Multiyear CloudSat and CALIPSO Observations of the Dependence of Cloud Vertical Distribution on Sea Surface Temperature and Tropospheric Dynamics

Abstract

tilizing the synergy of the capabilities of CloudSat and Cloud?Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and ~4.5 years of their observations, this paper investigates the dependence of the altitude distribution and thickness of tropical clouds on sea surface temperature (SST). Variations in the altitude distribution of clouds with SST show three distinct regimes: SST < 27.5°C, 27.5° < SST < 29°C, and SST > 29°C. At an SST < 27.5°C, the convection is rather weak, so that most of the clouds are limited to <2-km altitude with peak occurrence at 1?1.5 km. The frequency of occurrence of the low-altitude clouds as well as the prominence of the peak at ~1.5 km consistently decreases for SST > 24°C. Vertical development of clouds through the 3?12-km-altitude region increases for SST > 27.5°C to achieve maximum cloud occurrence and thickness in the SST range of 29°?30.5°C. Penetration of the deep convective clouds to altitudes >15 km and their frequency of occurrence increase with SST until ~30°C. These observations reveal two differences with the SST dependence of total cloudiness observed using passive imager data: (i) the increase in cloudiness at an SST > 26°?27°C observed using the imager data is found to be influenced by the increase in cirrus clouds generated by deep convective outflows and is not directly driven by the local SST, and (ii) the total cloudiness does not decrease for SST > 29.5°C as observed using imagers, but weakly increases until an SST of ~30.5°C. The role of the spatial gradient of SST and atmospheric dynamical parameters in modulating the observed SST dependence of cloudiness at different SST regimes is investigated.