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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]

This paper describes a novel technique that allows separation and quantification of different sources of convection in the high‐latitude ionosphere. To represent the ionospheric convection electric field, we use the Spherical Elementary Convection Systems representation. We demonstrate how this technique can separate and quantify the contributions from different magnetospheric source regions to the overall ionospheric convection pattern. The technique is in particular useful for distinguishing the contributions of high‐latitude reconnection associated with lobe cells from the low‐latitude reconnection associated with Dungey two‐cell circulation. The results from the current paper are utilized in a companion paper (Reistad et al., 2019, https://doi.org/10.1029/2019JA026641) to quantify how the dipole tilt angle influences lobe convection cells. We also describe a relation bridging other representations of the ionospheric convection electric field or potential to the Spherical Elementary Convection Systems description, enabling a similar separation of convection sources from existing models. Key Points: Spherical Elementary Convection Systems (SECS) are used to represent the high‐latitude convection electric fieldA novel technique is presented that allows separation and quantification of different sources of ionospheric convectionThe convection pattern can be separated to quantify the magnetic flux transport associated with different reconnection sites [ABSTRACT FROM AUTHOR]

The purpose of the present paper is testing an in‐house efficiency algorithm based on lattice Boltzmann method (LBM) and using it to resolve the obtained coupled nondimensional governing equations to analyze two‐dimensional free convection inside a cold outer cavity subjected to a heated cylindrical diamond array. Steady state or oscillatory results are obtained using the Bhatnagar‐Gross‐Krook collision model associated to the thermal LBM. Both the velocity and temperature fields are solved using the D2Q9 models. With different Rayleigh numbers (Ra), the tested free convection can either achieve to steady state or oscillatory. We extended our in house Fortran 90 code using curved boundary conditions and implemented them into a cavity with a diamond array. The numerical simulations were done using distinct Ra (106 and 10 7) and distances 0.3≤ε≤0.7 between the four neighboring circular cylinders aligned in a diamond array. The effects of several physical parameters, including Ra and position of the hot body array on flow and heat transfer characteristics are investigated. The obtained results are highlighted in the form of streamlines, isotherms, and velocities plots. We show in this paper the stability and the efficiency of the LBM to deal with a complex geometry and its ability to reach suitable convergence criteria for high Ra (10 6 and 10 7). The numerical results indicate that LBM can simulate numerical problems with a high Ra reaching a steady state where we can depict the change of the flow pattern and enhancement of the heat transfer in the presence of heated diamond array. [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]

Traditional parameterizations of convection are a large source of error in weather and climate prediction models, and the assumptions behind them become worse as resolution increases. Multifluid modeling is a promising new method of representing subgrid‐scale and near‐grid‐scale convection allowing for net mass transport by convection and nonequilibrium dynamics. The air is partitioned into two or more fluids, which may represent, for example, updrafts and the nonupdraft environment. Each fluid has its own velocity, temperature, and constituents with separate equations of motion. This paper presents two‐fluid Boussinesq equations for representing subgrid‐scale dry convection with sinking and w = 0 air in Fluid 0 and rising air in Fluid 1. Two vertical slice test cases are developed to tune parameters and to evaluate the two‐fluid equations: a buoyant rising bubble and radiative convective equilibrium. These are first simulated at high resolution with a single‐fluid model and conditionally averaged based on the sign of the vertical velocity. The test cases are next simulated with the two‐fluid model in one column. A model for entrainment and detrainment based on divergence leads to excellent representation of the convective area fraction. Previous multifluid modeling of convection has used the same pressure for both fluids. This is shown to be a bad approximation, and a model for the pressure difference between the fluids based on divergence is presented. Plain Language Summary: Clouds and buoyant convection are often smaller than the grid size in weather and climate prediction models, but they are of central importance. Therefore, their effects are parameterized—their interactions with the larger scales are estimated based on properties of the larger scales. Convection parameterizations are a large source of error in models of the atmosphere despite decades of effort to improve them. Some unrealistic assumptions remain such as that convection does not provide a net upward transport of mass, convection is in equilibrium with the surroundings, and that the variations in the horizontal direction are not relevant. These assumptions make it much simpler to incorporate convection parameterizations into existing models. Multifluid modeling does not rely on these assumptions, but the approach means a whole new atmospheric model rather than a stand‐alone routine that can be incorporated into an existing model. This paper provides some closures necessary for multifluid modeling and evaluation of the technique for two‐dimensional dry convection. Key Points: Multifluid modeling enables net mass transport by subgrid‐scale convection and nonequlibrium dynamicsMultifluid modeling means a new dynamical core rather than a parameterization for an existing coreClosures for the pressure difference between fluids and entrainment and detrainment are provided [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 paper investigates the link between the Labrador Sea Water (LSW) formation rate and the strength of the Atlantic Meridional Overturning Circulation within the Labrador Sea. LSW is formed in the Labrador Sea through deep wintertime ocean convection and is then carried out of the basin by, among other currents, the Deep Western Boundary Current (DWBC) that flows southward along the east coast of Canada. We used an eddy‐permitting simulation (at 1/12°, horizontal resolution) with an Arctic and Northern Hemisphere Atlantic configuration of the Nucleus for European Modeling of the Ocean (NEMO) model that covers the period from 2002 to 2017. In this study, the formation rate of LSW is estimated using an instantaneous kinematic subduction approach by analyzing the vertical transport of a water mass through the base of the mixed layer. We computed the local Meridional Overturning Circulation (MOC) index and the transport of LSW within the DWBC at the Atlantic Repeat hydrographic section 7 West (AR7W). Results show that an increase in the formation rate of LSW entails an increase in the LSW transport in the DWBC within 1 year. This is followed by an enhancement of the overturning in the Labrador Sea. Plain Language Summary: The Atlantic Meridional Overturning Circulation (AMOC) is of paramount importance for the climate. The AMOC contributes to the redistribution of heat, salt, and anthropogenic carbon in the world's oceans. The upper limb of the AMOC transports warm, surface water northward. The lower limb of the AMOC is associated with dense, cold, and deep water formation and is carried by a vigorous Deep Western Boundary Current (DWBC). The Labrador Sea Water (LSW) is one of the water masses formed by deep convection in the subpolar gyre and then carried out of the basin by, among other currents, the DWBC that flows southward along the east coast of Canada. In this paper, we use a simulation to investigate how the change in the formation rate of the LSW could impact the strength of the local AMOC in the Labrador Sea. We found that an increase in the formation rate of LSW entails an increase in the LSW transport in the DWBC within 1 year. This is followed by an enhancement of the overturning in the Labrador Sea. Key Points: Strong convection events in the Labrador Sea entail a high formation rate of Labrador Sea WaterPart of the Labrador Sea Water is exported out of its formation region through the Deep Western Boundary Current within 1 yearStrong, deep convection events are related to a higher local MOC index in the Labrador Sea along the AR7W section [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]

This paper describes an updated method for automated detection of overshooting cloud tops (OT) using a combination of spatial infrared (IR) brightness temperature patterns and modeled tropopause temperature. IR temperatures are normalized to the tropopause, which serves as a stable reference that modulates how cold a convective cloud should become within a given region. Anvil clouds are identified using histogram analysis and cold spots embedded within anvils serve as OT candidate regions. OT candidates are then assigned an OT probability, which can be interpreted as a metric of storm intensity and an estimate of confidence in a detection for a particular pixel. It is produced using an original mathematical composition of four factors: Tropopause‐normalized temperature, prominence relative to the surrounding anvil, surrounding anvil area, and spatial uniformity of anvil temperature, which are calculated from empirically derived sensitivity curves. The shape of the curves is supported by independent analysis of a large sample of matched IR and radar‐derived OT regions. An optimal sensitivity for each factor was determined by maximizing correlation between the OT probability and a set of human‐identified OT regions. Coarser spatial resolution of GOES‐13 data cause OTs to be less prominent compared to GOES‐16, necessitating different sensitivities for each satellite. Detection performance is quantified for each satellite based on human OT identifications and as a function of how prominent the OT appeared in visible and IR imagery. Based on analyses of human‐identified OTs, OT detection accuracy, defined by the area under a receiver operating characteristic curve, is determined to be 0.94 for GOES‐16 and 0.78 for GOES‐13. Key Points: A new OT detection method combines tropopause‐relative infrared (IR) temperature, anvil‐relative prominence, anvil area and its spatial uniformityOvershooting cloud tops (OT) probability derived from spatial cloud analyses is validated with human‐identified OTs, revealing improvements over previous methodsDiffering imagery spatial resolution necessitates optimization of sensitivity curves to account for warmer observed OTs from coarser imagery [ABSTRACT FROM AUTHOR]

In this paper, we resolve the ever‐present confusion over the Quadratic Upwind Interpolation for Convective Kinematics (QUICK) scheme: it is a second‐order scheme or a third‐order scheme. The QUICK scheme, as proposed in the original reference (B. P. Leonard, Comput. Methods. Appl. Mech. Eng., 19, (1979), 59‐98), is a third‐order (not second‐order) finite‐volume scheme for the integral form of a general nonlinear conservation law with point‐valued solutions stored at cell centers as numerical solutions. Third‐order accuracy is proved by a careful and detailed truncation error analysis and demonstrated by a series of thorough numerical tests. The QUICK scheme requires a careful spatial discretization of a time derivative to preserve third‐order accuracy for unsteady problems. Two techniques are discussed, including the QUICKEST scheme of Leonard. Discussions are given on how the QUICK scheme is mistakenly found to be second‐order accurate. This paper is intended to serve as a reference to clarify any confusion about third‐order accuracy of the QUICK scheme and also as the basis for clarifying economical high‐order unstructured‐grid schemes as we will discuss in a subsequent paper. [ABSTRACT FROM AUTHOR]

Convection is usually parameterized in global climate models, and there are often large discrepancies between results obtained with different convection schemes. Conventional methods of comparing convection schemes using observational cases or directly in three‐dimensional (3D) models do not always clearly identify parameterization strengths and weaknesses. In this paper we evaluate the response of parameterizations to various perturbations rather than their behavior under particular strong forcing. We use the linear response function method proposed by Kuang (2010) to compare 12 physical packages in five atmospheric models using single‐column model (SCM) simulations under idealized radiative‐convective equilibrium conditions. The models are forced with anomalous temperature and moisture tendencies. The temperature and moisture departures from equilibrium are compared with published results from a cloud‐resolving model (CRM). Results show that the procedure is capable of isolating the behavior of a convection scheme from other physics schemes. We identify areas of agreement but also substantial differences between convection schemes, some of which can be related to scheme design. Some aspects of the model linear responses are related to their RCE profiles (the relative humidity profile in particular), while others constitute independent diagnostics. All the SCMs show irregularities or discontinuities in behavior that are likely related to threshold‐related mechanisms used in the convection schemes, and which do not appear in the CRM. Our results highlight potential flaws in convection schemes and suggest possible new directions to explore for parameterization evaluation. Plain Language Summary: The transport of heat up and down the atmosphere, called atmospheric convection, is a complex process. To simplify the representation of convection in global climate models (GCMs) scientists use "parameterization," which is essentially mathematical equations of physical processes. However, there are many different ways to formulate these equations, and no agreement on which is better. In this work we aim to understand a few popular ways to parameterize convection. We extract one vertical column from five different GCMs and lightly tickle (perturb) it and then observe its responses. We found that different models respond very differently to the same tickling, and this tells us a lot about the model. Importantly, the specific perturbation that we used can single out the responses of convection‐related equations from equations of other processes. All the models in our study have one thing in common: They are quite jumpy when tickled, especially at the top of the boundary layer where clouds start to form. We suspect the culprits are thresholds placed in the models that sometimes lead to sudden changes in their response. Our work highlights potentially problematic behavior that can give clues on how to make climate models better. Key Points: The linear response function method is applied in single‐column model (SCM) simulations and is able to isolate the behavior of convection schemesLinear responses of the models are related to the mean state relative humidity in both shape and magnitudeAll SCMs show discontinuities in their responses which are likely related to thresholds used in convective parameterization [ABSTRACT FROM AUTHOR]

Sulfur dioxide is a radiatively and chemically important trace gas in the atmosphere of Venus and its abundance at the cloud tops has been observed to vary on interannual to decadal timescales. This variability is thought to come from changes in the strength of convection which transports sulfur dioxide to the cloud tops, although the dynamics behind such convective variability are unknown. Here, we propose a new conceptual model for convective variability that links the radiative effects of water abundance at the cloud‐base to convective strength within the clouds, which in turn affects water transport within the cloud. The model consists of two coupled equations which are identified as a recharge‐discharge oscillator. The solutions of the coupled equations are finite amplitude sustained oscillations in convective strength and cloud‐base water abundance on 3–9 years timescales. The characteristic oscillation timescale is given by the geometric mean of the radiative cooling time and the eddy mixing time near the base of the convective clouds. Plain Language Summary: Water and sulfur dioxide are important trace gases in the atmosphere of Venus. The photolysis of sulfur dioxide in the upper clouds produces sulfuric acid, which forms the thick cloud decks characteristic of the planet's atmosphere. Sulfur dioxide abundances at the cloud top of Venus (about 70 km altitude) have been observed to oscillate on interannual to decadal timescales. In this paper, we use a simplified model of atmospheric dynamics and chemistry to outline the mechanism that causes such oscillations. The water abundance at the base of the clouds (about 47 km altitude), has a strong influence on the cloud‐base heating and cloud level convection. The cloud level convective mixing in turn determines the gradient of water abundance in the cloud layer, and thereby the cloud‐base water abundance. Thus, the convection and water abundance form a coupled system that oscillates on interannual to decadal timescales, which can explain the timescale of variability in the transport of sulfur dioxide to the cloud tops. Key Points: A simple model is developed to explore relationships between convective activity in the cloud layer and cloud‐base water abundanceSustained recharge‐discharge oscillations exist within this model on interannual to decadal timescalesThe interannual to decadal sulfur dioxide variability at the cloud tops could be a result of these oscillations, instead of explosive volcanic injections [ABSTRACT FROM AUTHOR]

This paper describes a convective system, which brought heavy rainfall leading towards a flash flood on November 25, 2009, over Jeddah city and its surrounding regions. Meteosat Second Generation Spinning Enhanced Visible and Infrared Imager (MSG‐SEVIRI) based near‐real‐time MSG‐RGB (red, green, blue) composites and cloud top temperature images are used for the assessment of convection stages during the event. Tropical Rainfall Measuring Mission (TRMM) data is used to quantify the rainfall amount and found reliable as compared with ground observations. Air mass RGB serves as an effective tool for the visual enhancement of cumulonimbus (Cb) clouds as well as differentiating them from other local features. Cloud top temperatures obtained from MSG IR10.8 channel show that the threshold values of cloud top below 220°K can lead to rainfall with the intensity of 10 mm/hr or above over Jeddah region. The results from MSG‐SEVIRI and TRMM satellite data show that satellite data could serve as an effective tool for the near real‐time monitoring of the rainfall event, when analysing convection stages. The study suggests that where ground measurements are minimal, satellite information can be used in as part of a flood warning system to minimise the aftermaths of a flood disaster. [ABSTRACT FROM AUTHOR]

SUMMARY The aim of this paper is to show that the Jacobi-Davidson (JD) method is an accurate and robust method for solving large generalized algebraic eigenvalue problems with a singular second matrix. Such problems are routinely encountered in linear hydrodynamic stability analysis of flows that arise in various areas of continuum mechanics. As we use the Chebyshev collocation as a discretization method, the first matrix in the pencil is nonsymmetric, full rank, and ill-conditioned. Because of the singularity of the second matrix, QZ and Arnoldi-type algorithms may produce spurious eigenvalues. As a systematic remedy of this situation, we use two JD methods, corresponding to real and complex situations, to compute specific parts of the spectrum of the eigenvalue problems. Both methods overcome potentially severe problems associated with spurious unstable eigenvalues and are fairly stable with respect to the order of discretization. The real JD outperforms the shift-and-invert Arnoldi method with respect to the CPU time for large discretizations. Three specific flows are analyzed to advocate our statements, namely a multicomponent convection-diffusion in a porous medium, a thermal convection in a variable gravity field, and the so-called Hadley flow. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Continuous structural parameterization (CSP) is a proposed method for approximating different numerical model parameterizations of the same process as functions of the same grid‐scale variables. This allows systematic comparison of parameterizations with each other and observations or resolved simulations of the same process. Using the example of two convection schemes running in the Met Office Unified Model (UM), we show that a CSP is able to capture concisely the broad behavior of the two schemes, and differences between the parameterizations and resolved convection simulated by a high resolution simulation. When the original convection schemes are replaced with their CSP emulators within the UM, basic features of the original model climate and some features of climate change are reproduced, demonstrating that CSP can capture much of the important behavior of the schemes. Our results open the possibility that future work will estimate uncertainty in model projections of climate change from estimates of uncertainty in simulation of the relevant physical processes. Plain Language Summary: Numerical models are used to provide estimates of future weather and climate change. The models contain "parameterizations," which are algorithms that simulate the effect of processes too small or poorly understood to represent using physical equations. Although they are based as much as possible on physics, parameterizations are a large source of modeling uncertainty because there can be large disagreements on how to best represent a given process. The method and even the variables used by two different parameterizations may differ. It is therefore very difficult to know how different parameterizations cause numerical models to produce different results and whether the parameterizations we have are adequate and span the range of uncertainty concerning our knowledge of the processes they represent. Using the example of small‐scale atmospheric convection linked to rain and thunderstorms, this paper describes a mathematical method for expressing different parameterizations within the same framework. This allows easy but formal mathematical comparison of different parameterizations and gives future work the potential to understand whether our parameterizations perform as they should in conjunction with future observations. Key Points: CSP is a method for expressing GCM parameterizations as functions of the same grid‐scale variablesThe broad behavior and differences between representations of convection are capturedIf parameterizations are replaced with their CSP emulators in a GCM, stable climates are retrieved [ABSTRACT FROM AUTHOR]

Observations of Jupiter's deep atmosphere by the Juno spacecraft have revealed several puzzling facts: The concentration of ammonia is variable down to pressures of tens of bars and is strongly dependent on latitude. While most latitudes exhibit a low abundance, the Equatorial Zone of Jupiter has an abundance of ammonia that is high and nearly uniform with depth. In parallel, the Equatorial Zone is peculiar for its absence of lightning, which is otherwise prevalent most everywhere else on the planet. We show that a model accounting for the presence of small‐scale convection and water storms originating in Jupiter's deep atmosphere accounts for the observations. Where strong thunderstorms are observed on the planet, we estimate that the formation of ammonia‐rich hail ("mushballs") and subsequent downdrafts can deplete efficiency the upper atmosphere of its ammonia and transport it efficiently to the deeper levels. In the Equatorial Zone, the absence of thunderstorms shows that this process is not occurring, implying that small‐scale convection can maintain a near‐homogeneity of this region. A simple model satisfying mass and energy balance accounts for the main features of Juno's microwave radiometer observations and successfully reproduces the inverse correlation seen between ammonia abundance and the lightning rate as function of latitude. We predict that in regions where ammonia is depleted, water should also be depleted to great depths. The fact that condensates are not well mixed by convection until far deeper than their condensation level has consequences for our understanding of Jupiter's deep interior and of giant‐planet atmospheres in general. Plain Language Summary: Measurements by the Juno spacecraft have shown that much more ammonia is present in Jupiter's atmosphere near the equator than at higher latitudes. This was never predicted by theory. In a companion paper, we showed that ammonia can combine with water to form hail‐like particles that we call "mushballs." Here we show that mushball formation in storms can effectively dry out the atmosphere of its ammonia. Our idea is supported by lack of lightning activity at the equator compared to higher latitudes. Because lightning is generated in rainstorms, the lack of lightning at the equator suggests that the thunderstorms forming the mushballs responsible for the depletion of ammonia are not present there. In contrast, in other regions where lightning is present, we predict that not only ammonia but also water are depleted to great depths, more than a hundred kilometers below the cloud tops. The complexity of Jupiter's meteorology means we must expect similar complexity in observing the weather on other giant planets in and beyond our solar system. Key Points: Juno measurements show that ammonia gas in Jupiter has variable abundance to great depth and as a function of latitudeWe show that Jupiter's powerful storms control ammonia abundance by leading to the formation of water‐ammonia hailstones (mushballs) and evaporative downdraftsA simple atmospheric mixing model successfully links measured lightning rate to ammonia abundance and predicts variable water abundance to great depth [ABSTRACT FROM AUTHOR]

We have investigated the predictability of precipitation using a new configuration of the superparameterized Community Atmosphere Model (SP‐CAM). The new configuration, called the multiple‐instance SP‐CAM, or MP‐CAM, uses the average heating and drying rates from 10 independent two‐dimensional cloud‐permitting models (CPMs) in each grid column of the global model, instead of a single CPM. The 10 CPMs start from slightly different initial conditions and simulate alternative realizations of the convective cloud systems. By analyzing the ensemble of possible realizations, we can study the predictability of the cloud systems and identify the weather regimes and physical mechanisms associated with chaotic convection. We explore alternative methods for quantifying the predictability of precipitation. Our results show that unpredictable precipitation occurs when the simulated atmospheric state is close to critical points as defined by Peters and Neelin (2006, https://doi.org/10.1038/nphys314). The predictability of precipitation is also influenced by the convective available potential energy and the degree of mesoscale organization. It is strongly controlled by the large‐scale circulation. A companion paper compares the global atmospheric circulations simulated by SP‐CAM and MP‐CAM. Key Points: Multiple‐instance superparameterization is described, and its small‐scale ensemble is used to explore precipitation predictabilityA measure of spread, called proportional variability, is found to reliably characterize predictabilityUnpredictable precipitation is related to the CAPE magnitude, degree of mesoscale organization, and proximity to atmospheric critical points [ABSTRACT FROM AUTHOR]

The cloud‐permitting model (CPM) of the superparameterized Community Atmosphere Model (SP‐CAM) is a stochastic parameterization. As reported in a companion paper, we have created a variant of SP‐CAM, called MP‐CAM, that uses the averaged feedback of 10 independent two‐dimensional CPMs in each global model column, in place of the single CPM of SP‐CAM. This ensemble‐averaged feedback is interpreted as an approximation to the feedback from a deterministic parameterization. We present evidence that the multiple‐instance superparameterization of MP‐CAM is indeed more deterministic than SP‐CAM. The climates of the SP and MP configurations are compared, giving particular attention to extreme precipitation events and convectively coupled large‐scale tropical weather systems, such as the Madden‐Julian Oscillation. A number of small but significant changes in the mean state climate are uncovered, and the deterministic parameterization slightly degrades the Madden‐Julian Oscillation simulation. Key Points: Multiple‐instance superparameterization is presented as a more deterministic analogue to standard superparameterizationSeveral measures verify the increased level of determinism resulting from the new parameterizationThe parameterization formulation yields a similar model climate with a slightly degraded MJO [ABSTRACT FROM AUTHOR]

Being one of the first generation of space scientists who entered this field right after the space became accessible to in situ observations, I had good luck of addressing some of the basic questions in this field from the early years of my carrier. These are development of global convection in the magnetosphere when the interplanetary magnetic field has the southward polarity, changes in the structure of the magnetotail leading to the onset of substorm expansion phase, and physics of the plasmapause formation. My career culminated with promotion and implementation of the Geotail spacecraft mission. In this article I shall present my personal recollections on these efforts including interactions with colleagues worldwide who shared the common interest. Plain Language Summary: This article is a recollection of my contributions to space physics in early years of the space age. I chose this discipline for my career because I expected that exciting new problems will emerge out of observations made by Sputnik and numerous scientific satellite missions that should follow. The problems I addressed before 1980 included origin of the plasmapause, mechanism of substorms, and acceleration of trapped particles. (1) Plasmapause is a sharp drop in the plasma density that is always seen in the central region of the magnetosphere. I explained this feature by the combined action of the corotation of plasma with the Earth and the convection of plasma that is generated by the solar wind. I found in the process that this convection is generated when IMF (i.e., magnetic field in the solar wind) is directed southward, suggesting that reconnection of field lines (i.e., connection of field lines having different polarities) occurs at the boundary of the magnetosphere. (2) When this reconnection lasts and field lines are piled up in the magnetotail, another reconnection takes place among the piled‐up field lines, and expansion phase of substorm begins. (3) Plasmas in the magnetosphere can move not only by convection but also by field‐aligned motion and by diffusion. They can be energized from keV to higher energies by taking these trajectories in a gaining order. Since the 1980s, I organized the Geotail satellite mission as a joint program of ISAS of Japan with NASA of USA. This satellite, launched in 1992, covered the key regions of the magnetotail with advanced instruments and credited for deepening the space plasma physics from fluid dynamics to kinetics. Key Points: When IMF is southward, reconnection between IMF and geomagnetic field produces global convection in the magnetosphere named DP2Plasmapause is produced by combined action of DP2 convection and the flow accompanying the Earth's rotationWhen IMF turns southward and field lines are transported to the magnetotail, the plasma sheet becomes thinner and ensuing reconnection in the magnetotail drives the substorm expansion phase (DP1) [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]

This paper introduces a synthetic polarimetric radar simulator and retrieval package, POLArimetric Radar Retrieval and Instrument Simulator (POLARRIS), for evaluating cloud‐resolving models (CRMs). POLARRIS is composed of forward (POLARRIS‐f) and inverse (retrieval and diagnostic) components (iPOLARRIS) to generate not only polarimetric radar observables (Zh, Zdr, Kdp, ρhv) but also radar‐consistent geophysical parameters such as hydrometeor identification, vertical velocity, and rainfall rates retrieved from CRM data. To demonstrate its application and uncertainties, POLARRIS is applied to simulations of a mesoscale convective system over the Southern Great Plains on 23 May 2011, using the Weather Research and Forecasting model with both spectral bin microphysics (SBM) and the Goddard single‐moment bulk 4ICE microphysics. Statistical composites reveal a significant dependence of simulated polarimetric observables (Zdr, Kdp) on the assumptions of the particle axis ratio (oblateness) and orientation angle distributions. The simulated polarimetric variables differ considerably between the SBM and 4ICE microphysics in part due to the differences in their ice particle size distributions as revealed by comparisons with aircraft measurements. Regardless of these uncertainties, simulated hydrometeor identification distributions overestimate graupel and hail fractions, especially from the simulation with SBM. To minimize uncertainties in forward model, the particle shape and orientation angle distributions of frozen particles should be predicted in a microphysics scheme in addition to the size distributions and particle densities. Key Points: New polarimetric radar simulator was developed for CRM evaluationThere are uncertainties remained in the assumptions of axis ratio and canting angles of ice particlesHydrometeor identification allows robust evaluation for bulk and bin microphysics [ABSTRACT FROM AUTHOR]

Midlatitude cyclones with characteristics similar to tropical cyclones (also known as Tropical‐Like Cyclones, TLCs, or medicanes) are sometimes observed in the Mediterranean region. The Wind Induced Surface Heat Exchange (WISHE) mechanism has been considered responsible for their development, in analogy with tropical‐cyclone theory. However, some recent papers have proposed a different explanation, suggesting that the deep warm core in the TLC is mainly an effect of the seclusion of warm air in the cyclone core. To investigate the latter hypothesis, two case‐studies of Mediterranean TLCs are analysed here by means of high‐resolution numerical experiments. The evolution of the near‐surface equivalent potential temperature is followed along back‐trajectories around the cyclone centre, showing for both cases a strong heating when the parcel moves from the outer part of the cyclone to its inner, warmer core. Sensitivity experiments clarify the mechanism of cyclone intensification and the way the warm‐core structure is generated, showing that sea‐surface fluxes and/or condensation latent heating are fundamental to explain the intensification of the cyclones. However, the importance of air–sea interaction processes is case dependent. For the first cyclone, the intense sea‐surface fluxes, associated with tramontane and cierzo winds over the western Mediterranean Sea, transfer a large amount of energy from the ocean to the atmosphere in the area where the cyclone developed, so that the vortex is able to sustain itself in a barotropic environment and reach a tropical‐like structure at a later stage in its lifetime. For the second cyclone, the cyclone never develops a fully tropical‐like structure, evolving in the baroclinic environment associated with the potential vorticity streamer in which the cyclone formed. Based on the distinction emerging in this and other articles, a classification of medicanes in three different categories is proposed. [ABSTRACT FROM AUTHOR]

Midlevel Cloud‐base Turbulence (MCT) caused by ice/snow precipitation from midlevel clouds falling into dry air below the cloud base and sublimating is investigated. MCT phenomena in the lower troposphere as revealed by the Middle and Upper atmosphere (MU) radar in Shigaraki, Japan, during the Shigaraki unmanned aerial vehicle and radar Experiment campaigns in the spring‐summer of 2015 and 2016 are described. The MU radar was operated in a high‐resolution (~20‐m) range imaging mode and hence revealed the structure of these MCTs in great detail. These MCT layers grew to hundreds of meters in thickness, often reaching nearly 2,000 m in depth, lasting often for as much as 24 hr. A simple analytical model and a second‐moment closure‐based turbulent mixing model are used to estimate the levels of turbulence kinetic energy and its dissipation rate in the MCT layer and compare them to those measured by the MU radar. The study shows that MCT can give rise to moderate levels of turbulence of potential interest to aviation, confirming conclusions reached by earlier pioneering studies. However, to our knowledge, this important process has not received the attention it deserves by the atmospheric community so far, and therefore, it is the principal goal of this paper to not only present some observations and preliminary modeling results, but also redraw the attention of atmospheric scientists to this important process. Plain Language Summary: The free atmosphere above the planetary boundary layer is stably stratified, and therefore, turbulent mixing there is shear driven and occurs generally under the influence of stable density stratification. However, convective mixing can also occur there under certain conditions. When precipitating snow/ice particles fall below the cloud base of midlevel clouds, they can sublimate if the air column below the cloud is dry enough. The resulting cooling of the air column drives vigorous convection. This midlevel cloud‐base turbulence process is the subject of this article. Key Points: Midlevel cloud‐base turbulence observed by the MU radar in Shigaraki, Japan, during 2015 and 2016 is presented to show its ubiquitous natureA simple analytical model is presented for approximate estimation of turbulence parameters inside a MCT layerA one‐dimensional second‐moment closure‐based turbulent mixing model is applied to an MCT event observed during 2015 and results compared to observations [ABSTRACT FROM AUTHOR]

Plasma convection in the coupled inner magnetosphere‐ionosphere is influenced by different factors such as neutral winds, penetration electric fields, and polarization electric fields. Several crucial insights about the dynamics in the region have been derived by interpreting observations in conjunction with numerical simulations, and recent expansion in ground‐ and space‐based measurements in the region along with improvements in theoretical modeling has fueled renewed interest in the subject. In this paper we present a comprehensive review of the literature with an emphasis on studies since 2012 relevant to the National Science Foundation Geospace Environment Modeling program. We cover four specific areas: (1) the subauroral polarization stream, (2) penetration electric fields, (3) the disturbance dynamo, and (4) quiet time subauroral convection. We summarize new observations and resulting insights relevant to each of these topics and discuss various outstanding issues and unanswered questions. Key Points: Subauroral convection is driven by complex interactions involving neutral winds, penetration electric fields, and polarization electric fieldsKey results on subauroral convection are summarized, with an emphasis on studies related to the SIMIC focus group of the NSF GEM programModeling quiet geomagnetic conditions in conjunction with observations is necessary to understand the physics behind subauroral convection [ABSTRACT FROM AUTHOR]

The physics suite of the Community Atmosphere Model version 5 (CAM5) has recently been implemented in the Weather Research and Forecasting (WRF) model to explore the behavior of the parameterization suite at high resolution and within the controlled setting of a limited area model. The initial paper documenting this capability characterized the behavior for a northern high-latitude region. This paper characterizes the precipitation characteristics for continental, midlatitude, springtime conditions during the Midlatitude Continental Convective Clouds Experiment (MC3E) over the central United States. This period exhibited a range of convective conditions from those driven strongly by large-scale synoptic regimes to more locally driven convection. The study focuses on the precipitation behavior at 32 km grid spacing to better anticipate how the physics will behave in a global model when used at similar grid spacing in the coming years. Importantly, one change to the Zhang-McFarlane deep convective parameterization when implemented in WRF was to make the convective timescale parameter an explicit function of grid spacing. This study examines the sensitivity of the precipitation to the default value of the convective timescale in WRF, which is 600 s for 32 km grid spacing, to the value of 3600 s used for 2° grid spacing in CAM5. For comparison, a 1200 s and an infinite convective timescale are also used. The results show that the 600 s timescale gives the most accurate precipitation amount over the central United States. However, this setting has the worst precipitation diurnal cycle, with the convection too tightly linked to the daytime surface heating. Longer timescales greatly improve the diurnal cycle but result in less precipitation and produce a low bias. An analysis of rain rates shows the accurate precipitation amount with the shorter timescale is assembled from an over abundance of drizzle combined with too few heavy rain events. With longer timescales, one can improve the frequency distribution, particularly for the extreme rain rates. Ultimately, without changing other aspects of the physics, one must decide between accurate diurnal timing and rain amount when choosing an appropriate convective timescale. [ABSTRACT FROM AUTHOR]

ABSTRACT High-resolution NWP models which can explicitly allow convection (albeit poorly resolved) are usually run in limited-area domains, and are nested inside coarser resolution models with parametrized convection. The mismatch of the grids and model physics at the boundaries of the limited-area fine resolution model can be a major source of model error. Two major issues are the change in the representation of convection (parameterized to explicit) as air enters the fine resolution model and the limited boundary updating frequency. In this paper, a variable-grid, fine-resolution, limited-area version of the Met Office's Unified Model (UM), developed with the aim of addressing this and related problems with nested models is described. In this variable resolution model, the grid size varies smoothly from coarser (but still convection permitting) resolution at the outer boundaries to a uniform fine resolution in the interior of the domain. In this paper we present results from a comparison of this variable grid model with the analogous results from an equivalent nested model set with uniform high-resolution model nested inside a lower resolution one. The comparison is carried out for a number of convective cases. It is found that the variable resolution model gives very similar results to the nested model system in the inner fixed resolution part of the domain away from the boundaries, both in individual case studies and when statistics are aggregated over cases. This gives confidence in the validity of the variable resolution approach. It is shown that the variable resolution model also gives the hoped for benefits of reducing artefacts at the boundaries. [ABSTRACT FROM AUTHOR]

The field of space weather has made great strides in understanding and simulating large‐scale, global responses of the Earth's upper atmosphere to various inputs from the Sun; however, the mesoscale phenomena (~30–500 km wide) that are much more dynamic and powerful in the coupled system have remained uncharacterized. We therefore present key parameters of mesoscale ionospheric plasma flows in order to evaluate their relationship within the coupled system and to inform global models. We characterize mesoscale plasma flow properties in the nightside polar cap and auroral oval using nine years of Super Dual Auroral Radar Network (SuperDARN) line‐of‐sight velocity data from the stations at Rankin Inlet and Saskatoon. We quantify their width, velocity, occurrence rates, duration, and orientation, and how these characteristics depend on latitude, magnetic local time (MLT), season, substorm activity (AL), solar cycle (F10.7), and interplanetary magnetic field (IMF) clock angle. Measuring the ionospheric footpoint of magnetospheric fast flows, our analysis technique from the ground also provides a 2‐D picture of flows and their characteristics that spacecraft alone cannot provide. Results include a characteristic equatorward flow width of ~180 km in the polar cap and ~140–150 km in the auroral oval. Flow velocities vary under the different conditions we studied. Equatorward polar cap flows and poleward flows everywhere have a postmidnight preference, suggesting a connection to polar cap arcs. Equatorward auroral oval flows have a premidnight preference, suggesting a connection to substorm‐related phenomena. The location and orientation of mesoscale flows dependent on IMF clock angle suggests that mesoscale flows follow the large‐scale background convection. Plain Language Summary: Space weather models do well at predicting global, large‐scale phenomena in Earth's upper atmosphere based on what the solar wind is doing. However, these models miss the smaller‐scale phenomena that are very dynamic and important to the system. They get washed out by the Earth's global reaction to the Sun. It is therefore necessary to study these smaller phenomena to know how big they are, how long they last, where they occur, and under what conditions they occur. We answer these questions by using radar stations on Earth's surface to measure fast flows of charged particles in Earth's upper atmosphere. We find that flow width does not change with the changing solar wind or changing space weather—they are usually ~180 km wide in the polar cap and ~140–150 km wide in the latitudes where the aurora occur. Flow speeds do depend on space weather, though. Faster flows occur in the auroral region during big space weather events. Fast flows occur in the polar cap when the Sun is more active. These flows are oriented in the direction of the global flows that always exist in the upper atmosphere. In our paper we also relate them to other space weather phenomena. Key Points: Nine years of SuperDARN data were used to build an empirical model of mesoscale ionospheric plasma flows and their characteristicsPolar cap flows have postmidnight preference like polar cap arcs. Auroral oval flows have premidnight preference like substorm phenomenaFlow orientation dependence on IMF BY suggests that mesoscale flows have a tendency to be aligned with large‐scale background convection [ABSTRACT FROM AUTHOR]

Abstract: The pulsating aurora covers a broad range of fluctuating shapes that are poorly characterized. The purpose of this paper is therefore to provide objective and quantitative measures of the extent to which pulsating auroral patches maintain their shape, drift and fluctuate in a coherent fashion. We present results from a careful analysis of pulsating auroral patches using all‐sky cameras. We have identified four well‐defined individual patches that we follow in the patch frame of reference. In this way we avoid the space‐time ambiguity which complicates rocket and satellite measurements. We find that the shape of the patches is remarkably persistent with 85–100% of the patch being repeated for 4.5–8.5 min. Each of the three largest patches has a temporal correlation with a negative dependence on distance, and thus does not fluctuate in a coherent fashion. A time‐delayed response within the patches indicates that the so‐called streaming mode might explain the incoherency. The patches appear to drift differently from the SuperDARN‐determined E → × B → convection velocity. However, in a nonrotating reference frame the patches drift with 230–287 m/s in a north eastward direction, which is what typically could be expected for the convection return flow. [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]

This paper describes a new intermediate global atmosphere model in which synoptic and planetary dynamics including the advection of water vapor are explicit in 10 layers, the time-mean flow is centered near a realistic state through the use of carefully calibrated time-independent 3-D forcings, and temporal anomalies of convective tendencies of heat and moisture in each column are represented as a linear matrix acting on the anomalous temperature and moisture profiles. Currently, this matrix is Kuang's [2010] linear response function (LRF) of a cyclic convection-permitting model (CCPM) in equilibrium with specified atmospheric cooling (i.e., without radiation or WISHE interactions, so it conserves column moist static energy exactly). The goal of this effort is to cleanly test the role of convection's free-tropospheric moisture sensitivity in tropical waves, without incurring large changes of mean climate that confuse the interpretation of experiments with entrainment parameters in the convection schemes of full-physics GCMs. When the sensitivity to free-tropospheric moisture is multiplied by a factor ranging from 0 to 2, the model's variability ranges from: (1) moderately strong convectively coupled Kelvin waves with speeds near 20 m s-1; to (0) similar but much weaker waves; to (2) similar but stronger and slightly faster waves as the water vapor field plays an increasingly important role. Longitudinal structure in the model's time-mean tropical flow is not fully realistic, and does change significantly with matrix-coupled variability, but further work on editing the anomaly physics matrix and calibrating the mean state could improve this class of models. [ABSTRACT FROM AUTHOR]

This paper concerns a nonlinear analysis of the effects of viscoelasticity on convection in ferroliquids. We consider the Oldroyd model for the constitutive equation of the liquid. The linear stability analysis yields the critical value of the Rayleigh number for the onset of oscillatory convection in Maxwell and Jeffrey ferroliquids. The use of a minimal mode double Fourier series in the nonlinear perturbation equations yields a Khayat–Lorenz model for the ferromagnetic liquid, and that is scaled further to get the classical Lorenz model as a limiting case. The scaled Khayat–Lorenz model thus obtained is solved numerically and the solution is used to compute the time‐dependent Nusselt number, which quantifies the heat transport. The results are analyzed for the dependence of the time‐averaged Nusselt number on different parameters. [ABSTRACT FROM AUTHOR]