Enhanced daytime occurrence of clouds in the tropical upper troposphere over land and ocean

Day-night changes in the altitudinal distribution of tropical clouds are examined using multi-year analyses of CloudSat and CALIPSO data. The combined occurrence of all cloud types maximizes in the nighttime throughout the middle and upper troposphere. In contrast to the nighttime maxima in the appearance of optically thick tropical clouds in the ~ 5-12 km altitude band, the occurrence of such clouds exhibit a pronounced daytime enhancement in the upper troposphere (> 12 km). This arises from the more frequent occurrence of thick cirrus and deeper penetration of daytime convective clouds to the upper troposphere, as evidenced from more frequent daytime occurrence of clouds with thickness > 9 km. Apart from the afternoon convection over land and remnant cirrus from nighttime convection over ocean, the daytime cloud enhancement observed above 12 km altitude might be also driven by the larger tropospheric net cloud radiative heating and its vertical gradient during the daytime.