Observations of shallow trade-wind cumulus cloudiness and mass flux variability and their relationship to boundary layer structure

Oceanic cumuli are ubiquitous in the subtropics and help regulate the thermodynamic structure of the lower troposphere and the large-scale tropical circulation. Yet, observations of the vertical structure of marine cumulus cloudiness and mass flux remain sparse. Fortunately, modern island-based remote sensors more specifically, the Barbados zenith cloud radar posses the sensitivity to study hydrometers which, when small enough, can also be used as tracers of air motion.Over the 2-years analyzed, the daily cloud fraction profile of cumulus non-precipitating (peak 4.5 % at 710 m), precipitating without (peak 2.3 % at 809 m) and with attached stratiform layers (peak 1 % at 1679 m) oscillate slightly (~ 3 %). Precipitating cumuli with stratiform outflows are deeper and contain more abrupt vertical variations in reflectivity and Doppler velocity than other precipitating cumuli. Non-precipitating cumuli exhibit an elevated reflectivity core and an ascendant center surrounded by a subsiding shell. Bulk (3 h) statistics reveal that these cloud are active and organized. They contain 79 % updrafts with 86 % of them being organized in large coherent structures contributing to a maximum updraft mass flux of 0.008- 0.036 kgm-2s-1 just above cloud base. Alternatively, downdrafts contribute insignificant mass flux and show little vertical and temporal variability (0.000-0.007 kgm-2s-1). Together with complementary Raman lidar information, normalized updraft mass flux profiles suggest that updraft mass flux profile slope is inversely related to environmental relative humidity. Similarly, the presence of stratiform detrained layers coincides with moistening under the inversion layer. Altogether, the analysis presented here is useful for evaluating and constraining the representation of cloudiness and mass flux schemes in numerical models. %%%%Les cumulus oceaniques sont omnipresents dans les regions subtropicales et aident a reguler la structure thermodynamique de la basse troposphere ainsi que la circulation tropicale a grande. Pourtant, une penurie d'observations de la distribution verticale des cumulus oceaniques et de leur flux de persiste. Par chance, les capteurs a distance modernes bases sur des iles, plus precisement le radar de nuage vertical de la Barbade possede la sensibilite pour etudier les hydrometeores qui, quand ils sont assez petits, peuvent aussi etre utilises pour retracer le mouvement de l'air.Au cours des 2 ans analyses, le profile de fraction nuageuse des cumulus sans precipitation (maximum 4.5 % a 710 m), avec precipitation sans (maximum 2.3 % a 809 m) et avec segments stratiformes attaches (maximum 1 % a 1679 m) oscille legerement (~ 3 %). Les cumulus avec precipitation et couche stratiforme detrainee sont plus epais et contiennent des variations de reflectivite et de vitesse Doppler plus abruptes que les autres cumulus pluvieux. Les cumulus sans precipitation possedent un noyau de reflectivite sureleve et un centre ascendant entoure par une coquille descendante. Des statistiques globale (3 h) montrent que ces…