Shallow Cumulus Representation and Its Interaction with Radiation and Surface at the Convection Gray Zone

Xabier Pedruzo-Bagazgoitia*, Pedro A. Jiménez, Jimy Dudhia, Jordi Vilà-Guerau De Arellano

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

This study presents a systematic analysis of convective parameterizations performance with interactive radiation, microphysics, and surface on an idealized day with shallow convection. To this end, we analyze a suite of mesoscale numerical experiments (i.e., with parameterized turbulence). In the first set, two different convection schemes represent shallow convection at a 9-km resolution. These experiments are then compared with model results omitting convective parameterizations at 9- and 3-km horizontal resolution (gray zone). Relevant in our approach is to compare the results against two simulations by different large-eddy simulation (LES) models. Results show that the mesoscale experiments, including the 3-km resolution, are unable to adequately represent the timing, intensity, height, and extension of the shallow cumulus field. The main differences with LES experiments are the following: a too late onset, too high cloud base, and a too early transport of moisture too high, overestimating the second cloud layer. Related to this, both convective parameterizations produce warm and dry biases of up to 2 K and 2 g kg−1, respectively, in the cloud layer. This misrepresentation of the cloud dynamics leads to overestimated shortwave radiation variability, both spacewise and timewise. Domain-averaged shortwave radiation at the surface, however, compares satisfactorily with LES. The shortwave direct and diffuse partition is misrepresented by the convective parameterizations with an underestimation (overestimation) of diffuse (direct) radiation both locally and, by a relative 40% (10%), of the domain average.
Original languageEnglish
Pages (from-to)2467-2483
JournalMonthly Weather Review
Volume147
Issue number7
Early online date25 Jun 2019
DOIs
Publication statusPublished - Jul 2019

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