Estimates of Radiative Divergence during Phase III of the GARP Atlantic Tropical Experiment Part I. Methodology

Abstract

The methodology used to generate the GATE A/B-scale radiative divergence budget estimates is described. The technique consists of compositing radiative divergence profiles on the basis of synoptic observations and satellite and radar inferred cloud structure. Cloud-top distributions were generated from SMS infrared brightness data observed hourly over the entire GATE A/B array. Cloud-clear thresholds were determined using concurrent visible brightness and infrared brightness observations. Corrections to cloud-top height were made for water vapor extinction and for non-blackness of clouds. Cloud-base distributions were inferred statistically from a limited sample of concurrent radar and satellite data. Temperature and moisture distributions from 6 h synoptic analyses of rawinsonde data were used in the radiative divergence computations. The computational algorithms used to generate the shortwave and longwave radiation divergence estimates were compared with aircraft observations; average cloud properties of upper level clouds inferred from the observations were used in the computational algorithms. The area-average radiative divergence profiles were then generated by computational algorithms.