Symmetry in mesoscale circulations explains weak impact of trade cumulus self-organisation on the radiation budget in large-eddy simulations

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Authors

Martin Janssens, Fredrik Jansson, Pouriya Alinaghi, Franziska Glassmeier, Pier Siebesma 

Abstract

We investigate if mesoscale self-organisation of trade cumuli in 150 km-domain large-eddy simulations modifies the top-of-atmosphere radiation budget relative to 10 km-domain simulations, across 77 characteristic, idealised environments. In large domains, self-generated mesoscale circulations produce fewer, larger and deeper clouds, raising the cloud albedo. Yet they also precipitate more than small-domain cumuli, drying and warming the cloud layer, and reducing the cloud cover. Consequently, the large-domains' shortwave cloud-radiative effect's cooling weakly reduces, and their clear-sky outgoing longwave radiation's cooling weakly increases, for a net cooling (-0.5 W m$^{-2}$). This cooling is generally smaller than the large-domain radiation’s sensitivity to large-scale meteorological variability, which is similar in small-domain simulations and observations. Hence, spontaneously developing mesoscale circulations do not alter weak trade-cumulus feedback estimates from small domains. We explain this with a symmetry hypothesis: ascending and descending branches of mesoscale circulations symmetrically increase and reduce cloudiness, weakly modifying the mean radiation budget.

DOI

https://doi.org/10.31223/X5BH8Q

Subjects

Physical Sciences and Mathematics

Keywords

Dates

Published: 2024-09-11 11:03

Last Updated: 2024-09-11 15:03

License

CC-BY Attribution-No Derivatives 4.0 International