Formation and maintenance of subsiding shells around non‐precipitating and precipitating cumulus clouds

Abstract

A shell of subsiding air is generally known to develop around cumulus clouds and shield them from their environment. We seek here to improve our understanding of such shells by (1) revealing the detailed vertical and horizontal structure of shells surrounding both shallow and deeper clouds, and (2) identifying the mechanisms responsible for in-shell subsidence generation and maintenance. To that end, a highresolution Cloud Resolving Model simulation of the shallowto-deep convection transition over a tropical land surface is analysed with an emphasis on the clouds near environment. Shells surrounding shallow and deep clouds are found to possess surprisingly similar characteristics. Important differences are however observed near cloud top where the deepest clouds are associated with stronger subsidence and broader shells. In the convective outflow region, stronger in-shell subsidence coincides with strong buoyancy reversal, but also with strong pressure gradients naturally generated by cloud top vortex dynamics. A more delicate balance between various processes takes place below, and in-shell subsidence is only barely sustained as buoyancy reversal is largely compensated by pressure gradients. Finally, while evaporation is clearly the main source of buoyancy reversal (and therefore subsidence) everywhere around cloud edges, it is also shown that the downward transport of warmer air

Fitting Cumulus Cloud Size Distributions From Idealized Cloud Resolving Model Simulations

“…The first experiment is based on the Large‐scale Biosphere‐Atmosphere (LBA) intercomparison study (Grabowski et al., 2006), with modifications similar to Böing et al. (2012) and Savre (2021). The initial potential temperature profile is taken from Grabowski et al.…”

“…The first experiment is based on the Large-scale Biosphere-Atmosphere (LBA) intercomparison study (Grabowski et al, 2006), with modifications similar to Böing et al (2012) and Savre (2021). The initial potential temperature profile is taken from Grabowski et al (2006), while the initial moisture content is modified with a relative humidity held constant and equal to 80% between the surface and 2.5 km, and decreasing linearly to 15% up to 18 km.…”

“…Both experiments were carried out using the MISU‐MIT Cloud and Aerosol (MIMICA) model solving anelastic governing equations for potential temperature, total water mass mixing ratio and momentum (Savre, 2021; Savre et al., 2014). The numerical methods employed in both cases are similar: scalar advection uses a flux‐limited version of the Lax‐Wendroff scheme, momentum advection uses fourth order central finite differences, and time integration is performed using a second order Runge‐Kutta method.…”

The Effects of Shallow Cumulus Cloud Shape on Interactions Among Clouds and Mixing With Near‐Cloud Environments

“…The shells (the area surrounding the edge of the cloud boundary, e.g., Savre (2021)) serve as an essential interface between the clouds and their environment. They play a crucial role in cloud development and facilitate the redistribution of energy and moisture within the atmosphere (Dawe & Austin, 2011; Heus et al., 2009; Luo et al., 2021; Savre, 2021).…”

“…The shells (the area surrounding the edge of the cloud boundary, e.g., Savre (2021)) serve as an essential interface between the clouds and their environment. They play a crucial role in cloud development and facilitate the redistribution of energy and moisture within the atmosphere (Dawe & Austin, 2011; Heus et al., 2009; Luo et al., 2021; Savre, 2021). Turbulent mixing at the cloud boundaries leads to moistening of the surrounding shells (Nair et al., 2021), which can subsequently impact the evolution of cloud thermodynamic properties and precipitation efficiency (Dawe & Austin, 2012; Lasher‐Trapp et al., 2021; Liu & Hallett, 1997; Lu et al., 2016; Stirling & Stratton, 2012; Trenberth et al., 2003; Xu et al., 2022; Xue & Feingold, 2006).…”