Radar observations of vortex-ring entrainment patterns in cumulus clouds

Recent studies have explored the existence and characteristics of vortex-ring type structures in the ascending cumulus towers. Such cloud top circulations are important because they are thought to be key players in the entrainment mechanisms. The single-Doppler vertical velocity data from the Wyoming Cloud Radar for numerous cumulus penetrations are composited to study the cumulus cloud-top circulation pattern. The cumuli were sampled in environments in two regions: the Sonoran Desert during the monsoon, and the arid high plains of Wyoming in summer. The composite analysis shows clear evidence of an updraft/downdraft dipole near cloud top, consistent with a vortex-ring circulation. The stratification of all Cu samples shows that the vortex-ring patterns tend to be found more frequently in positively buoyant cumuli with rising motion than negatively buoyant cumuli with sinking motion. Wind shear has important effect on the entrainment pattern: the vortex-ring circulations tend to be advected to the downshear side of the cloud. These findings corroborate recent evidence from observational and modeling studies that Cu clouds experience much entrainment near the cloud top.