Sub-cloud layer winds in the vicinity of trade-wind cumulus

Sailors have long used cumulus clouds to guide their ships into areas of favourable winds. On the upwind side of cumulus clouds, the clouds’ thermal circulation would add momentum to the prevailing flow, while on the downwind side, the opposing branch of the circulation would reduce the flow. In this study, we take a simple approach to evaluating this sailors’ theorem and visualise the winds in the sub-cloud layer in the vicinity of shallow cumulus clouds. This is done by collocating cloud radar and wind lidar profiling measurements during EUREC4A on board the RV Meteor and at the BCO for a six-month period. Is there evidence for a thermal circulation in the wind surrounding clouds, or for plume-like structures that support a mass-flux approach? We will discuss our findings for clouds of increasing depth, for which clustered convection and cold pool gustiness become increasingly important.