Toward parametrization of precipitating shallow cumulus cloud organization via moisture variance

  • The influence of the initial vertical moisture profile on precipitating shallow cumulus cloud organization in terms of the column-averaged moisture variance is investigated using large-eddy simulations. Five idealized simulations based on the Rain in Cumulus over the Ocean field experiment with different initial moisture profiles are investigated. All cases simulate precipitating shallow cumulus convection in a marine sub-tropical region under large-scale subsidence. The results show that the moisture variance is mainly generated through the interaction of the moisture flux and the moisture gradient in the gradient production term at the top of the boundary layer. The development is characterized by three regimes: initial, transition, and quasi-steady regime. During the initial regime, the moisture gradient is built up by moisture accumulation until precipitating convection starts. Within the transition regime, precipitation enables mesoscale cloud organization with enhanced convective activity and moisture fluxes. The moisture variance increases from the moist to the dry initial moisture profiles. In a following quasi-steady regime, the moisture variance is approximately preserved. Thereby, the initial moisture gradient between the average sub-cloud layer and the free atmosphere is found to be an important factor for the generation of the quasi-steady column-averaged moisture variance. The result suggests that a resolved-scale variable like the moisture gradient can be used to estimate the quasi-steady state conditions resulting from cloud organization. This finding may serve as a starting point for the parametrization of the subgrid scale cloud organization caused by precipitating shallow convection.
Author:Marius Levin Thomas, Ivan Bašták Ďurán, Jürg Schmidli
Parent Title (English):JGR : Atmospheres
Place of publication:Hoboken, NJ
Document Type:Article
Date of Publication (online):2021/07/14
Date of first Publication:2021/07/14
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Release Date:2022/03/22
Tag:atmospheric boundary layer; cloud organization; large-eddy simulation; shallow cumulus convection
Issue:15, art. e2021JD034939
Page Number:14
First Page:1
Last Page:14
This research was funded by Hans Ertel Centre for Weather Research of DWD (3rd phase, The Atmospheric Boundary Layer in Numerical Weather Prediction) grant number 4818DWDP4. This work used resources of the Deutsches Klimarechenzentrum (DKRZ) granted by its Scientific Steering Committee (WLA) under project ID bb1096. Open access funding enabled and organized by Projekt DEAL.
Institutes:Geowissenschaften / Geographie
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 55 Geowissenschaften, Geologie / 550 Geowissenschaften
Licence (German):License LogoCreative Commons - Namensnennung 4.0