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In the past decade, dynamical downscaling using "pseudo‐global‐warming" (PGW) techniques has been applied frequently to project regional climate change. Such techniques generate signals by adding mean global climate model (GCM)‐simulated climate change signals in temperature, moisture, and circulation to lateral and surface boundary conditions derived from reanalysis. An alternative to PGW is to downscale GCM data directly. This technique should be advantageous, especially for simulation of extremes, since it incorporates the GCM's full spectrum of changing synoptic‐scale dynamics in the regional solution. Here, we test this assumption, by comparing simulations in Europe and Western North America. We find that for warming and changes in temperature extremes, PGW often produces similar results to direct downscaling in both regions. For mean and extreme precipitation changes, PGW generally also performs surprisingly well in many cases. Moisture budget analysis in the Western North America domain reveals why. Large fractions of the downscaled hydroclimate changes arise from mean changes in large‐scale thermodynamics and circulation, that is, increases in temperature, moisture, and winds, included in PGW by design. The one component PGW may have difficulty with is the contribution from changes in synoptic‐scale variability. When this component is large, PGW performance could be degraded. Global analysis of GCM data shows there are regions where it is large or dominant. Hence, our results provide a road map to identify, through GCM analyses, the circumstances when PGW would not be expected to accurately regionalize GCM climate signals. Plain Language Summary: Simulation of regional climate change requires regional climate models, given that global models cannot adequately represent local climate. Two techniques are typically employed for this purpose. In the first, known as direct downscaling, future climate simulated by a global model is fed to a regional model over the domain of interest. In the second, known as pseudo global warming (PGW), large‐scale observations of current climate are perturbed by the global model's future changes, and then fed to the regional model. Direct downscaling appears advantageous because it is more physically consistent with the global model. We test this idea by comparing these two techniques over both Western North America and Europe. They produce surprisingly similar temperature and precipitation projections in both regions. The reason for this similarity is investigated by analyzing the model physics in Western North America. We show there is one component, representing changes to individual storms, that PGW may have difficulty representing. PGW succeeds because this component makes a small contribution in Western North America. But there are other regions where it makes a larger or dominant contribution. In such regions, regional modeling using PGW may produce errors in simulating regional climate change. Key Points: Pseudo global warming and direct dynamical downscaling produce generally similar regional projections over Western North America and EuropeFirst‐order moisture budget terms determining future hydroclimate change are similar between the two techniquesRegions whose hydroclimates are dominated by higher‐order moisture budget terms require evaluation prior to downscaling [ABSTRACT FROM AUTHOR]

This work explores the impact of rotation on tropical convection and climate. As our starting point, we use the RCEMIP experiments as control simulations and run additional simulations with rotation. Compared to radiative convective equilibrium (RCE) experiments, rotating RCE (RRCE) experiments have a more stable and humid atmosphere with higher precipitation rates. The intensity of the overturning circulation decreases, water vapor is cycled through the troposphere at a slower rate, the subsidence fraction decreases, and the climate sensitivity increases. Several of these changes can be attributed to an increased flux of latent and sensible heat that results from an increase of near‐surface wind speed with rotation shortly after model initialization. The increased climate sensitivity results from changes of both the longwave cloud radiative effect and the longwave clear‐sky radiative fluxes. This work demonstrates the sensitivity of atmospheric humidity and surface fluxes of moisture and temperature to rotation. Plain Language Summary: Many useful studies of the tropical regions of Earth have neglected to include rotation; however, phenomena such as tropical cyclones and atmospheric waves are fundamentally tied to rotation. This work compares models of the tropics with and without rotation. Compared to experiments without rotation, rotating experiments have a more humid and stable atmosphere. Although water vapor is cycled through the atmosphere at a slower rate, the precipitation rate increases. The climate sensitivity also increases due to changes in both clouds and water vapor. Many of these changes are the result of increased wind speeds. We argue that idealized modeling of Earth's tropical regions should include not just stationary experiments but also experiments that include rotation. Key Points: Rotation leads to a decreased intensity of the overturning circulation but increased mean precipitation and precipitable waterStatic stability increases with rotation, net radiative cooling remains approximately constant, resulting in a smaller subsidence velocityRotating experiments have a larger effective climate sensitivity relative to RCE experiments mostly due to longwave radiative changes [ABSTRACT FROM AUTHOR]

Organized mesoscale convective systems (MCSs) contribute a significant amount of precipitation in the Central and Eastern US during spring and summer, which impacts the availability of freshwater and flooding events. However, current global Earth system models cannot capture MCSs well and misrepresent the statistics of precipitation in the region. In this study, we investigate the representation of MCSs in three configurations of the Energy Exascale Earth System Model (E3SMv1) by tracking individual storms based on outgoing longwave radiation using a new application of TempestExtremes. Our results indicate that conventional parameterizations of convection, implemented in both low (LR; ∼150 km) and high (HR; ∼25 km) resolution configurations, fail to capture almost all MCS‐like events, in‐part because they underestimate high‐level cloud ice associated with deep convection. On the other hand, the multiscale modeling framework (MMF; cloud‐resolving models embedded in each grid‐column of ∼150 km resolution E3SMv1) configuration represents MCSs and their annual cycle better. Nevertheless, relative to observations, the E3SMv1‐MMF spatial distribution of MCSs and associated precipitation is shifted eastward, and the diurnal timing is lagged. A comparison between the large‐scale environment in E3SMv1‐MMF and ERA5 reanalysis suggests that the biases during the summer in E3SMv1‐MMF are associated with biases in low‐level humidity and meridional moisture transport within the low‐level jet. The fact that conventional parameterizations of convection, even with high‐resolution, cannot capture MCSs over the US suggests that methods with explicit representation of kilometer‐scale convective organization, such as the MMF, may be necessary for improving the simulation of these convective systems. Plain Language Summary: Organized thunderstorms, known as mesoscale convection systems (MCSs), can contribute to large amounts of rainfall and flooding in the United States, especially during the summer and spring. However, current Earth system models have difficulties representing the complex physical processes that are important to these storm systems, which occur at smaller scales than the models resolve. In this study, we assess the ability of the Energy Exascale Earth System Model v1 to simulate MCSs using two advanced configurations (high‐resolution and multiscale modeling framework), and compare to the conventional low‐resolution configuration and observations. To identify MCS‐like events, we implemented a tracking method based on only the outgoing longwave radiation, which we apply to assess MCS characteristics and associated precipitation. Our results suggest conventionally parameterized configurations, with low‐ (∼150 km) and high‐ (∼25 km) resolution grids, fail to capture MCSs, due in part to an under‐simulation of high‐level cloud ice. On the other hand, the multiscale modeling framework configuration (i.e., kilometer‐scale cloud‐resolving models embedded in a standard ∼150 km resolution global grid) better simulates MCSs and related characteristics. Nevertheless, we identify biases in the location and timing of simulated MCSs and associated rainfall, which can be linked to biases in simulating the large‐scale environment during summer. Key Points: Energy Exascale Earth System Model (E3SMv1) with conventional parameterizations of convection underestimates high‐level cloud ice and fails to capture spring and summer mesoscale convective systems (MCSs)E3SMv1 with the MMF configuration captures MCSs, but has some biases, including an eastward shift in location and lag in diurnal timingE3SMv1‐MMF MCS‐precipitation biases are linked to biases in low‐level humidity and moisture transport associated with the low‐level jet [ABSTRACT FROM AUTHOR]

Previous work has found that as the surface warms the large‐scale tropical circulations weaken, convective anvil cloud fraction decreases, and atmospheric static stability increases. Circulation changes inevitably lead to changes in the humidity and cloud fields which influence the surface energetics. The exchange of mass between the boundary layer (BL) and the midtroposphere has also been shown to weaken in global climate models. What has remained less clear is how robust these changes in the circulation are to different representations of convection, clouds, and microphysics in numerical models. We use simulations from the Radiative‐Convective Equilibrium Model Intercomparison Project to investigate the interaction between overturning circulations, surface temperature, and atmospheric moisture. We analyze the underlying mechanisms of these relationships using a 21‐member model ensemble that includes both General Circulation Models and Cloud‐system Resolving Models. We find a large spread in the change of intensity of the overturning circulation. Both the range of the circulation intensity, and its change with warming can be explained by the range of the mean upward vertical velocity. There is also a consistent decrease in the exchange of mass between the BL and the midtroposphere. However, the magnitude of the decrease varies substantially due to the range of responses in both mean precipitation and mean precipitable water. We hypothesize based on these results that despite well understood thermodynamic constraints, there is still a considerable ability for the cloud fields and the precipitation efficiency to drive a substantial range of tropical convective responses to warming. Plain Language Summary: Tropical large‐scale overturning circulations are expected to weaken with warming. This weakening is the result of precipitation increasing at a slower rate than the atmospheric water vapor. Because precipitation and water vapor are important measures of how energy flows through the atmosphere it is important to understand how they will respond to a warming climate. We use two methods to calculate the change of the overturning circulation in 21 different simulations of the tropical atmosphere. This group of 21 models includes high resolution models that resolve cloud systems, and global models with grid‐spacing of about 100 km. We show that a weakening circulation that results from increasing atmospheric stability and increased water vapor is a robust result across most models. But across the group of models there is a large range of magnitudes in the response of the circulation to warming. This variability is well explained by the magnitude of the mean upward vertical velocity. Higher resolution models do not have a narrower range of responses. Narrowing this range of responses will depend on developing a better understanding of what drives the variations in atmospheric stability, surface fluxes of latent energy, and relative humidity. Key Points: The overturning tropical circulation weakens as the surface warms in the majority of radiative convective equilibrium models examinedInter‐model spread of circulation intensity and change of intensity are highly correlated with ascending velocity spread at 500 hPaVariability of both the clear‐sky heating and static stability result in large variations of the subsidence velocity [ABSTRACT FROM AUTHOR]

Engineered living materials (ELMs) have broad applications for enabling on‐demand bioproduction of compounds ranging from small molecules to large proteins. However, most formulations and reports lack the capacity for storage beyond a few months. In this study, we develop an optimized procedure to maximize stress resilience of yeast‐laden ELMs through the use of desiccant storage and 10% trehalose incubation before lyophilization. This approach led to over 1‐year room temperature storage stability across a range of strain genotypes. In particular, we highlight the superiority of exogenously added trehalose over endogenous, engineered production in yielding robust preservation resilience that is independent of cell state. This simple, effective protocol enables sufficient accumulation of intracellular trehalose over a short period of contact time across a range of strain backgrounds without requiring the overexpression of a trehalose importer. A variety of microscopic analysis including µ‐CT and confocal microscopy indicate that cells form spherical colonies within F127‐BUM ELMs that have variable viability upon storage. The robustness of the overall procedure developed here highlights the potential for widespread deployment to enable on‐demand, cold‐chain independent bioproduction. [ABSTRACT FROM AUTHOR]

In climate science and applications, the term "metric" is used to describe the distillation of complex, multifaceted evaluations to summarize the overall quality of a model simulation, or other data product, and/or as a means to quantify some response to climate change. Metrics provide insights into the fidelity of processes and outcomes from climate models and can assist with both differentiating models' representation of variables or processes and informing whether models are "fit for purpose." Metrics can also provide a valuable reference point for co‐production of knowledge between climate scientists and climate impact practitioners. Although continued metric developments enable model developers to better understand the impacts of decisions made in the model design process, metrics also have implications for the characterization of uncertainty and facilitating analyses of underlying physical processes. As a result, comprehensive evaluation with multiple metrics enhances usability of climate information by both scientific and stakeholder communities. This paper presents examples of insights gained from the development and appropriate use of metrics, and provides examples of how metrics can be used to engage with stakeholders and inform decision‐making. This article is categorized under:Climate Models and Modeling > Knowledge Generation with ModelsThe Social Status of Climate Change Knowledge > Climate Science and Decision MakingAssessing Impacts of Climate Change > Evaluating Future Impacts of Climate Change [ABSTRACT FROM AUTHOR]

To explore the interactions among column processes in the Community Atmosphere Model (CAM), the single‐column version of CAM (SCAM) is integrated for 1000 days in radiative‐convective equilibrium (RCE) with tropical values of boundary conditions, spanning a parameter or configuration space of model physics versions (v5 vs. v6), vertical resolution (standard and 60 levels), sea surface temperature (SST), and some interpretation‐driven experiments. The simulated time‐mean climate is reasonable, near observations and RCE of a cyclic cloud‐resolving model. Updraft detrainment in the deep convection scheme produces distinctive grid‐scale structures in humidity and cloud, which also interact with radiative transfer processes. These grid artifacts average out in multi‐column RCE results reported elsewhere, illustrating the nuts‐and‐bolts interpretability that SCAM adds to the hierarchy of model configurations. Multi‐day oscillations of precipitation arise from descent of warm convection‐capping layers starting near the tropopause, eventually reset by a burst of convective deepening. Experiments reveal how these oscillations depend critically on an internal parameter that controls the number of neutral buoyancy levels allowed for determining cloud top and computing dilute convective available potential energy in the deep convection scheme, and merely modified a little by disabling cloud‐base radiation (heating of cloud base). This strong dependence of transient behavior in 1D on this parameter will be tested in the second part of this work, in which SCAM is coupled to a parameterized dynamics of two‐dimensional, linearized gravity wave, and in the 3D simulations in future study. Plain Language Summary: Atmospheric climate models are so complicated, with so many interacting processes, that their behaviors are hard to interpret and thus flaws are hard to fix. This study tries to address that difficulty by isolating the algorithms representing vertical physical processes within an air column (turbulence, clouds, and radiation), without allowing any wind to move and smear the features caused by those interacting processes. Two versions of a popular open‐source community model are compared in this one‐dimensional single‐column framework, along with modified versions. Results suggest some ways that the model can be understood and perhaps improved, but those hypotheses need to be tested in more complicated versions of the model, accounting for winds and a spherical planet and eventually all the other complications of Earth. Key Points: Radiative‐convective equilibrium occurs in the Single Column Atmospheric ModelThe simulated climate states feature grid artifacts of humidity and cloud that are contributed from deep convective updraft detrainmentMulti‐day oscillations occur spontaneously, and are modulated by number of neutral buoyancy levels allowed for determining final cloud top [ABSTRACT FROM AUTHOR]

High‐resolution climate models (∼28 km grid spacing) can permit realistic simulations of tropical cyclones (TCs), thus enabling their investigation in relation to the climate system. On the global scale, previous works have demonstrated that the Community Atmosphere Model (CAM) version 5 presents a reasonable TC climatology under prescribed present‐day (1980–2005) forcing. However, for the Western North Pacific (WNP) region, known biases in simulated TC genesis frequency and location under‐represent the basin's dominant share in observations. This study addresses these model biases in WNP by evaluating WNP TCs in a decadal simulation, and exploring potential improvements through nudging experiments. Among the major environmental controls of TC genesis, the lack of mid‐level moisture is identified as the leading cause of the deficit in simulated WNP TC genesis over the Pacific Warm Pool. Subsequent seasonal experiments explore the effect of constraining the large‐scale environment on TC development by nudging WNP temperature field toward reanalysis at various strengths. Temperature nudging elicits a significant response in TC genesis and intensity development, as well as in moisture and convection over the Warm Pool. These responses are sensitive to the choice of nudging timescale. Overall, the nudging experiments demonstrate that improvements in the large‐scale environment can lead to improvements in simulated TCs, suggesting future model developments in relation to model physics. In this way, the potential improvements in model fidelity will contribute to the understanding of how the mean state of current or future climates may give rise to extremes such as TCs. Plain Language Summary: Climate models at high resolution (∼28 km "pixel" size) can realistically represent tropical cyclones (TCs). Previous work has shown that on the global scale, the spatial pattern and annual frequency of TC formation are well simulated in a high‐resolution climate model. However, for the typhoon‐prone Western North Pacific (WNP) region, the number of TCs as simulated by the model is much lower than observation, and the location of their formation is too much toward the north. Our study finds out that these differences between simulated and observed TCs are due to the simulated environment: over the region in the WNP where the ocean temperatures are the warmest and TCs typically form, the simulated environment is too dry and cold. To address these issues, we conducted experiments that nudge the temperature over the WNP region toward observation at various strengths. The environment, with lessened cold bias, generally becomes more moistened and gives rise to more realistic TC formation and intensity evolution. Our results suggest that by improving the simulation of the background mean state, climate models can better represent extreme events such as TCs. Key Points: In tropical cyclones (TC)‐permitting Community Atmosphere Model 5 (CAM 5), cold and dry biases over Pacific Warm Pool leads to lack of Western North Pacific (WNP) TCsConstraining WNP large‐scale environment by nudging temperature improves Warm Pool convection and the spatial distribution of TCsTC genesis and intensity development are sensitive to the choice of nudging timescale [ABSTRACT FROM AUTHOR]

While many modeling studies have attempted to estimate how tropical cyclone (TC) precipitation is impacted by climate change, the multitude of analysis techniques and methodologies have resulted in varying conclusions. Simplified models may be able to help overcome this problem. Radiative‐convective equilibrium (RCE) model simulations have been used in various configurations to study fundamental aspects of Earth's climate. While many RCE modeling studies have focused on TC genesis, intensification, and size, limited work has been done using RCE to study TC precipitation. In this study, the response of TC precipitation to sea surface temperature (SST) change is analyzed in global Community Atmosphere Model (CAM) aquaplanet simulations run with Radiative‐Convective Equilibrium Model Intercomparison Project protocols, with the addition of planetary rotation. We expect that the insight gained about how TC precipitation responds to SST warming will help predict how TCs in the real world respond to climate change. In the CAM RCE simulations, the warmer SST simulations have less TCs on average, but the TCs tend to be larger in outer size and more intense. As simulation SST increases, more extreme precipitation rates occur within TCs, and more of the TC precipitation comes from these extreme rates. For extreme (99th percentile) TC precipitation, SST, and TC intensity increases dominate the 8.6% per K increase, while TC outer size changes have little impact. For accumulated TC precipitation, SST, and TC intensity contributions are still the majority, but TC outer size changes also contribute to the 6.6% per K increase. Key Points: Global tropical cyclone (TC) count decreases while intensity and size increase with surface warming in radiative‐convective equilibrium simulationsMost of the TC precipitation comes from extreme rates which become more extreme with surface warmingSea surface temperature (SST) and TC intensity dominate precipitation metric change while impacts of size are metric‐dependent [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]

Tropical modes of variability, including the Madden‐Julian Oscillation (MJO) and the El Niño‐Southern Oscillation (ENSO), are challenging to represent in climate models. Previous studies suggest their fundamental dependence on zonal asymmetry, but such dependence is rarely addressed with fully coupled ocean dynamics. This study fills the gap by using fully coupled, idealized Community Earth System Model (CESM) and comparing two nominally ocean‐covered configurations with and without a meridional boundary. For the MJO‐like intraseasonal mode, its separation from equatorial Kelvin waves and the eastward propagation of its convective and dynamic signals depend on the zonal gradient of the mean state. For the ENSO‐like interannual mode, in the absence of the ocean's meridional boundary, a circum‐equatorial dominant mode emerges with distinct ocean dynamics. The interpretation of the dependence of these modes on zonal asymmetry is relevant to their representation in realistic climate models. Plain Language Summary: In Earth's tropical regions, recurring patterns—such as El Niño and atmospheric waves that come with storm clusters—have a large influence on the global weather and climate. These patterns are also challenging to represent in modern climate models. Previous studies suggest that the behavior of these patterns depends on the east‐west contrast in the Pacific ocean, but these studies typically focus on the atmosphere while ignoring relevant actions in the ocean, or vice versa. In this study, we address the question by using a state‐of‐the‐art climate model with a full‐blown atmosphere and ocean. We compare two designs with simplified continental shapes, one with east‐west contrast and the other without. The behavior of atmospheric waves is more realistic with an east‐west contrast. On the other hand, in a global ocean with no land blocking the east‐west direction and therefore no east‐west contrast, phenomena similar to El Niño can still occur around the equator, but with different ocean processes. Understanding the essential conditions for these patterns will contribute to better climate models for prediction, helping with the preparation for and mitigation of extreme weather and climate events. Key Points: Two idealized coupled models, with and without a meridional ocean boundary, show Madden‐Julian Oscillation (MJO)‐ and El Niño‐Southern Oscillation (ENSO)‐relevant modes of tropical variabilityZonal asymmetry affects the distinction of an MJO‐like intraseasonal mode from equatorial Kelvin wavesWithout the ocean's meridional boundary and the associated ENSO‐type dynamics, an interannual mode still persists around the equator [ABSTRACT FROM AUTHOR]

Idealized models can reveal insights into Earth's climate system by reducing its complexities. However, their potential is undermined by the scarcity of fully coupled idealized models with components comparable to contemporary, comprehensive Earth System Models. To fill this gap, we compare and contrast the climates of two idealized planets which build on the Simpler Models initiative of the Community Earth System Model (CESM). Using the fully coupled CESM, the Aqua configuration is ocean‐covered except for two polar land caps, and the Ridge configuration has an additional pole‐to‐pole grid‐cell‐wide continent. Contrary to most sea surface temperature profiles assumed for atmosphere‐only aquaplanet experiments with the thermal maximum on the equator, the coupled Aqua configuration is characterized by a global cold belt of wind‐driven equatorial upwelling, analogous to the eastern Pacific cold tongue. The presence of the meridional boundary on Ridge introduces zonal asymmetry in thermal and circulation features, similar to the contrast between western and eastern Pacific. This zonal asymmetry leads to a distinct climate state from Aqua, cooled by ∼2°C via the radiative feedback of clouds and water vapor. The meridional boundary of Ridge is also crucial for producing a more Earth‐like climate state compared to Aqua, including features of atmospheric and ocean circulation, the seasonal cycle of the Intertropical Convergence Zone, and the meridional heat transport. The mean climates of these two basic configurations provide a baseline for exploring other idealized ocean geometries, and their application for investigating various features and scale interactions in the coupled climate system. Plain Language Summary: Simplified climate models can improve our understanding of the Earth's climate system by stripping down its complexities. For example, atmospheric scientists often use idealized models with fixed sea surface temperature that is uniform in the east‐west direction. Meanwhile, oceanographers often use box‐shaped models driven by fixed wind. Although simplified models with full atmosphere‐ocean interactions are few, previous studies have shed light on fundamental processes governing Earth's climate, including the poleward transport of energy. However, the coarse "pixel size" and overly reduced components are hard to relate to contemporary models for international climate assessments. To bridge this gap, we present two simplified models within components and resolution similar to that of state‐of‐the‐art climate models. The nominally ocean‐covered model, without continents blocking the east‐west direction, develops a global cold belt of upwelling around the equator. In contrast, the model with an additional pole‐to‐pole strip continent is more Pacific‐like with a western pool and eastern cold tongue. While broadly consistent with previous works, these new models show more details in the tropical region that affect the Hadley cells and rainfall. The capability of these simplified models is promising for addressing atmosphere‐ocean interactions of scientific and societal interests, such as El Niño and hurricanes. Key Points: Two baseline examples of fully coupled CESM with idealized ocean geometry capture many features of Earth's circulationThe nominally ocean‐covered coupled model has a global cold belt of equatorial upwelling and corresponding "reverse Hadley" cellsThe addition of a pole‐to‐pole strip continent leads to zonal asymmetry that makes the model's circulation more Pacific‐like [ABSTRACT FROM AUTHOR]

Advances in high‐performance computing make it possible to run atmospheric general circulation models (AGCMs) over an increasingly wider range of grid resolutions, using either globally uniform or variable‐resolution grids. In principle, this is an exciting opportunity to resolve atmospheric process and scales in a global model and in unprecedented detail, but in practice this grid flexibility is incompatible with the non‐ or weakly converging solutions with increasing horizontal resolution that have long characterized AGCMs. In the the Community Atmosphere Model (CAM), there are robust sensitivities to horizontal resolution that have persisted since the model was first introduced over thirty years ago; the atmosphere progressively dries and becomes less cloudy with resolution, and parametrized deep convective precipitation decreases at the expense of stratiform precipitation. This study documents a convergence experiment using CAM, version 6, and argues that a unifying cause, the sensitivity of resolved dynamical modes to native grid resolution, feeds back into other model components and explains these robust sensitivities to resolution. The increasing magnitudes of resolved vertical velocities with resolution are shown to fit an analytic scaling derived for the equations of motion at hydrostatic scales. This trend in vertical velocities results in an increase in resolved upward moisture fluxes at cloud base, balanced by an increase in stratiform precipitation rates with resolution. Compensating, greater magnitude subsiding motion with resolution has previously been shown to dry out the atmosphere and reduce cloud cover. Here, it is shown that both the increase in condensational heating from stratiform cloud formation and greater subsidence drying contribute to an increase in atmospheric stability with resolution, reducing the activity of parametrized convection. The impact of changing the vertical velocity field with native grid resolution cannot be ignored in any effort to recover convergent solutions in AGCMs, and, in particular, the development of scale‐aware physical parametrizations. [ABSTRACT FROM AUTHOR]

The Radiative‐Convective Equilibrium Model Intercomparison Project (RCEMIP) is an intercomparison of multiple types of numerical models configured in radiative‐convective equilibrium (RCE). RCE is an idealization of the tropical atmosphere that has long been used to study basic questions in climate science. Here, we employ RCE to investigate the role that clouds and convective activity play in determining cloud feedbacks, climate sensitivity, the state of convective aggregation, and the equilibrium climate. RCEMIP is unique among intercomparisons in its inclusion of a wide range of model types, including atmospheric general circulation models (GCMs), single column models (SCMs), cloud‐resolving models (CRMs), large eddy simulations (LES), and global cloud‐resolving models (GCRMs). The first results are presented from the RCEMIP ensemble of more than 30 models. While there are large differences across the RCEMIP ensemble in the representation of mean profiles of temperature, humidity, and cloudiness, in a majority of models anvil clouds rise, warm, and decrease in area coverage in response to an increase in sea surface temperature (SST). Nearly all models exhibit self‐aggregation in large domains and agree that self‐aggregation acts to dry and warm the troposphere, reduce high cloudiness, and increase cooling to space. The degree of self‐aggregation exhibits no clear tendency with warming. There is a wide range of climate sensitivities, but models with parameterized convection tend to have lower climate sensitivities than models with explicit convection. In models with parameterized convection, aggregated simulations have lower climate sensitivities than unaggregated simulations. Plain Language Summary: This study investigates tropical clouds and climate using results from more than 30 different numerical models set up in a simplified framework. The data set of model simulations is unique in that it includes a wide range of model types configured in a consistent manner. We address some of the biggest open questions in climate science, including how cloud properties change with warming and the role that the tendency of clouds to form clusters plays in determining the average climate and how climate changes. While there are large differences in how the different models simulate average temperature, humidity, and cloudiness, in a majority of models, the amount of high clouds decreases as climate warms. Nearly all models simulate a tendency for clouds to cluster together. There is agreement that when the clouds are clustered, the atmosphere is drier with fewer clouds overall. We do not find a conclusive result for how cloud clustering changes as the climate warms. Key Points: Temperature, humidity, and clouds in radiative‐convective equilibrium vary substantially across modelsModels agree that self‐aggregation dries the atmosphere and reduces high cloudinessThere is no consistency in how self‐aggregation depends on warming [ABSTRACT FROM AUTHOR]

Decreasing climate models' grid spacing improves the representation of tropical cyclones at decadal time scales. In this study, a variable‐resolution (VR) version of the Community Atmosphere Model 5 (CAM5‐VR) is utilized to study North Atlantic tropical cyclone climatology in ensemble historical climate simulations and under two Representative Concentration Pathway (RCP) projections (RCP4.5 and RCP8.5). Basin‐wide tropical cyclone counts decrease in the RCP simulations, although landfalling storm counts do not show as straightforward of a pattern, especially when focusing on regional changes. Lifetime maximum intensity metrics suggest that tropical cyclones increase in strength in the RCP ensembles. However, despite increases in tropical cyclone‐related precipitation rates and the amount of precipitation produced per storm with warming, the annual average Rx5day from tropical cyclones over the eastern United States decreases due to less landfalling storms. This work is part of a continued effort to quantify how tropical cyclone‐induced hazards may change in future climates. Plain Language Summary: Landfalling tropical cyclones create dangerous conditions for residents of the eastern United States through heavy rainfall, strong winds, and storm surge. This work utilizes a global climate model to estimate how these hazards from such storms might change in the future by studying changes in the tropical cyclones' intensities, sizes, and rainfall accumulations. In these climate model simulations, the number of tropical cyclones in the North Atlantic decreases and so does the number of tropical cyclones that make landfall in the United States in the future climate projections. The average intensities of these storms increase. The rainfall intensities within the tropical cyclones also increase in the future climate projections, so that the amount of rainfall produced per storm increases. Based on our simulations, although the number of tropical cyclones that make landfall in the United States will decrease in the future, the amount of precipitation that each landfalling storm produces will increase. Key Points: North Atlantic tropical cyclone frequency decreases and median intensity increases in future CAM5 climate change projection simulationsDue to less tropical cyclone landfalls in the United States, tropical cyclone precipitation over land decreases in CAM5 in the futureHigher precipitation rates in future climate projections increase the amount of precipitation produced per hour of tropical cyclone impact [ABSTRACT FROM AUTHOR]

A new method to construct a horizontal resolution‐dependent wind speed adjustment factor for evaluating tropical cyclones (TCs) in global climate models (GCMs) is presented. In contrast to the previous studies that used idealized axisymmetric wind fields, this study analyzes 48 hr of 10‐s surface wind fields from 1‐km TC simulations. The adjustment factor is derived from filtering the simulated TC wind fields onto various horizontal grid spacings typical of those used in GCMs. The new adjustment factor leads to TCs with greater intensity than the existing adjustment factors for horizontal grid spacings smaller than 30 km. This difference is attributed to more realistic wind fields in the TC simulations that contain highly asymmetric, localized patches of higher wind speeds instead of axisymmetric wind fields. Applying the new adjustment factor to select GCM simulations suggests the common interpretation of low‐intensity bias in GCM‐simulated TCs might be slightly exaggerated. Plain Language Summary: It has long been recognized that the intensity of tropical cyclones (maximum sustained surface wind speed) in global climate model simulations needs adjustments as the horizontal grid spacing of the climate models is not yet fine enough, resulting in the representative errors in the simulated tropical cyclone structures. This study presents a new method to construct a horizontal resolution‐dependent tropical cyclone intensity adjustment factor that can be used when evaluating tropical cyclones in climate model simulations. Our new method uses tropical cyclone simulations performed with 1‐km horizontal grid spacing, in which tropical cyclone structures are realistically captured. Applying the new adjustment factor increases the interpreted intensity of simulated tropical cyclones, which suggests that the common interpretation of low‐intensity bias in climate model‐simulated tropical cyclones in comparison to the observations might be slightly exaggerated. Key Points: A new method of constructing a tropical cyclone intensity adjustment factor for global climate model simulations is proposedThe new intensity adjustment factor uses high‐resolution tropical cyclone simulations and is horizontal resolution‐dependentUsing the new adjustment indicates the low‐intensity bias in global climate model‐simulated tropical cyclones might be slightly exaggerated [ABSTRACT FROM AUTHOR]

This paper describes the implementation of a coarser‐resolution physics grid into the Community Atmosphere Model (CAM), containing 59 fewer grid columns than the dynamics grid. The dry dynamics is represented by the spectral element dynamical core, and tracer transport is computed using the Conservative Semi‐Lagrangian Finite Volume Method (CAM‐SE‐CSLAM). Algorithms are presented that map fields between the dynamics and physics grids while maintaining numerical properties ideal for atmospheric simulations such as mass conservation and mixing ratio shape and linear‐correlation preservation. The results of experiments using the lower‐resolution physics grid are compared to the conventional method in which the physics and dynamical grids coincide. The lower‐resolution physics grid provides a volume mean state to the physics computed from an equal sampling of the different types of nodal solutions arising in the spectral‐element method and effectively mitigates grid imprinting in regions with steep topography. The impact of the coarser‐resolution physics grid on the resolved scales of motion is analyzed in an aquaplanet configuration, across a range of dynamical core grid resolutions. The results suggest that the effective resolution of the model is not degraded through the use of a coarser‐resolution physics grid. Since the physics makes up about half the computational cost of the conventional CAM‐SE‐CSLAM configuration, the coarser physics grid may allow for significant cost savings with little to no downside. Key Points: A lower‐resolution finite‐volume physics grid is implemented into CAM‐SE‐CLAM, containing 59 fewer grid columns than the dynamical coreGrid imprinting from the spectral‐element method is mitigated in regions with steep terrain, using the coarser physics gridThe coarser physics grid does not degrade the effective resolution of the model [ABSTRACT FROM AUTHOR]

The relationship between African dust and the climatology of tropical cyclones (TCs) in the North Atlantic is explored using the Community Atmosphere Model at a global horizontal resolution of 28 km. A simulation in which the aerosol model is modified to significantly reduce the amount of airborne dust is compared to a standard simulation. The simulation with reduced dust increases TC frequency globally, with the largest increase occurring in the North Atlantic. The increase in TC activity in the North Atlantic is consistent with an environment that is more conducive for the genesis and intensification of storms. TCs are more frequent (27%) and on average significantly longer lived (13%) in the low dust configuration but only slightly stronger (3%). This results in a 57% increase in accumulated cyclone energy per hurricane season on average. This work has implications for projections of future climate and resulting changes in TC activity. Plain Language Summary: Dust from the Sahara desert in Africa can impact hurricane formation and development in the North Atlantic. Carried by the wind over the North Atlantic and around the globe, the dust contributes to dry and stable air that can make it harder for thunderstorms over the ocean to develop into stronger tropical cyclones or hurricanes. In this study, we look at how this effect shows up in a climate model with sufficient resolution to represent hurricanes. After the control experiment (1980–2012), we reduced the amount of airborne dust in the model over the same historical period as a low dust experiment. In the low dust simulation, tropical cyclone frequency increases globally. In the North Atlantic where storms can be impacted directly by African dust, storms become more frequent, longer lived, and slightly stronger, increasing their destructive potential. Understanding how dust interacts with tropical cyclones in climate models will help us understand and prepare for the potential changes in hurricanes of the future. Key Points: Global and North Atlantic TC counts increase in a CAM5 global simulation with a large reduction in dustThe increase in North Atlantic TC genesis activity in the low dust simulation is consistent with the change in the genesis potential indexSimulated TCs are more intense and longer in duration in the low dust configuration [ABSTRACT FROM AUTHOR]

The Dynamical Core Model Intercomparison Project (DCMIP) provides a set of tests and procedures designed to facilitate development and intercomparison of atmospheric dynamical cores in general circulation models (GCMs). Test category 1 examines the advective transport of passive tracers by three-dimensional prescribed wind velocity fields, on the sphere. These tests are applied to the Spectral Element (SE) dynamical core of the Community Atmosphere Model (CAM), the default for high-resolution simulations in the Community Earth System Model (CESM). Test case results are compared with results from the CAM-FV (Finite Volume) and MCore models where possible. This analysis serves both to evaluate the performance of CAM-SE's spectral-element tracer transport routines as well as to provide a baseline for comparison with other atmospheric dynamical cores and f or future improvements to CAM-SE itself. [ABSTRACT FROM AUTHOR]

A standard atmospheric general circulation model is run in a uniformly rotating global radiative-convective equilibrium configuration to explore the equilibrium state, including the statistics of its constituent tropical cyclones, and its sensitivity to horizontal resolution. The Community Atmosphere Model 5 (CAM5) is run at the conventional resolution of approximately 100 km grid spacing and a high resolution of 25 km grid spacing globally. The setup uses an aqua-planet configuration with spatially uniform, diurnally varying insolation, uniform fixed sea surface temperatures, and a uniform rotation rate equal to that at 10°N. The resulting state is one in which tropical cyclones fill the global domain, such that storm count and outer storm size covary strongly. At higher resolution, the storm inner core is more intense and compact but the size of the outer circulation decreases only marginally, and storm count increases in a manner consistent with this decrease in size. Furthermore, the size of the wind field and precipitation fields are highly correlated. A simple analytical model is found to robustly reproduce the radial structure of the broad outer storm circulation. Finally, the minimum central pressure is demonstrated to be an exclusive function of peak azimuthal-mean wind speed and outer storm size. Despite significant changes in the statistics of storm count, intensity, and structure, the mean environment, including the potential intensity, is nearly identical for both simulations. Results are compared with the nonrotating case from a prior study, and a generalized conceptual framework for the interpretation of aggregation with or without rotation is proposed. [ABSTRACT FROM AUTHOR]

We present an analysis of version 5.1 of the Community Atmospheric Model (CAM5.1) at a high horizontal resolution. Intercomparison of this global model at approximately 0.25°, 1°, and 2° is presented for extreme daily precipitation as well as for a suite of seasonal mean fields. In general, extreme precipitation amounts are larger in high resolution than in lower-resolution configurations. In many but not all locations and/or seasons, extreme daily precipitation rates in the high-resolution configuration are higher and more realistic. The high-resolution configuration produces tropical cyclones up to category 5 on the Saffir-Simpson scale and a comparison to observations reveals both realistic and unrealistic model behavior. In the absence of extensive model tuning at high resolution, simulation of many of the mean fields analyzed in this study is degraded compared to the tuned lower-resolution public released version of the model. [ABSTRACT FROM AUTHOR]

The global characteristics of tropical cyclones (TCs) simulated by several climate models are analyzed and compared with observations. The global climate models were forced by the same sea surface temperature (SST) fields in two types of experiments, using climatological SST and interannually varying SST. TC tracks and intensities are derived from each model's output fields by the group who ran that model, using their own preferred tracking scheme; the study considers the combination of model and tracking scheme as a single modeling system, and compares the properties derived from the different systems. Overall, the observed geographic distribution of global TC frequency was reasonably well reproduced. As expected, with the exception of one model, intensities of the simulated TC were lower than in observations, to a degree that varies considerably across models. [ABSTRACT FROM AUTHOR]

This paper explores the evolution of idealized tropical cyclones in the Community Atmosphere Model CAM 5 with the spectral element (SE) dynamical core at grid spacings of 111, 55 and 28 km. Over 10 simulation days the storms become increasingly intense and compact with increasing resolution. The experiments reveal unrealistically strong tropical cyclone intensities of minimum surface pressures ranging from 845 to 865 hPa and absolute maximum wind speeds greater than 100 m s−1 at the highest resolution, especially when small physics time steps are used. This unphysical behavior is related to the manner in which the physics time step is applied in CAM 5. The analysis indicates that the behavior of the physics parameterizations, namely the partitioning between convective and large-scale precipitation, at small time steps contributes to this intensity. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]