Calibration and validation studies over the North Atlantic and UK for the Global Precipitation Mission

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Understanding the changing global precipitation patterns that result from a changing climate represents one of the great research priorities of the next decades. In order to better define the future we need to understand the present and the inter-annual variability of the precipitation cycle, which mirrors, in short periods, the expected climate-change-induced long-term variability. However, while observational studies based on the past 30 year records suggest rises in precipitation and evaporation at a global rate of 6-7%/K, global and regional climate models predict a muted response of the hydrologic cycle (2-3%/K). Quantitative estimation and prediction of precipitation still remain grand challenges in the hydrological and atmospheric sciences, both carrying huge uncertainties and thus preventing us from solving the previous conundrum. Observation-wise surface precipitation varies on spatial scales ranging from tens of meters to hundreds of kilometers, thus inhibiting the determination of spatio-temporal structures of precipitation fields from pointwise measurements only (e.g. rain gauges). Active and passive space-borne microwave measurements (precipitation radars, multi-wavelength radiometers) are considered to be suitable for estimating day and night-time precipitation rates and distributions on a planetary scale. Thanks to a satellite constellation concept the NASA-JAXA Global Precipitation Mission, due to launch early in 2014, promises to produce a significant step forward in improving coverage and reducing uncertainties in global precipitation products at a level sufficient to critically challenge numerical models. The presence of a first-ever-in-space dual frequency radar in the core satellite, with coverage up to 65 degrees latitude, will allow not only to know how much rain falls at the surface but also the detailed three-dimensional knowledge of rain, snow, and other forms of precipitation within the atmosphere above the surface and, with it, the links and the transfer of latent heat energy between the Earth's surface and atmosphere. This is an unprecedented opportunity in the mid-latitudes.In our effort, by specifically focusing on UK and on the North Atlantic region, we will address two scientific objectives: 1) To quantify, understand, and potentially mitigate regime dependent biases that are present in today's passive microwave rainfall retrieval over ocean; 2) to critically assess the potential of Global Precipitation Mission-era passive microwave rainfall over mid-latitude coastal and rural areas. The UKMO radar network will be used as ground-reference for the satellite products; as a result, improvements on radar-based rainfall estimates over UK are expected as well. In addition, through improved measurements of precipitation globally, the Global Precipitation Mission will help advancing our understanding of Earth's water and energy cycle, improving forecasting of extreme events that cause natural hazards and disasters, and extending current capabilities in using accurate and timely information of precipitation to directly benefit society. This project will foster and help UK scientists and UK society in taking full advantage of such a unique opportunity.