Assimilation of GOES-derived solar insolation into a mesoscale model for studies of cloud shading effects

摘要

Cloud cover is capable of generating mesoscale temperature gradients by shading the surface. The purposes of this paper are to utilize GOES visible imagery to assimilate cloud shading elTects into a mesoscale model and to examine the ability of a realistic treatment of moving and changing cloud fields to produce boundary layer convergence zones which may lead to preferred areas of deep convective development. A simplified version of the radiative model of Gautier et Ill. is used to convert hourly gridded GOES brightness data into surface insolation for assimilation into the mesoscale model. The conversion process is presented in detail so that readers may duplicate the assimilation scheme. A case in the Texas Panhandle on 24 and 25 April 1982 is studied. Results of the modelling study show that cloud shading produces (a) a much more complicated surface temperature field, (b) a large change in the planetary boundary layer depth, and (c) substantial boundary layer convergence zones compared to a simulation without cloud shading. These mesoscale effects, in association with synoptic-scale instability, may be important in thunderstorm and severe weather development. The techniques utilized for assimilating satellite-derived insolation may be especially important in after-the-fact mesoscale modelling of air pollution cases and in field studies.