Impact of Scatterometer Winds on Hydrologic Forcing and Convective Heating through Surface Divergence

Abstract

One of the difficulties in estimating atmospheric heat and moisture budgets lies in resolving the near-surface heat and moisture convergence and vertical velocities, each of which is highly dependent on the divergence of the surface wind. A kinematic approach is proposed to utilize scatterometer winds to improve the estimate of surface wind divergence, the omega profile, and, therefore, estimates of the hydrologic forcing and convective heating over the tropical ocean. Improvements in these estimates over those obtained using analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF) alone are found when the ERS-1 scatterometer ground tracks passed over the TOGA COARE intensive flux array. The spatial patterns of precipitation estimated from GMS IR temperatures and radar reflectivities agree better with the divergence fields derived from the ERS-1 scatterometer winds than with those derived from either ECMWF or rawinsonde winds. The use of ERS-1 surface winds also changes the omega profiles throughout the atmosphere. The heat and moisture budgets are sensitive to vertical velocity and are, therefore, significantly affected by the inclusion of scatterometer winds. Precipitation estimates from GMS IR temperatures are found to agree better with those estimated from budget residuals computed using scatterometer winds.