Cloud growth and entrainment rates in shallow cumulus and congestus during GoAmazon 2014/2015
Poster PDF
Authors
David B. Mechem — University of Kansas
Jordan Eissner — University of Kansas
Michael Jensen — Brookhaven National Laboratory
Category
Warm low clouds, including aerosol interactions
Description
Warm, shallow clouds are responsible for a substantial portion of GCM uncertainty and divergence among model climate projections. Shallow clouds determine the thermodynamic properties of the trade wind boundary layer and precondition the lower atmosphere for deeper convective events. Over land, shallow cumulus and congestus are important stages in the formation of deep convection and the diurnal cycle in precipitation, and climate models generally demonstrate a transition to deep convection that occurs much too rapidly. For convective clouds of all depths, cloud growth and entrainment are closely intertwined. Our overarching scientific question is, “Do entrainment and detrainment rates vary across different shallow convection environments?” Our early efforts in addressing this question focus on calculating estimates of entrainment rate for shallow cumulus and congestus clouds sampled during the Green Ocean Amazon 2014/5 (GoAmazon2014/5) campaign. We apply the Jensen and Del Genio (2006) bulk method to estimate entrainment rates consistent with thermodynamic sounding profiles and cloud depth obtained from the W-band ARM cloud radar (WACR). Cloud depth was found to be strongly modulated by environmental moisture, but we find little evidence to support a dependence of entrainment rate itself on moisture, a dependence that is employed in some climate model convective parameterizations. We evaluate several commonly employed entrainment formulations in light of these observational estimates of entrainment rate.
