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A preliminary assessment of the capability of GOES visible and infrared sensors in detecting rainfall in midlatitude cyclones

This study examined the capability of current geostationary satellite sensors in resolving important mesoscale rain areas. The mesoscale precipitation patterns were analyzed with radar and recording rain gage data associated with midlatitude cyclones in New England that had relatively little stratiform cloudiness in the upper trososphere. Radar thresholding techniques were used to determine the spatial and temporal scales of small mesoscale areas (SMSA's), of large mesoscale areas (LMSA's), and major echoes. Radar analyses of the three cases showed that the spatial scale of major echoes, LMSA's, and SMSA's were sufficiently large for detection by GOES sensors. In addition, major echoes and the LMSA's contained within them were found to have lifetimes that are long relative to the time interval of half an hour between GOES images. The duration of some SMSA's and all cells, however, was on the same order as the time interval between successive satellite images. Examination of the visible and infrared satellite imagery revealed that the clouds detected in the infrared imagery in the vicinity of major radar echoes were slightly colder then nearby clouds with little or no precipitation. The visible imagery, however, could not separate raining from non-raining areas. The colder infrared regions were able to separate non-rain areas from broad areas in which most of the rain occurred. Detailed comparisons of hourly recording rain gage observations from within the cold infrared region of the GOES satellite showed, however, that a relatively small percent (2-48%) of the gages located in the area of coldest infrared temperatures actually recorded measurable rain. Detailed analysis of the time change of radar echo area and mass flux estimates compared to the time change of infrared satellite areas showed little correspondence. For the cases examined in this study, GOES sensors were not capable of distinguishing individual mesoscale precipitation areas; and therefore, the GOES sensors do not appear adequate for developing satellite rainfall estimation techniques in midlatitude cyclones or in other large-scale features where cumulonimbus clouds do not account for most of the precipitation. Thesis Supervisor: Dr. Robert W. Burpee Title: Visiting Professor of Meteorology