Tropical Precipitation Rates during SOP-1, FGGE, Estimated from Heat and Moisture Budgets

Abstract

This study presents global estimates of precipitation rates from 30°N to 30°S, derived from the ?apparent? heat source (Q1) and ?apparent? moisture sink (Q2) budgets using the NASA Goddard Laboratory for Atmospheres Level III-b analyses collected during the first special observing period (SOP-1) of the Global Weather Experiment. In each technique precipitation is solved as the residual. Because of the assumptions made, the techniques yield the most reliable results in the summer hemisphere. Therefore, area averages of precipitation rates are presented to examine the variability of rainfall among selected regions in the Southern Hemisphere tropics. These regions include Africa, the Indian Ocean, the Australian monsoon, the South Pacific convergence zone (SPCZ), and the South American/South Atlantic convergence zone (SACZ). Time averages of precipitation rates are also calculated for two periods (10?24 January and 28 January?11 February 1979) that were selected because of significant changes observed in the convective activity. In the first period intense convection was indicated in the SPCZ, with a subsequent lack of activity there in the latter period. During the second period, a buildup of convective activity was noted in the Indian Ocean. Vertical profiles of heating are also presented for each region and comparisons are made between the profile for the SPCZ and convectively active regions investigated elsewhere in previous studies. Finally, precipitable water (W) is computed and compared to results derived from satellite microwave measurements, as well as to the budget-produced precipitation patterns. Results indicate that the heat and moisture budget estimates of precipitation compare favorably. The vertical advection term in both techniques is found to be the dominant contributor to Q1 and Q2. Vertical profiles reveal that maximum convective heating occurs in the middle troposphere and the profile of the SPCZ region compares best with those over the western North Pacific. In general, the largest values of W are observed in the area of lowest outgoing longwave radiation and strongest rainfall rates. Patterns of W from GLA compared well with those from the satellite measurements.