On the annual cycle in highest, coldest clouds in the tropics

High-resolution satellite observations are used to examine the annual cycle in mean areal coverage by highest, coldest clouds in the tropics. It is found that the mean fractional coverage by clouds with cloud-top temperatures below 200 K undergoes an annual cycle in phase with the annual cycle in tropopause height and temperature. The maximum mean fractional coverage by these clouds tends to occur during the northern winter when the tropopause is the highest and coldest throughout the tropics. The annual cycle in lower and warmer cirroform clouds is much less significant. This relationship is observed for various subregions of the tropics as well as for the tropics as a whole. -Author