Observations of vertical motion inside precipitating trade cumuli

Rain processes are often underrepresented in our understanding of the trade-wind layer, despite trade cumuli precipitating ~30% of the time. The vertical structure of the main building blocks of precipitating convection, namely in-cloud updrafts and downdrafts, is poorly characterized due to a lack of suitable observations. Lidars cannot penetrate deeply into clouds, and hydrometeor fall speeds dominate the mean Doppler velocity from cloud-profiling radars. Here, we retrieve the vertical air motion inside precipitating clouds by making use of the Doppler velocity spectrum from the ground-based Ka-band radars at the Barbados Cloud Observatory (BCO), using methods previously developed for stratocumuli. The resulting dataset spans more than five years (2019-2025) at high (2s) resolution and is validated against available lidar measurements. We resolve circulations at the cloud scale. Shallow precipitating cumuli feature a narrow updraft at the cloud 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. We show that deeper clouds are associated with stronger updrafts and downdrafts. Faster downdrafts are also associated with higher cloud reflectivity, suggesting that microphysical processes play a large role in determining their strength. The long record also lets us ascertain seasonal variability. Shallow precipitating cumuli feature faster updrafts in the summer trades, leading to larger and faster downdrafts than in winter. We show that the total mass flux of shallow precipitating cumuli is highly variable. Both the updraft and the downdraft mass fluxes mainly depend on the cloud fraction, but their balance hinges on the downdraft intensity. These observations can improve our understanding of tropical convection and shed light on the assumptions behind convective parametrizations and constrain cloud-resolving simulations.