CLIMATIC-SCALE VEGETATION - CLOUD INTERACTIONS DURING DROUGHT USING SATELLITE DATA

Land-surface-atmosphere interactions for the 1988 summer drought in th e Mid-west USA are studied at climatic scales (10(4) km2; > 5 days) us ing polar orbiter satellite radiance information on vegetation activit y and cloud conditions. The emphasis is on documenting the occurrences of 'organized' land-cover types and cumulus convection, and evaluatin g their mutual associations. For purpose of comparison, similar analys es are performed for the more moisture sufficient (non-drought) summer of 1987. The satellite retrievals and analysis methods are calibrated using station meteorological data on precipitation and surface moistu re, and also land-cover maps. In early summer (June) 1988, Mid-west US A land surfaces were generally highly stressed (high shortwave reflect ance, high surface temperatures), particularly for the Corn Belt. More over, the spatial variation of the land-cover signal was greater than in June 1987, and also when compared with later that summer (August 19 88). Statistical analysis suggests a significant role for the land sur face conditions of early summer in the spatial patterns of deep convec tion over the remainder of the season. This involves generally higher (lower) frequencies of convective cloud days for surfaces having a hig h relative density of forest vegetation (crops). Because broadly simil ar results are obtained for the summer of 1987, the possibility exists that the vegetation-convective-cloud interaction may be a feature of Mid-west USA summer climate. The diurnal dependence of cloud-forming p rocesses for agricultural and natural vegetation regions is assessed u sing GOES cloud imagery at high temporal resolution for a 'typical' co nvective day in early summer 1988. Associations with station radiosond e data support the hypothesis that spatial differences in land cover i nfluence the generation and timing of convective cloudiness for the Mi d-west region.