From Shadow to Fertilizer: Slanted Sunlight in 3D Radiation Enhances Cloud Condensate, Size, and Lifetime of Shallow Cumulus

Abstract The impact of three‐dimensional (3D) shortwave radiation on cloud condensate, size and lifetime is investigated using large‐eddy simulations coupled to an interactive land surface model (LSM). Results show 3D radiation produces higher cloud tops and greater cloud condensate than 1D radiation, resulting from larger downward shortwave fluxes beneath clouds. The enhanced radiative flux leads to increased surface temperature, which in turn amplifies sensible and latent heat fluxes beneath clouds by about 40%, thereby promoting further cloud development. 3D radiation produces larger and longer‐lived clouds than 1D radiation, with the tail in size distribution occurring near 1,400 m in 3D‐LSM versus 1,100 m in 1D‐LSM. These differences arise from the contrasting surface heterogeneity induced by the 1D and 3D radiation schemes. Unlike 1D‐LSM, where cloud shadows fall directly beneath clouds and locally suppress updrafts, 3D‐LSM displaces shadows, favoring cloud‐scale circulations that provide positive feedback, leading to thicker, larger, and longer‐lived clouds.