The Tropical Rainfall Measuring Mission (TRMM) is a joint, three-year Japan- US mission as part of NASA's Mission to Planet Earth. The satellite was successfully launched from Japan on November 27, 1997 (US time). It is equipped with the first spaceborne precipitation radar (PR), the TRMM multichannel passive microwave imager (TMI), a lightning imaging sensor (LIS), a visible and infrared sensor (VIRS), and the Clouds and Earth Radiant Energy System (CERES) for measuring upwelling radiation . Some of the key goals of the mission are (1) to estimate the four-dimensional diabatic heating in the tropical and subtropical atmosphere, (2) understand the role of latent heating in driving tropical and extratropical circulations, (3) obtain monthly area- averaged estimates of rainfall over the data-sparse oceans, and (4) estimate the relative contribution of convective and stratiform precipitation over different regions during different seasons. To successfully meet these goals, an improved understanding of cloud and precipitation processes is of vital importance.
Data from the satellite are currently being used to generate a suite of products for use in the scientific community. An important part of TRMM is validation of these products using data from select sites with ground- based radar and rain gauge networks, as well as field campaigns. Field experiments have already been conducted in Texas and the South China Sea in spring of 1998, and Florida in summer of 1998. There are to be major campaigns in Amazonia from November 1998 - February 1999, and Kwajalein Atoll in the summer of 1999, intended to study precipitation systems in archetypical tropical continent and ocean environments. The goals of the field campaigns will be to evaluate the physical models and error estimates associated with the satellite measurements, and the methods used to infer various geophysical parameters (e.g., rainfall, latent heating, vertical profiles of hydrometeor content and particle size distributions, and wind divergence) from the measurements over different temporal and spatial scales. A brief overview of the scientific objectives will be presented, along with selected early results from the 1998 Texas and Florida programs.