Mesoscale cloud cellular organization of marine stratocumulus. Part I: The dominant impact of vertical moisture gradient on drizzling stratocumulus organization
Authors
Xiaoli Zhou — NOAA/CIRES
Andrew Ackerman — NASA - Goddard Institute for Space Studies
Ann M. Fridlind — NASA - Goddard Institute for Space Studies
Pavlos Kollias — Stony Brook University
Category
Warm low clouds, including aerosol interactions
Description
This study investigates the mechanisms of mesoscale variability of drizzling stratocumulus using eddy-permitting simulations. Results show that precipitation tends to increase horizontal cloud scales via raindrop evaporation, which helps to maintain moisture stratification and sub-cloud cold/moist pools. A study of the terms in the prognostic equation for total water mixing ratio variance shows the critical impact of the moisture stratification on cloud scales. This hypothesis is supported by simulations in which thermodynamics profiles are nudged to their initial well-mixed state, which reduces cloud scales. Surprisingly, we found that sub-cloud cold/moist pools tend to respond to, rather than determine, the cloud mesoscale variability. Our results suggest that negative moisture gradient increases cloud scales by increasing moisture and latent heating in the updraft, both of which increases buoyancy in the updraft and favors a greater horizontal scale. In the presence of moist process, the dynamic effect of latent heating is found to be critical.
