AS2.4

Significant challenges in modelling clouds render observational data an important resource for quantifying cloud feedbacks. Here, we use data from satellite and reanalysis products to estimate tropical cloud feedbacks over a wide range of circulation regimes. We use two distinct methods, month-to-month variability and linear multi-decadal trends, to gain insight as to whether short-term feedbacks are representative of feedbacks associated with CO₂-induced warming. We also investigate the extent to which cloud feedbacks are circulation-driven by decomposing the relative contributions of circulation versus thermodynamic changes to the feedbacks in each regime. The influence of thermodynamic processes on cloud feedbacks has been shown to be dominant at large spatial scales in global climate models (Byrne and Schneider, 2018), but it is unclear whether observed feedbacks are consistent with model behaviour. A particular focus of our analysis is the effect of circulation on the tropical anvil cloud area feedback in ascending regions, as this feedback constitutes the largest source of uncertainty in the overall cloud feedback yet is relatively understudied (Sherwood et al. 2020).   

References:

• Byrne, M. P., & Schneider, T. (2018). Atmospheric dynamics feedback: Concept, simulations, and climate implications. Journal of Climate, 31(8), 3249-3264.
• Sherwood, S. C., Webb, M. J., Annan, J. D., Armour, K. C., Forster, P. M., Hargreaves, J. C., ... & Zelinka, M. D. (2020). An assessment of Earth's climate sensitivity using multiple lines of evidence. Reviews of Geophysics, 58(4), e2019RG000678.

How to cite: Van de Koot, E., Byrne, M. P., and Woollings, T.: Observed relationships between circulation and cloud feedbacks in the tropics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8819, https://doi.org/10.5194/egusphere-egu22-8819, 2022.

Cloud feedbacks remain the dominant source of uncertainty in climate model predictions of the surface warming response to increasing carbon dioxide. One cause of this uncertainty is the intimate coupling between clouds and circulation: cloud responses to circulation changes are poorly understood, the circulation changes are themselves uncertain, and the potential for changes in cloud to further influence circulation contributes further uncertainty.

Motivated by the need to better understand the coupling between clouds and circulation, this presentation describes the relationship between cloud radiative effects and circulation regime (based on vertical velocity at 500 hPa) over the tropical Pacific Ocean. Based on a combination of vertical velocity from state-of-the-art reanalyses with satellite radiation measurements, we examine how the relationship between cloud and circulation changes with spatial and temporal scale, season, and ENSO index. We then examine whether these relationships are reproduced in a range of models, ranging from high resolution idealised cloud resolving simulations to the latest CMIP6 climate simulations.

How to cite: Hill, P. and Holloway, C.: Relationships between clouds and circulation in reanalyses and climate models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9916, https://doi.org/10.5194/egusphere-egu22-9916, 2022.

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 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 (RCEMIP) 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 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 boundary layer 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.   This work implies 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.

How to cite: Silvers, L., Reed, K., and Wing, A.: The Response of the Large-Scale Tropical Circulation to Warming, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5366, https://doi.org/10.5194/egusphere-egu22-5366, 2022.

Even though the complexity and resolution of global climate models has increased over the last decades, the inter-model spread in equilibrium climate sensitivity has not narrowed. The representation of tropical and subtropical marine clouds remains a major source of uncertainty in climate models. Going to higher model resolution to explicitly resolve a larger fraction of the underlying convective circulations is the most direct way towards reducing the uncertainty associated with these clouds. Convection-resolving models (CRMs) are therefore an attractive complementary tool to study tropical cloud feedbacks. Even though decade-long global CRM simulations are not yet computationally feasible, CRMs can be used in climate applications for selected limited-area domains and periods.

Here we run 3-year-long CRM simulations with the COSMO model over the tropical-to-subtropical Atlantic. We run a control simulation to evaluate the model’s capability of representing the clouds and the radiative balance. We also run a climate change scenario simulation using the pseudo-global warming (PGW) approach to study cloud-radiative feedbacks at convection-resolving resolution.

We find a good agreement between the simulated and observed annual cycle in the top-of-the-atmosphere radiative fluxes, despite a mean bias that should be possible to reduce through model calibration. There are pronounced improvements in the CRM simulation compared to the CMIP6 models over the ITCZ and the trade-wind cumulus region, while the representation of stratocumulus clouds remains challenging also in the CRM simulation. The simulated cloud-radiative feedback is at the upper end of what the CMIP6 models predict due to a pronounced positive longwave feedback at the ITCZ caused by an increase in high clouds. The shortwave cloud-radiative feedback is moderately positive and lies well within the range of the CMIP6 models with a reduction in the low-level cloud fraction over the subtropics and a partly compensating increase in the cloud fraction at the ITCZ.

How to cite: Heim, C. and Schär, C.: Convection-resolving climate simulation of the tropical-to-subtropical Atlantic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6952, https://doi.org/10.5194/egusphere-egu22-6952, 2022.

Shallow trade cumulus clouds cool the planet and fuel the large-scale circulation. Their unknown response to climate change is a major source of uncertainty in climate projections. Differing changes in cloudiness near the base of the cumulus layer with warming control the spread in simulated trade cumulus cloud feedbacks in models, with high climate sensitivity models showing a strong negative coupling between lower-tropospheric mixing and cloudiness. However, such a mixing-desiccation mechanism has never been tested with observations. Here we present novel measurements of the convective mass flux, cloud fraction and relative humidity at cloud base from the recent EUREC⁴A field campaign and find the dynamical control of cloudiness through the mass flux to overwhelm the thermodynamic response to humidity. Because the mesoscale vertical velocity controls the mass flux as much as entrainment does, the mass flux ends up being uncorrelated to relative humidity, which opposes the mixing-desiccation hypothesis. The magnitude, variability, and coupling of mass flux and cloudiness differs drastically between climate models and the EUREC⁴A observations. Models that have particularly strong trade cumulus feedbacks tend to exaggerate the dependence of cloudiness on humidity rather than the mass flux, and also exaggerate variability in cloudiness. The process-based constraints presented here render those strongly positive trade cumulus feedbacks unrealistic, for the first time supporting and explaining a weak trade cumulus feedback at the relevant process scale.

How to cite: Vogel, R., Albright, A. L., Vial, J., George, G., Stevens, B., and Bony, S.: Mesoscale dynamics protect trade-cumulus clouds from mixing-induced desiccation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10302, https://doi.org/10.5194/egusphere-egu22-10302, 2022.

Mid-latitude marine cold air outbreaks (CAOs) occur in the post-frontal sector of extratropical cyclones. Once advected over the ocean, the marine boundary layer (MBL) quickly deepens and hosts near-overcast clouds that transition into an open-cellular cloud field downwind, mediated by a reduction in aerosol concentrations. Typically, the MBL experiences strong large-scale subsidence that is often associated with free-tropospheric (FT) dry intrusions. Apart from being relatively warm and dry, FT air may have substantially different aerosol properties and, thus, different cloud condensation nuclei (CCN) concentrations compared to the MBL.

In this study, we examine the difference between MBL and FT air by using in-situ and remote sensing observations collected during NASA's ACTIVATE (Aerosol Cloud Meteorology Interactions over the Western Atlantic Experiment) field campaign in the northwest Atlantic. Analysis of the 8 CAO flights in 2020 reveals predominantly far lesser CCN concentrations in the FT than in the MBL. We investigate one representative flight more deeply, through a fetch-dependent MBL CCN budget that has contributions from sea-surface fluxes, hydrometeor collision-coalescence, and entrainment of FT air. We find a dominant role of FT entrainment in reducing MBL CCN concentrations upwind of strong precipitation that results in cloud regime transition, consistent with satellite-retrieved gradients in droplet number concentration upwind of precipitation.

The FT circulation and its relative lack of CCN can accelerate overcast-to-broken cloud transitions, especially where MBL air is CCN-rich (e.g., near continents), and thereby dramatically reduce regional albedo.

How to cite: Tornow, F., Ackerman, A., Fridlind, A., Cairns, B., Crosbie, E., Kirschler, S., Moore, R., Robinson, C., Seethala, C., Shook, M., Voigt, C., Winstead, E., Ziemba, L., Zuidema, P., and Sorooshian, A.: Dilution of boundary layer cloud condensation nucleus concentrations by free tropospheric entrainment during marine cold air outbreaks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10285, https://doi.org/10.5194/egusphere-egu22-10285, 2022.

Cold pools are known to mediate the interactions between convective rain cells. Cold pool dynamics thus constitutes an important organizing mechanism for thunderstorms, in particular mesoscale convective systems and extreme rainfall events. Unfortunately, the observational detection of cold pools on a large scale has so far been hampered by the lack of relevant large-scale near-surface data. Unlike in numerical studies, where high-resolution near-surface fields of relevant quantities such as virtual temperature and winds are available and frequently used to detect cold pools, in observational studies cold pools are mainly identified based on surface time series. Since research vessels or weather stations measure these time series locally, the characterization of cold pools from observations is limited to regional or station-based studies. To eventually enable studies on a global scale, we here develop and evaluate a methodology for the detection of cold pools that relies only on data that (i) is globally available and (ii) has high spatio-temporal resolution. We trained convolutional neural networks to segment cold pools in cloud and rainfall fields from high-resolution cloud resolving simulation output. Such data is not only available from simulations, but also from geostationary satellites that fulfill both (i) and (ii). The networks feature a U-Net architecture, a common choice for image segmentation due to its strength in learning spatial correlations at different scales. Based on cloud and rainfall fields only, the trained networks systematically identify cold pool pixels in the simulation output. Our methodology may thus open for reliable global cold pool detection from space-borne sensors. As it also provides information on the spatial extent and the relative positioning of cold pools over time, our method may offer new insight into the role of cold pools in convective organization.

How to cite: Höller, J., Härter, J. O., and Fiévet, R.: U-Net Segmentation for the Detection of Convective Cold Pools From Cloud and Rainfall Fields, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5072, https://doi.org/10.5194/egusphere-egu22-5072, 2022.

Trade wind convection organises into a rich spectrum of spatial patterns, often in conjunction with precipitation development. This raises the question of the role of precipitation for spatial organization and vice versa. Using rain radar measurements during the EUREC⁴A field campaign we find that precipitation rates vary mainly independently from the spatial arrangement of precipitating cells. Mean precipitation increases with the size or number of cells, as it is closely related to the precipitating area. The cells’ degree of clustering, contrary, is typically greatest where the mean cell size is large and the cell number small. Consequently, scenes with a quite different spatial structure – with larger, more clustered convective structures at one time or with more numerous and distributed convective structures at another time – can have similar precipitation rates. Could spatial organization be a process to maintain precipitation rates in very different environments? We exploit large-domain realistic large eddy simulations to investigate scenes of trade wind convection that exhibit similar precipitation rates but different spatial structures. We discuss how the environment and circulation differ in these scenes and how this might necessitate different spatial structures to rain.

How to cite: Radtke, J., Naumann, A. K., Vogel, R., Hagen, M., and Ament, F.: On the relationship between precipitation and the spatial structure of trade wind convection, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7264, https://doi.org/10.5194/egusphere-egu22-7264, 2022.

Idealized simulations of the tropical atmosphere have predicted that clouds can spontaneously clump together in space, despite perfectly homogeneous settings. This phenomenon has been called self-aggregation, and results in a state where a moist cloudy region with intense deep convective storms is surrounded by extremely dry subsiding air devoid of deep clouds. We review here the main findings from theoretical work and idealized models, highlighting the physical processes believed to play a key role in convective self-aggregation. We also review the growing literature on the importance and implications of this phenomenon for the atmosphere, notably for the hydrological cycle and for precipitation extremes, in our current and in a warming climate.

How to cite: muller, C., Yang, D., Craig, G., Cronin, T., Fildier, B., Haerter, J., Hohenegger, C., Mapes, B., Randall, D., Shamekh, S., and Sherwood, S.: Spontaneous aggregation of convective storms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11607, https://doi.org/10.5194/egusphere-egu22-11607, 2022.

The representation of shallow tradewind cumulus clouds in climate models accounts for the majority of inter-model spread in climate projections,
highlighting an urgent need to understand these clouds better. In particular, their spatial organisation appears to cause a strong impact of their radiative properties and dynamical evolution. The precise mechanisms driving different forms of convective organisation which arise both in nature and in simulations are, however, currently unknown.

Using unsupervised learning for identifying regimes of convective organisation in the tropical Atlantic, we will show results from analysing: a) what the
radiative properties of different forms of organisation are, b) what atmospheric characteristics coincide with different forms of organisation and c) what transitions occur when following air-masses along Lagrangian trajectories.  Specifically, we find: a) net radiation changes significantly between different forms of organisation, b) agreement with previous studies on the importance of boundary layer wind-speed and to some degree atmospheric stability, and c) we are able to succinctly capture what transitions occur between regimes.

How to cite: Denby, L.: Properties and transitions of mesoscale convective organisation during EUREC4A using unsupervised learning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3836, https://doi.org/10.5194/egusphere-egu22-3836, 2022.

Tropical shallow convection exhibits strong variations in mesoscale organisation. Bretherton and Blossey (2017) used an LES to show how this convective organisation can be produced due to an advective feedback with mesoscale vertical motion and adjustment to a weak temperature gradient. Narenpitak et al. (2021) used an LES with forcings following a boundary-layer trajectory to simulate a case study from the EUREC4A field campaign where the clouds transition from disorganised small cumulus (sugar) to deeper more organised clouds with large detrainment layers (flowers). The LES produced a transition in cloud organisation and the main driving process was shown to be the advective feedback in mesoscale vertical motion seen in Bretherton and Blossey (2017).For comparison, we have looked at the same case study using high-resolution nested simulations with the Met Office's weather model, the UM. The UM reproduces the transition from sugar to flowers. Consistent with Narenpitak et al. (2021), the UM shows that the transition is associated with an increase in organisation and the mesoscale advective feedback is an important driving process. However, unlike the LES, the UM simulations show that the sugar clouds are already associated with a large amount of organisation. Because the mesoscale organisation is already present in the UM, the advective dispersion of mesoscale aggregation is an important process opposing aggregation during the transition from sugar to flowers, unlike in the LES.

How to cite: Saffin, L., Marsham, J., Blyth, A., and Parker, D.: Mesoscale organisation transition during the 2nd Feb EUREC4A case study simulated by a high-resolution weather model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2408, https://doi.org/10.5194/egusphere-egu22-2408, 2022.

The diurnal cycle in trade wind cloudiness has been observed to be driven by the diurnal cycle in the relative frequency of occurrence of mesoscale morphologies (i.e., Vial et al. 2021). These morphologies have been grouped based on their distinct appearance and cloud size into four categories, from small to large sizes: Sugar, Gravel, Flowers, and Fish. The diurnal cycle in cloudiness is associated with a late afternoon maximum in the smallest (Sugar) clouds which give way to clouds of larger size and vertical extent (Gravel, then Flowers) throughout the night. A remaining question is how sub-cloud dynamics evolve diurnally to facilitate this diurnal cycle in cloud morphology and thus cloudiness.

We examine the daily evolution of trade wind mesoscale morphologies with in situ observations from the 2020 joint campaign, EUREC⁴A (Elucidating the Role of Clouds–Circulation Coupling in Climate) and ATOMIC (Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign), that took place in January and February in the Northwest tropical Atlantic. Measurements from the Ronald H. Brown research vessel allow us to analyze differences in the daily evolution of boundary layer structure and dynamics between morphologies. We decompose Doppler lidar-derived mass fluxes into their vertical velocity and cloud fraction contributions and examine their effect on diurnal cloud evolution as well as their relationship to environmental controls such as surface wind speeds, energy and moisture fluxes, stability, and near-surface air properties. Relationships between environmental controls and morphologies are further extended with the long-term recorded observations at the nearby moored NTAS (Northwest Tropical Atlantic Station) buoy.

How to cite: McCoy, I. L., Zuidema, P., Baidar, S., Vial, J., Schulz, H., and Brewer, A.: The Diurnal Evolution of Controls on Trade Wind Mesoscale Morphologies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3254, https://doi.org/10.5194/egusphere-egu22-3254, 2022.

In models, a local maximum of clear-sky radiative cooling in the lower troposphere often appears as a necessary condition for the development and persistence of convective organization. However, no robust understanding has been provided for the emergence and disappearance of lower-tropospheric cooling in the atmosphere. Here we propose a theoretical characterization of clear-sky radiative cooling peaks, recently calculated from over 2,000 soundings launched during the EUREC⁴A field campaign in various patterns of shallow organization. A suite of scaling approximations are developed from simplified spectral theory to connect the longwave cooling peak to the vertical humidity structure set by convection. Its height is controlled by local maxima in the vertical gradients of water vapor path, and its magnitude is mainly controlled by the ratio between column relative humidity above and below the peak. In contrast, the value of the Planck function and the spectral width of emission only weakly vary across soundings.  Water vapor spectroscopy implies that upper-level intrusions of moist air detrained from lower latitudes can substantially dim these peaks, possibly by reducing the range of the spectrum that effectively cools to space at the level of the peak. This work motivates future modeling work, formulating the hypothesis that "Fish" patterns, which embed the widest persisting dry areas, may be the most favorable conditions for radiative processes to organize convection. If at play, this radiative feedback would maintain these patterns that are efficient at cooling the tropics, a type of "dry radiator fins" which could mitigate the risk of runaway climate states.

How to cite: Fildier, B., Muller, C., Pincus, R., and Fueglistaler, S.: Low-level radiative cooling peaks in regimes of shallow convective organization, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5574, https://doi.org/10.5194/egusphere-egu22-5574, 2022.

A growing body of evidence suggests that shallow circulations play a key role in organising trade-wind clouds at the mesoscales. In turn, many of these mesoscale circulations appear to emerge directly from the shallow convection itself. We infer a very simple model for explaining this feedback from Large-Eddy Simulations of a classical numerical experiment with minimal physics (BOMEX), which depends only on the turbulent transport of liquid water in cumulus clouds and the mean environment. Since the dominant scales of the cumulus convection driving the organisation are constrained around a kilometer, we hypothesise that simulations of the development of mesoscale cloud patterns through this mechanism are sensitive to choices in the numerical representation of the cumulus convection. We show that the timescale over which mesoscale cloud structures develop can more than double in our model, merely by modifying its grid spacing or advection schemes. Hence, rather high resolutions (<100m) or significantly improved unresolved scales models may be required to faithfully represent certain forms of trade-wind mesoscale cloud patterns in models, and to understand their influence on the cloud feedback more accurately.

How to cite: Janssens, M., Glassmeier, F., Siebesma, A. P., R. de Roode, S., C. van Heerwaarden, C., and Vilà-Guerau de Arellano, J.: Numerical choices in Large-Eddy Simulations influence their ability to represent shallow convective organisation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11839, https://doi.org/10.5194/egusphere-egu22-11839, 2022.

Satellite based hyperspectral infrared (IR) sounders like IASI, AIRS and CrIS offer a wealth of information about the atmospheric composition and vertical structure. A key quantity these instruments are able to capture is the vertical profile of water vapor in clear-sky and partly cloudy conditions. The work presented here revolves around mid tropospheric layers of increased humidity, so called Elevated Moist Layers (EMLs). EMLs frequently emerge in the vicinity of deep convection in the tropics as they are thought to originate from detrained moisture of convective plumes near the stable freezing level at around 5 km altitude. Previous retrieval case studies indicate limited retrievability of EMLs based on hyperspectral IR observations depending on the exact retrieval method, retrieval setup and the atmospheric conditions. Since EMLs severely influence the local radiation budget of the atmosphere, we need to understand what operational retrievals capture and what they may miss about EMLs.

As a starting point, we present an EML case study from the NARVAL-2 measurement campaign to directly compare IASI and AIRS retrieval products to in-situ soundings. We also introduce ERA5 as an additional reference to assess whether limitations in the retrieval product propagate to the reanalysis. As a next step, we conduct a first systematic statistical assessment of EML retrievability based on long term operational retrieval data. As reference, we use radiosonde data from the GRUAN database and ERA5. The EMLs in the different datasets are first identified by introducing smooth reference humidity profiles. The EMLs are then characterized by their layer averaged anomalous humidity, their thickness and altitude. These EML characteristics are compared statistically to assess what type of EMLs the retrievals capture well and where there might be systematic issues. We also calculate radiative heating profiles and assess the impact of EML retrievability on radiative heating.

How to cite: Prange, M., Brath, M., and Buehler, S. A.: Retrieval of Elevated Moist Layers using Hyperspectral Infrared Sounders, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7904, https://doi.org/10.5194/egusphere-egu22-7904, 2022.

The transition layer in the trades has long been observed and simulated, but its origins remain little investigated. It is often associated with an about 150 m deep layer at the top of the subcloud layer that acts as a barrier to overlying convection. Using extensive observations from the EUREC4A field campaign, we propose a reconceptualization of the transition layer. Strong jumps at the mixed layer top, as expected from the theory of cloud-free convective boundary layers, are only found rarely and when they occur, they tend to occur in large cloud-free areas. We show that small clouds with their bases around 600 m maintain the transition layer, in analogy with the maintenance of the trade-wind inversion by deeper clouds. From this analysis also emerges the potential for an alternate view of entrainment mixing, which is based on the ability to detrain condensate into the transition layer and induce gentle sinking motion through negative buoyancy. Mixed layer theory and Paluch mixing diagrams are also used to gain inferences into entrainment mixing.

How to cite: Albright, A. L., Bony, S., Stevens, B., and Vogel, R.: A new conceptual picture of the transition layer, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6458, https://doi.org/10.5194/egusphere-egu22-6458, 2022.

We find an abundance of low-level, mesoscale circulations in the atmosphere below the trade-wind inversion layer based on observations of the mesoscale atmospheric circulation taken during the EUREC4A campaign. Over time-means of 3-6 hours, the mean sub-cloud divergence anomaly correlates negatively with the mean divergence anomaly in the cloud layer. Here, the term anomaly means the deviation from the EUREC4A-wide month-long mean of divergence at the corresponding altitude. Additionally, sub-cloud divergence anomaly correlates negatively with specific humidity anomaly in the sub-cloud and cloud layers, indicating moist, convergent regimes and dry, divergent regimes. We hypothesise that the presence of shallow circulations below the inversion layer explains these associations. Our proposed mechanism of shallow circulations is that regions of ascending air are balanced by neighbouring cells of subsidence, thus creating and maintaining moist and dry regions, which reinforce the shallow circulations. We use mixed-layer theory to estimate the time-scales at which the sub-cloud layer moisture would respond to such divergence patterns. The observed relationships are also evident in reanalysis data, which further reinforce that these are indeed mesoscale features and not large-scale signals captured by the observations.

How to cite: George, G., Stevens, B., Bony, S., Vogel, R., and Naumann, A. K.: The ubiquity of shallow circulations in the trades, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13444, https://doi.org/10.5194/egusphere-egu22-13444, 2022.