@article{9151, abstract = {We investigate how mesoscale circulations associated with convective aggregation can modulate the sensitivity of the hydrologic cycle to warming. We quantify changes in the full distribution of rain across radiative‐convective equilibrium states in a cloud‐resolving model. For a given SST, the shift in mean rainfall between disorganized and organized states is associated with a shift in atmospheric radiative cooling, and is roughly analogous to the effect of a 4K SST increase. With rising temperatures, the increase in mean rain rate is insensitive to the presence of organization, while extremes can intensify faster in the aggregated state, leading to a faster amplification in the sporadic nature of rain. When convection aggregates, heavy rain is enhanced by 20‐30% and nonlinear behaviors are observed as a function of SST and strength of aggregation feedbacks. First, radiative‐ and surface‐flux aggregation feedbacks have multiplicative effects on extremes, illustrating a non‐trivial sensitivity to the degree of organization. Second, alternating Clausius‐Clapeyron and super‐Clausius‐Clapeyron regimes in extreme rainfall are found as a function of SST, corresponding to varying thermodynamic and dynamic contributions, and a large sensitivity to precipitation efficiency variations in some SST ranges. The potential for mesoscale circulations in amplifying the hydrologic cycle is established. However these nonlinear distortions question the quantitative relevance of idealized self‐aggregation. This calls for a deeper investigation of relationships which capture the coupling between global energetics, aggregation feedbacks and local convection, and for systematic tests of their sensitivity to domain configurations, surface boundary conditions, microphysics and turbulence schemes.}, author = {Fildier, Benjamin and Collins, William D. and Muller, Caroline J}, issn = {1942-2466}, journal = {Journal of Advances in Modeling Earth Systems}, keywords = {Global and Planetary Change, General Earth and Planetary Sciences, Environmental Chemistry}, number = {2}, publisher = {American Geophysical Union}, title = {{Distortions of the rain distribution with warming, with and without self‐aggregation}}, doi = {10.1029/2020ms002256}, volume = {13}, year = {2021}, } @article{9125, abstract = {This study investigates the feedbacks between an interactive sea surface temperature (SST) and the self‐aggregation of deep convective clouds, using a cloud‐resolving model in nonrotating radiative‐convective equilibrium. The ocean is modeled as one layer slab with a temporally fixed mean but spatially varying temperature. We find that the interactive SST decelerates the aggregation and that the deceleration is larger with a shallower slab, consistent with earlier studies. The surface temperature anomaly in dry regions is positive at first, thus opposing the diverging shallow circulation known to favor self‐aggregation, consistent with the slower aggregation. But surprisingly, the driest columns then have a negative SST anomaly, thus strengthening the diverging shallow circulation and favoring aggregation. This diverging circulation out of dry regions is found to be well correlated with the aggregation speed. It can be linked to a positive surface pressure anomaly (PSFC), itself the consequence of SST anomalies and boundary layer radiative cooling. The latter cools and dries the boundary layer, thus increasing PSFC anomalies through virtual effects and hydrostasy. Sensitivity experiments confirm the key role played by boundary layer radiative cooling in determining PSFC anomalies in dry regions, and thus the shallow diverging circulation and the aggregation speed.}, author = {Shamekh, S. and Muller, Caroline J and Duvel, J.‐P. and D'Andrea, F.}, issn = {1942-2466}, journal = {Journal of Advances in Modeling Earth Systems}, keywords = {Global and Planetary Change, General Earth and Planetary Sciences, Environmental Chemistry}, number = {11}, publisher = {American Geophysical Union}, title = {{Self‐aggregation of convective clouds with interactive sea surface temperature}}, doi = {10.1029/2020ms002164}, volume = {12}, year = {2020}, } @article{9126, abstract = {The goal of this study is to understand the mechanisms controlling the isotopic composition of the water vapor near the surface of tropical oceans, at the scale of about a hundred kilometers and a month. In the tropics, it has long been observed that the isotopic compositions of rain and vapor near the surface are more depleted when the precipitation rate is high. This is called the “amount effect.” Previous studies, based on observations or models with parameterized convection, have highlighted the roles of deep convective and mesoscale downdrafts and rain evaporation. But the relative importance of these processes has never been quantified. We hypothesize that it can be quantified using an analytical model constrained by large‐eddy simulations. Results from large‐eddy simulations confirm that the classical amount effect can be simulated only if precipitation rate changes result from changes in the large‐scale circulation. We find that the main process depleting the water vapor compared to the equilibrium with the ocean is the fact that updrafts stem from areas where the water vapor is more enriched. The main process responsible for the amount effect is the fact that when the large‐scale ascent increases, isotopic vertical gradients are steeper, so that updrafts and downdrafts deplete the subcloud layer more efficiently.}, author = {Risi, Camille and Muller, Caroline J and Blossey, Peter}, issn = {1942-2466}, journal = {Journal of Advances in Modeling Earth Systems}, keywords = {Global and Planetary Change, General Earth and Planetary Sciences, Environmental Chemistry}, number = {8}, publisher = {American Geophysical Union}, title = {{What controls the water vapor isotopic composition near the surface of tropical oceans? Results from an analytical model constrained by large‐eddy simulations}}, doi = {10.1029/2020ms002106}, volume = {12}, year = {2020}, }