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

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.