Local Spatial Scales of Tropical Deep Convection Inferred from SMM/I Precipitation Data

The local time and space scales of organized tropical deep convection have been studied by L. Ricciardulli and P. D. Sardeshmukh (2002, J. Climate, 15, 2775; hereafter RS) using Global Cloud Imagery. The SSM/I data from the DMSP satellites provides a complimentary data set for this purpose with the advantage of well-tested algorithms for converting brightness temperatures into precipitation. The disadvantage is that the sampling interval of 12 hours is too long to study the short time scales. Taking several months of data using the precipitation algorithm of Ferriday and Avery, convectively active months were defined as those having greater than 2 mm/hr of rain greater than 5% of the time. A plot of the probability of precipitation in the +/-30 degree latitude window will be shown estimated as the percentage of the total 12-hourly average precipitation values using a 40 x 40 km grid having greater than 2 mm/hr. Finally, spatial autocorrelations were preformed on the grid cells for convectively active months and a plot of the spatial scale distribution derived from the autocorrelations was made following RS. These results will be compared with those of RS and will be used as a basis to extend the study to complete global coverage.