Moisture Budget Analysis of TOGA COARE Area Using SSM/I-Retrieved Latent Heating and Large-ScaleQ₂Estimates

This study addresses the retrieval of tropical open-ocean latent heating using Special Sensor Microwave Imager (SSM/I) satellite measurements. The analysis is carried out for the Tropical Ocean and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) intensive observation period in the western Pacific, much of it focused on the study area of the third WCRP–GPCP Algorithm Intercomparison Project (AIP-3) situated over the TOGA COARE Inner Flux Array (IFA). The retrieval algorithm is a profile-type physical inversion scheme based on the use of multispectral passive microwave (PMW) measurements. It estimates vertically distributed rain rate and latent heating by first retrieving mixing ratio profiles of liquid and frozen hydrometeors and then calculating rain fallout rates and vertical derivatives of the liquid–ice mass fluxes. Various modifications to the existing algorithm are discussed, including a combined visible–infrared–PMW–radar screening scheme for distinguishing among "clear," "cloud without rain," and "cloud with rain pixels" to better delineate vertical heating structure. Validation of retrieved rain rates over the AIP-3 study area indicates acceptable accuracy/precision uncertainty levels in terms of intensity, distribution, and time variation. A procedure is developed for improving the initially retrieved heating profiles based on calibration to shipboard radar measurements. The modified algorithm and calibration scheme were applied to the IFA for estimating vertical profiles of latent heating. An optimum high-quality sounding period (1–17 February 1993) was selected for large-scale diagnostic calculations of apparent heating (Q1) and moistening (Q2) to analyze heat-moisture budgets of convective and stratiform cloud systems. Comparison and sensitivity tests indicate that the retrieved latent heating and Q1/Q2 calculations are representative. Moisture budget analyses over the IFA were carried out to study the detailed heating structures of clouds, particularly the cumulus scale heating process. This was accomplished by using residuals between the SSM/I-retrieved latent heating and the large scale Q2 diagnostics. Results show that estimates of daily eddy vertical moisture flux divergence contain sizable uncertainties, however, by averaging over extended periods and vertically integrating to obtain surface latent heat flux transfer, close agreement to independently derived surface evaporation rates is found. This suggests that by combining the SSM/I retrievals with large-scale sounding data, it is possible to shed light on the role of cumulus convection on diabatic heating.