF outperforms the EnKF in terms of the horizontal wind components, temperature, specific humidity, and simulated upper tropospheric water vapor channel infrared brightness temperatures. This study is one of the first to demonstrate the potential of a Gaussian mixture model EnKF with a realistic weather model. Our results thus motivate future research toward improving numerical Earth system predictions though explicitly handling mixture statistics. Plain Language Summary: The accuracy of a computer weather forecast often depends on the accuracy of the information inputted into the computer forecast system. The accuracy of the input in turn depends on the accuracy of the input‐constructing algorithm. Such algorithms often use probabilistic forecasts from an earlier point in time and current atmospheric measurements to construct the inputs. A common assumption in such algorithms is that the probabilistic forecasts follow a multivariate normal distribution (henceforth called the normality assumption). However, in the frequent situation where the probabilistic forecast is uncertain about the presence/absence of clouds, the normality assumption is violated. This is because clear atmospheric columns and cloudy atmospheric columns have distinctly different thermodynamic and dynamic characteristics. These two types of columns thus have different statistics. As such, when a probabilistic forecast is uncertain about the presence/absence of clouds, it has mixed statistics (henceforth termed mixed probabilistic forecast). Addressing such mixtures can potentially improve forecasts. In this study, we propose a new input‐constructing algorithm that can explicitly handle mixed probabilistic forecasts. This new algorithm is nearly as fast as currently available algorithms. More importantly, our experiments demonstrate that our new algorithm can produce more accurate forecast inputs than an existing popular algorithm. Our work thus suggests that weather forecasts can be improved by upgrading input‐constructing algorithms to treat a common situation where the normality assumption is violated. Key Points: Current ensemble data assimilation (DA) methods assume that forecasts follow a normal distribution. This assumption is often invalidIn this study, we propose a computationally efficient ensemble DA method that handles clear and cloudy forecasts separatelyThis study uses a realistic weather model (WRF) to show that this method can outperform the EnKF [ABSTRACT FROM AUTHOR]

On the evening of November 12, 2019, an exceptional high tide – the second‐highest in the ranking since sea‐level data have been recorded – hit the city of Venice in northern Italy and its entire lagoon, damaging a large part of its historical center. A small warm‐core mesoscale cyclone, which formed in the central Adriatic Sea and intensified during its northwestward movement toward the Venice lagoon, was responsible for the event. The cyclone was preceded by intense northeasterlies (Bora) in the northern Adriatic, which turned to southeasterlies (Sirocco) and then southwesterlies after its passage. Simulations with different initialization times were carried out with the Weather Research and Forecasting (WRF) model. Simulation results show a strong sensitivity to the initial conditions, since the track (and strength) of the cyclone was determined by the exact position of an upper‐level potential vorticity (PV) streamer. The factors responsible for the cyclone development and its characteristics are also investigated. The pre‐existence of positive low‐level cyclonic vorticity, associated with the convergence of the Sirocco and Bora winds in the central Adriatic, made the environment favorable for cyclone development. Also, the interaction between the upper‐level PV anomaly and the low‐level baroclinicity, created by the advection of warm, humid air associated with the Sirocco, was responsible for the cyclone's intensification, in a manner similar to a transitory (stable) baroclinic interaction at small horizontal scales. Sensitivity experiments reveal that convection, latent heat release and sea‐surface fluxes did not play a significant role, indicating that this cyclone did not show tropical‐like characteristics, notwithstanding its low‐level warm core. Thus, the warm‐core feature appears mainly as a characteristic of the environment in which the cyclone developed rather than a consequence of diabatic processes. Lastly, the cyclone does not fall into any of the existing categories for Adriatic cyclones. [ABSTRACT FROM AUTHOR]

Spring extreme precipitation (SEP) significantly disturbs spring ploughing over Southwest China (SWC), bringing challenges for agricultural activities and production over the region. This study investigates the interannual relationship between SWC SEP and sea surface temperature (SST) in preceding winter, from a perspective of prediction. It is found that the dominate mode of SWC SEP interannual variability mainly reflects the variability over the eastern part. The variability of eastern SWC SEP has an enhanced connection with a dipole SST pattern over the South Indian Ocean in preceding winter after the late 1980s. Under the warmer SST background after the late 1980s, the South Indian Ocean dipole SST pattern can lead to significant convection activity over tropical central and western Indian Ocean. The tropical diabatic heating associated with enhanced convection can strengthen the western North Pacific anticyclone, which transports more water vapour to eastern SWC and induces stronger moisture convergence there, providing favourable moisture condition for the SEP occurrence. In addition, the dipole SST pattern can strengthen upward motion over eastern SWC through exiting a meridional circulation, providing a favourable dynamic condition for the SEP occurrence over there. In contrast, under the colder SST background before the late 1980s, the dipole SST pattern‐related convection and atmospheric circulation anomalies are weak over the Indo‐Pacific region. Therefore, the relationship of the dipole SST pattern with SEP over eastern SWC is weak before the late 1980s. The SST signals with one‐season leading could provide valuable source for seasonal prediction of eastern SWC SEP variability after the late 1980s. [ABSTRACT FROM AUTHOR]

This study investigates the spontaneous self‐aggregation of convection in non‐rotating Radiative‐Convective Equilibrium (RCE) simulations performed by the CNRM‐CM6‐1 General Circulation Model within the framework of the RCE Model Intercomparison Project (RCEMIP). In this model, the level of convection self‐aggregation at equilibrium, as quantified by metrics based on moisture or moist static energy, strongly increases with sea surface temperature (SST). As it gets warmer, the troposphere gets drier, high cloud cover diminishes in dry regions, the top of high cloud rises and their thickness increases in moist regions, and low‐cloud cover increases. At high SSTs, the large‐scale circulation exhibits a shallow component, stronger than its deep counterpart. The transition toward self‐aggregation has a similar first 20‐day phase for all SSTs within the 295–305 K range. It primarily involves radiative positive feedback processes. Then, for SSTs above approximately 298 K, a new, slower, transition toward higher levels of self‐aggregation occurs. It is concomitant with a shift from a top‐heavy to a more bottom‐heavy large‐scale circulation, a strengthening of the shallow circulation and a reduced mobility of convective aggregates. This second transition is mostly driven by the dry regions, still involves longwave radiative positive feedbacks, but also advective positive feedbacks in the driest regions. It is argued that boundary‐layer radiative cooling difference between moist and dry regions, which is stronger at high SSTs, is instrumental in this second phase of self‐aggregation. The sensitivity of deep convection to environmental dry air also likely acts as a positive feedback on the system. Plain Language Summary: In idealized configurations of the Earth, convective clouds can spontaneously organize into large clusters: this is convective self‐aggregation. We investigate the sensitivity of this process to surface temperature in the atmospheric component of the state‐of‐the‐art global climate model CNRM‐CM6‐1. For surface temperatures spanning a typical range of tropical conditions (295–305 K), the model exhibits an aggregated state when equilibrium is reached. As the surface gets warmer, convection is more aggregated, the troposphere gets drier, high clouds get less frequent in dry regions and low‐cloud cover increases. When starting from homogeneous conditions, an initial rapid phase of self‐aggregation occurs in all experimented sea surface temperatures. Radiative processes are instrumental in leading to self‐aggregation. For warm surface temperature above approximately 298 K, a second, slower, transition occurs and leads to higher levels of self‐aggregation. It is associated with an adjustment of the large‐scale circulation, in which shallow circulations in the lower troposphere (surface‐700 hPa) and between dry and moist regions strengthen. The radiative loss of energy within the boundary layer, and its unbalanced state between dry and moist regions after the initial transition is argued to be the main process at play. Key Points: The sensitivity to surface temperature of convective self‐aggregation under radiative‐convective equilibrium is documented in CNRM‐CM6‐1Increase of self‐aggregation with surface temperature is associated to an efficient shallow circulation between dry and moist regionsA second slower transition toward self‐aggregation at high surface temperature is primarily driven by radiative processes in dry regions [ABSTRACT FROM AUTHOR]

We examine the heat and mass transfer on magnetohydrodynamic Casson fluid motion via a curved sheet. The fluid flow is assumed to be along a stretched curved sheet. The effects of Soret ("viscous dissipation") and Dufour ("cross dispersion") are taken into account. The governing partial differential equations have been transformed into ordinary differential equations by using relevant similarity transformations. These converted equations are solved using a combination of Runge–Kutta–Fehlberg along with the shooting technique algorithm. We find out the various physical parameter behavior of F′(η) $F^{\prime} (\eta)$, Θ(η) $\Theta (\eta)$, and Φ(η) $\Phi (\eta)$. We found that the Θ(η) $\Theta (\eta)$ ("temperature profile") enhances while opposite behavior of Φ(η) $\Phi (\eta)$ ("concentration profile") with enlarge values of Sr $Sr$ and Df $Df$. Also, we get a good agreement with the present results when compared with the previous study. [ABSTRACT FROM AUTHOR]

The Irminger Sea is one of the few regions in the ocean where deep (>1,000 m) convection occurs. Convection is followed by restratification during summer, when the stratification of the water column is reestablished and the convectively formed water is exported at depth. There are currently no descriptions of interannual variability and physical drivers of restratification in the Irminger Sea. We investigate restratification in the upper 600 m of the central Irminger Sea using reanalysis data for the years 1993–2019. We find distinctly different restratification processes in the upper 100 m (the upper layer) and the water below it (the lower layer). In the upper layer, the stratification is dominated by a seasonal cycle that matches the cycle of the surface heat flux. In 2010 and 2019, there were peaks in upper layer restratification, which could partly be related to strong atmospheric heat and freshwater fluxes. Greenland runoff likely also contributed to the high restratification, although this contribution could not be quantified in the present study. In the lower layer there is strong interannual variability in stratification, caused by variability both in the convection and the restratification strength. The restratification strength is strongly correlated with the eddy kinetic energy in the eastern Irminger Sea, suggesting that lower layer restratification is driven by lateral advection of warm, saline waters through Irminger Current eddies. In the future, surface warming and freshening of the Irminger Sea due to anthropogenic climate change are expected to increase upper layer stratification, potentially inhibiting convection. Plain Language Summary: In the Irminger Sea, cold winters can cause the ocean's surface waters to cool enough that they start mixing downward. The mixing can continue for months and eventually form a dense water mass of more than 1 km deep. This process is called deep convection. During summer, the dense water gets exported at depth, and the water column will go back to its original structure with lighter waters over denser waters. This is called restratification. The formation and export of dense waters in the Irminger Sea plays an important role in the global ocean circulation. Here we study what drives the restratification in the Irminger Sea, and how it varies in time. We find that in the upper 100 m the restratification is influenced by heating from the atmosphere, which warms the surface waters and makes them lighter. Additionally, rainfall or ice melt which make the surface waters fresher can contribute to restratification. Below the surface layer, restratification happens through transport of warm and saline waters from the eastern Irminger Sea. With rising ocean temperatures due to climate change, the Irminger Sea might see more restratification in the future, which might slow down global oceanic heat transport. Key Points: Restratification in the Irminger Sea is distinctly different in the upper 100 m of the water column than belowIn the upper layer, summers with exceptionally high stratification had strong atmospheric heat and freshwater gainIn the lower layer, restratification is driven by lateral advection of warm and saline waters through Irminger Current eddies [ABSTRACT FROM AUTHOR]

We describe and validate a method of calculating convective cloud top altitudes and potential temperatures up to 50° latitude at high spatial (0.25°) and temporal (3 hr) resolution. The approach uses the statistics of the CloudSat cloud radar deep convective cloud classification product coupled with nighttime CALIOP lidar measurements to effectively "calibrate" the high frequency, high resolution global rainfall and brightness temperature data that is used to derive convective cloud top altitudes. Thus, our product agrees well with the statistics of the CloudSat/CALIOP convective cloud tops, especially in the tropics and over oceanic regions. Agreement is reasonable, but not as good, for land‐based convection. The estimated uncertainty in cloud top altitudes in our product is 0.5–1.0 km over land areas, with smaller uncertainties over the oceans. The diurnal cycle of the new convection data set is in good agreement with precipitation radar convective climatology. Plain Language Summary: Convection modifies the water vapor concentration and injects trace gases into the upper troposphere and the lower stratosphere. To quantify the impact of convection, we have developed a data set of convective cloud top altitudes. Our algorithm uses lidar and cloud radar data to calibrate a combination of rainfall and geostationary satellite brightness temperature data to produce a database of convective cloud top altitudes. The statistics of our high‐resolution convective cloud top altitudes agree well with the statistics of other more limited convective cloud top data sets, especially over the oceans and in the tropics. Key Points: A high resolution data set of convective cloud top altitudes is calculated based on rainfall and brightness temperature observationsThe frequency statistics and diurnal cycle of this data set show good agreement with other observationsThe uncertainty in the data set of convective cloud tops is 0.5–1.0 km, or 5–15 K potential temperature [ABSTRACT FROM AUTHOR]

Gravity waves can influence weather and climate patterns on various temporal and spatial scales in the atmosphere. Despite their recognized importance, there are clearly a lack of sufficient and accurate observations from currently available satellite observing systems to satisfy the requirements of many satellite users. Common method to detect gravity waves is to measure brightness temperature (BT) anomalies, which rely on an initial efficient background removal method. Before gravity waves can be extracted from Atmospheric Infrared Sounder raw radiances, Hoffmann and Alexander (2010, http://doi.org/10.1029/2010jd014401) used a fourth‐order polynomial fitting (4PF) method to remove the background variations. In this study, we propose a new strategy, an optimal orthogonal polynomial fitting (OPF) method using Chebyshev Polynomials as basis functions, to remove the background variations and estimate BT perturbations. By extending the classic 4PF method to the fifth‐order polynomial fitting (5PF) method and combining the Cressman interpolation method, some experiments are designed to validate the feasibility and superiority of the OPF method. The results show that OPF is the optimal method to remove the limb‐brightening effect in the extraction of gravity wave signals generated by typhoons. In addition, what we noticed is that an appropriate fitting orders have to be selected to get more accurate BT anomalies signals in the experiments to extract gravity wave signals. Plain Language Summary: Gravity waves can influence weather and climate patterns on various temporal and spatial scales in atmosphere. Despite their recognized importance, there are clearly a lack of sufficient and accurate observations from currently available satellite observing systems to satisfy the requirements of many satellite users. A more accurate gravity wave signal extraction method could provide more accurate gravity wave data for disaster weather and climate studies. Key Points: An Orthogonal Polynomial Fitting (OPF) method using Chebyshev basis functions is proposed to extract gravity wave signals generated by a typhoon (SuLi 1307) deep convectionThe OPF method is an optimal method to remove the background brightness temperature and extract gravity signals from Atmospheric Infrared Sounder dataAlthough the fifth‐order polynomial fitting (5PF) method is inferior to the OPF method, the 5PF method is superior to the fourth‐order polynomial fitting (4PF) method and the Cressman interpolation method [ABSTRACT FROM AUTHOR]

Turbulent convection in a planet's outer core is simulated here using a thermally‐driven, free surface paraboloidal laboratory annulus. We show that the rapidly rotating convection dynamics in free‐surface paraboloidal annuli are similar those in planetary spherical shell geometries. Three experimental cases are carried out, respectively, at 35 revolutions per minute (rpm), 50 and 60 rpm. Thermal Rossby waves are detected in full disk thermographic images of the fluid's free surface. Ultrasonic flow velocity measurements reveal the presence of multiple azimuthal (zonal) jets, with successively more jets forming in higher rotation rate cases. The jets' cylindrical radial extent is well approximated by the Rhines scale. Over time, the zonal jets migrate to larger radial position with migration rates in good agreement with prior theoretical estimates. Our results suggest that planetary core rotating convection will be comprised of flow structures found in other turbulent geophysical fluid dynamical systems: convective turbulence dominates the small‐scale flow field, and also act to flux energy into larger‐scale, slowly evolving zonal flow structures. How the ambient magnetic fields in planetary core settings affect such turbulent flows remains an open question. Plain Language Summary: In this study, proof‐of‐concept demonstrations are provided which show that it is possible to simulate the turbulent fluid motions occurring in Earth's remote outer core via laboratory experiments using a novel device called the Coreaboloid. We show that the Coreaboloid's parabolic free surface configuration is a good proxy for rapidly rotating dynamics in a spherical shell. In our experiments strong zonal jet flows—dynamically similar to those observed on the surfaces of the Gas Giants—emerge naturally from the convective Coreaboloidal turbulence. Further, these jets do not always stay put; in our most rapidly rotating case they slowly travel outwards in radius, an effect seen in studies of atmospheric and oceanic jet dynamics, but that has not be seen in prior experimental studies of planetary core flows. Key Points: Planetary core turbulence is simulated via a rapidly rotating annular device with a parabolic free upper fluid surfaceThermal Rossby waves are found in free surface thermography data; alternating zonal jets are detected in ultrasonic velocimetry dataThe Rhines scale jets travel in radius, in agreement with radial migration rates found in models of two‐dimensional barotropic turbulence [ABSTRACT FROM AUTHOR]