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Understanding the Earth's climate and how it responds to climate perturbations relies on knowledge of how atmospheric moisture, clouds, latent heating, and the large-scale circulation vary with changing climate conditions. The physical process that links these key climate elements is precipitation. GPM will establish a benchmark for global rainfall, building upon the highly successful joint US/Japan Tropical Rainfall Measuring Mission (TRMM). GPM's global atmospheric monitoring of water and energy will be a key contributor to answering the science research strategy questions: (1) How are global precipitation, evaporation, and the cycling of water changing?
(2) How are variations in local weather, precipitation, and water resources related to global climate variation? (3) How can weather forecast duration and reliability be improved by new space-based observations, data assimilation and modeling? In an era of climatic uncertainty we need to be able to detect, understand and react to early signs that rainfall patterns may be changing in concert with better-understood climate variables. The transient nature of rainfall makes the detection of subtle changes difficult. Rainfall information over ~3 hours time scale is needed to improve weather forecast models, data assimilation models, hydrological models and flash flood forecasts. GPM is will substantially improve upon the temporal and spatial coverage of TRMM and extend the measurement of rainfall globally. Global Precipitation Measurement is a global endeavor that has sparked global interest. It has received overwhelming endorsement from the World Climate Research Programme, the World Meteorological Organization, and the Committee on Earth Observation Satellites.
Japan's National Space Development Agency (NASDA) plans to contribute the radar for and launch of a core satellite. The European Space Agency (ESA) is currently conducting a feasibility study for a European constellation satellite contribution to GPM. India and France have expressed their interest in participating through the Megha-Tropiques project. South Korea is proposing the contribution of a constellation satellite bus in addition to regional ground validation sites. Other nations are also expected to play major a role in GPM. GPM is now in formulation and is one of the highest priority new missions for which NASA's Earth Science Enterprise seeks final approval. GPM launches are targeted to begin in 2009.
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