An Application of a Geostationary Satellite Rain Estimation Technique to an Extratropical Area

The use of geostationary satellite data for estimating precipitation in non-tropical areas was explored with data taken in Montreal, Canada. The previous studies using geostationary images for rain estimation have concentrated primarily on tropical clouds (Griffith et al., 1978; Stout, et al., 1979). The intent of this study was to evaluate the applicability of using these data and techniques in other geographical areas. The Montreal area provided a wide range of weather situations common to midlatitudes for which the techniques could be tested. Because of the many variables in this area (different cloud types, moisture availability, temperature vertical structure and others) the rain rates of the cloud areas varied. Large differences in rain rates between the days studies in Montreal were found. The Montreal data also had rain rates that were considerably smaller than found in the tropical studies. To explain these differences the environments of the clouds were investigated using sounding data. By applying a cumulus model (Simpson and Wiggert, 1969) to the soundings most of the daily differences in rain rates were explained. The large differences between the tropical studies and Montreal also were described by the model. It is proposed that future rain estimation schemes combine satellite image with sounding data through a cloud model to form a technique applicable to a wide variety of weather situations and geographical areas.