How rain shapes cloud-scale dynamics and mass flux in the trades

Abstract. Trade wind cumuli often precipitate, but the effect of rain processes on their dynamics and organization is still poorly understood. Previous observations of the vertical wind inside clouds were limited to non-precipitating conditions because the mean Doppler velocity from cloud radars is dominated by hydrometeor motion in precipitating clouds. Here, we retrieve the vertical air motion inside precipitating clouds by using the Doppler velocity spectrum from the ground-based Ka-band radars at the Barbados Cloud Observatory. We validate it against available lidar measurements. We combine the in-cloud radar-derived wind with lidar observations outside of clouds into a unified dataset spanning six years (2019–2025) at high (2s) resolution. We show that precipitating cumuli act as shallow squall lines, as predicted by recent large-eddy simulations. These clouds feature a narrow updraft at the gust front that develops up to cloud top. The wider precipitation downdraft is triggered slightly below cloud top, where the rain content is large enough, and extends down to the surface where it forms a cold pool. We show that updrafts and downdrafts contribute nearly equally to the cloud base mass flux. Their balance hinges on the downdraft intensity, likely controlled by microphysical processes. These observations can improve our understanding of tropical convection, shed light on the assumptions behind convective parameterizations and constrain cloud-resolving simulations.