The Diurnal March of Convective Cloudiness over the Americas

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Abstract
Based on nine years (1983–91) of infrared data from geostationary satellites (the B3 ISCCP product), several features of the diurnal march of the frequency of convective cloudiness over the tropical and subtropical Americas are documented with 3-h temporal resolution and 0.5° × 0.5° latitude–longitude spatial resolution. The frequency of convective cloudiness in each grid box is defined in terms of the fraction of temporal samples that exhibit cloud-top temperatures colder than 235 K. The effect of varying the threshold is explored and selected results are compared with rainfall estimates based on microwave (SSM/I) imagery. Convective cloudiness over most land areas exhibits a coherent diurnal march with relatively clear mornings, a rapid afternoon buildup, and a more gradual nighttime decay. The highest, coldest convective clouds peak a few hours earlier than those with lower tops. Morning to noontime maxima tend to be prevalent over offshore waters that experience significant convection such as... Abstract Based on nine years (1983–91) of infrared data from geostationary satellites (the B3 ISCCP product), several features of the diurnal march of the frequency of convective cloudiness over the tropical and subtropical Americas are documented with 3-h temporal resolution and 0.5° × 0.5° latitude–longitude spatial resolution. The frequency of convective cloudiness in each grid box is defined in terms of the fraction of temporal samples that exhibit cloud-top temperatures colder than 235 K. The effect of varying the threshold is explored and selected results are compared with rainfall estimates based on microwave (SSM/I) imagery. Convective cloudiness over most land areas exhibits a coherent diurnal march with relatively clear mornings, a rapid afternoon buildup, and a more gradual nighttime decay. The highest, coldest convective clouds peak a few hours earlier than those with lower tops. Morning to noontime maxima tend to be prevalent over offshore waters that experience significant convection such as...

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