Understanding the moisture variance in precipitating shallow cumulus convection

  • The impact of precipitation in shallow cumulus convection on the moisture variance and third-order moments of moisture is investigated with the help of large-eddy simulations. Three idealized simulations based on the Rain in Cumulus over the Ocean field experiment are analyzed: one nonprecipitating, on a smaller domain, and two precipitating cases, on a larger domain with different initial profiles of moisture. Results show that precipitation and the associated cloud organization lead to increased generation of higher-order moments (HOM) of moisture compared to the nonprecipitating case. To understand the physical mechanism and the role of individual processes in this increase, budgets of HOM of moisture are studied. Microphysics directly decreases the generation of HOM of moisture, but this effect is not dominant. The gradient production term is identified as the main source term in the HOM budgets. The influence of the gradient production term on moisture variance is further examined separately in cloud active and nonactive regions. The main contribution to the gradient production term comes from the smaller cloud active region because of the stronger moisture flux. Further analyses of the horizontal and vertical cross sections of moisture fluctuations show that the precipitation-induced downdrafts and updrafts are the main mechanism for the generation of moisture variance. The variance increase is linked to shallow dry downdraft regions with horizontal divergence in the subcloud layer, moist updrafts with horizontal convergence in the bulk cloud layer, and finally wider areas of horizontal divergence in the cloud inversion layer.

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Author:Theethai-Jacob Anurose, Ivan Bašták Ďurán, Jürg Schmidli, Axel Seifert
Parent Title (English):JGR. Atmospheres
Place of publication:Hoboken, NJ
Document Type:Article
Date of Publication (online):2019/11/22
Date of first Publication:2019/11/22
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Release Date:2022/03/08
Tag:Atmospheric boundary layer; Large eddy simulation; Shallow cumulus convection; Turbulent budget
Issue:1, art. e2019JD031178
Page Number:20
First Page:1
Last Page:20
This study was supported by the Federal Ministry of Education and Research in Germany (Bundesministerium fr Bildung und Forschung; BMBF) through the research program High Definition Clouds and Precipitation for Climate Prediction-HD(CP)2. The simulations were performed on LOEWE supercomputing and MISTRAL, DKRZ, Hamburg, Germany. Ivan Bastak Duran and Juerg Schmidli were supported by the Hans Ertel Centre for Weather Research.
The data for this study were generated with the LES model MicroHH, openly available in Zenodo at https://doi.org/10.5281/zenodo.822842 (van Heerwaarden et al., 2017b). The configuration files and output statistics of the three simulations (STD, MST, and CTRL) are openly available in Zenodo at http://doi.org/10.5281/zenodo.3472616 (Bastak Duran et al., 2019).
Institutes:Geowissenschaften / Geographie
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 55 Geowissenschaften, Geologie / 550 Geowissenschaften
Licence (German):License LogoCreative Commons - Namensnennung 4.0