The Relationship between Fractional Coverage of High Cloud and Rainfall Accumulations during GATE over the B-Scale Array

Abstract

A description is given of the relationship between 6 h averages of fractional coverage of cloud above various height and temperature thresholds, derived from infrared data from the Synchronous Meteorological Satellite 1 (SMS 1), and accumulated rainfall, derived from data obtained with a group of quantitative C-band digital radars. Comparisons are made over a hexagonal area extending from 22.25?24.75°W longitude and from 7?10°N latitude (the B-scale array) for each phase of the GARP Atlantic Tropical Experiment (GATE). Scattergrams of fractional coverage above 10 km, the altitude of maximum correlation, show a linear relationship for each phase, with correlations ranging from 0.81 to 0.89. Reanalysis of Phase I, omitting a single outlier, results in a very narrow range for the regression coefficients for all three phases. An analysis of the pooled data from all three phases, omitting the single outlier, shows that 75% of the variance in 6 h rainfall accumulations over the GATE B-scale array is explained by a linear function of the fraction of the array covered by cloud higher than 10 km.