Coincident measurements from TMI and PR are complementary: passive microwave radiometers measure radiances that are the end product of the integrated effects of electromagnetic absorption–emission and scattering through the precipitating cloud along the sensor viewpath. The combination of satellite-borne passive and active sensors to be deployed in the upcoming TRMM promises to provide critical information regarding the three-dimensional distributions of precipitation and heating in the Tropics ( Simpson et al. It was scheduled to be launched in the summer of 1997 with a mission life of at least 3 years. The space segment of TRMM is a satellite in a 350-km circular orbit with a 35° inclination angle. Additionally, the TRMM satellite will carry two related Earth Observing System (EOS) instruments in the Clouds and Earth’s Radiant Energy System (CERES) and the Lightning Imaging System (LIS). The primary rainfall instruments on TRMM are the TRMM Microwave Imager (TMI), the precipitation radar (PR), and the Visible and Infrared Radiometer System (VIRS). The objectives of TRMM are to measure rainfall and energy (i.e., latent heat of condensation) exchange of tropical and subtropical regions of the world. The Tropical Rainfall Measuring Mission (TRMM) is a joint mission between the National Aeronautics and Space Administration (NASA) of the United States and the National Space Development Agency (NASDA) of Japan. Since the Tropics are 75% covered with ocean, precipitation over the global Tropics can be measured satisfactorily only from space. This gap in the center of the hydrologic cycle has had negative impacts on nearly all earth sciences and their applications. Scarcity of quantitative precipitation information has been a frustrating long-time bottleneck for atmospheric science. The poor simulation of cloud properties is one of the factors causing the models to differ so widely regarding the amount of global warming with doubled carbon dioxide. All of these models inadequately predict precipitation and soil moisture. Presently, there are large discrepancies among the results of the different models. In the Tropics particularly, it is vitally important to have rain and its latent heating in the initialization of global weather and climate models, as well as in their prediction stage. Most of these parameterizations are extremely crude.
However, global models for prediction of weather and climate have much coarser resolution, therefore they must “parameterize” cloud processes.
These differences are due to both the lack of good direct measurements of rainfall, as well as the highly variable nature of the parameters both spatially and temporally.Ĭloud and rain processes are now simulated fairly well on the scale of cloud ensembles (50–100 km). Quantitative estimates of tropical precipitation, unfortunately, still vary by as much as 100%, depending upon the estimates. Instead, several seasons of drought and starvation are often followed by a year or two of torrential downpours and disastrous floods. The “average” rainfall is rarely observed. The most important impact of rain and its variability is on the biosphere, including humans. Differences in large-scale rainfall patterns and their associated energy release in the Tropics, in turn, affect the entire global circulation, as manifested in El Niño events, to name just one example. The atmosphere gets three-fourths of its heat energy from the release of latent heat by precipitation, and an estimated two-thirds of this precipitation falls in the Tropics.
0 kommentar(er)
