Influence of mesoscale circulations on the formation of humidity haloes

Humidity haloes—regions of enhanced water vapour surrounding trade wind shallow cumulus clouds—can significantly influence downward longwave radiation due to their elevated moisture content compared to clear-sky conditions. Using data from the Barbados Cloud Observatory—including longwave radiation measurements and moisture profiles from the co-located CORAL LiDAR instrument—we analyze the radiative environment around clouds. After observing such humidity haloes up to a distance of 9\, km from shallow cumulus clouds, we find an average increase in downward longwave radiation due to haloes of 0.68 W \, m⁻², which is consistent with previous satellite based observational estimates. The cause of halo formation is also examined. A rough mass flux estimate suggests detrainment from a single cloud alone can't explain their formation. Our results suggest that mesoscale circulations likely play a key role in modulating moisture in the boundary layer and especially at cloud level, thus contributing to increasing humidity around clouds.