Diurnal Variations of Cloud Cover and Their Relationship to Climatological Conditions

Abstract

The ISCCP-C2 cloud climatology is used to describe the three-dimensional structure of cloud diurnal variations and to investigate their relationship to local climatological conditions. The latter follows from the regression of diurnal components onto climatological state variables. Four important diurnal cloud categories are identified. The diurnal variation of maritime high-cloud fraction C′hi maximizes at 1700 local solar time (LST) and is strongest over maritime convective locations where the mean high-cloud fraction is Chi > 0.1. The diurnal variation of maritime low-cloud fraction maximizes at 0400 LST and is strong over maritime nonconvective locations where Chi < 0.1. Diurnal variations of high-cloud fraction (persistent during the night, minimum at 1100 LST) and low-cloud fraction (1300 LST maximum) are strong over all continental locations in the latitude band 40°S–40°N. In each cloud category, most of the diurnal amplitude and phase at individual locations is explained by the regression... Abstract The ISCCP-C2 cloud climatology is used to describe the three-dimensional structure of cloud diurnal variations and to investigate their relationship to local climatological conditions. The latter follows from the regression of diurnal components onto climatological state variables. Four important diurnal cloud categories are identified. The diurnal variation of maritime high-cloud fraction C′hi maximizes at 1700 local solar time (LST) and is strongest over maritime convective locations where the mean high-cloud fraction is Chi > 0.1. The diurnal variation of maritime low-cloud fraction maximizes at 0400 LST and is strong over maritime nonconvective locations where Chi < 0.1. Diurnal variations of high-cloud fraction (persistent during the night, minimum at 1100 LST) and low-cloud fraction (1300 LST maximum) are strong over all continental locations in the latitude band 40°S–40°N. In each cloud category, most of the diurnal amplitude and phase at individual locations is explained by the regression...