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

了解气候变化导致的全球降水模式变化是未来几十年的重要研究重点之一。为了更好地确定未来，我们需要了解降水周期的现状和年际变化，这在短期内反映了预期的气候变化引起的长期变化。然而，虽然基于过去30年记录的观测研究表明，全球降水和蒸发量以6-7%/K的速度增加，但全球和区域气候模型预测水文循环的响应较弱（2-3%/K）。降水量的定量估计和预测仍然是水文和大气科学中的重大挑战，两者都具有巨大的不确定性，从而阻止我们解决以前的难题。观测到的地面降水量在几十米到几百公里的空间尺度上变化，因此无法仅从逐点测量（例如雨量计）确定降水场的时空结构。主动和被动的空间微波测量（降水雷达、多波长辐射计）被认为适合于估计白天和夜间的降水率和行星尺度的分布。由于卫星星座概念，定于2014年初发射的美国航天局-日本宇宙航空研究开发机构全球降水使命有望在改善覆盖面和减少全球降水产品的不确定性方面向前迈出重要一步，其水平足以对数值模型提出严峻挑战。核心卫星上首次安装了空间双频雷达，覆盖范围可达纬度65度，不仅可以知道地面福尔斯的降雨量，还可以详细了解地面大气层内雨、雪和其他形式降水的三维情况，地球表面和大气之间的联系和潜热能量的传递。这是中纬度地区前所未有的机遇。在我们的努力中，通过特别关注英国和北大西洋地区，我们将解决两个科学目标：1）量化，理解，并可能减轻目前在海洋被动微波降雨反演中存在的依赖于制度的偏差; 2）严格评估全球降水任务时期被动微波降雨在中纬度沿海和农村地区的潜力。UKMO雷达网络将被用作卫星产品的地面参考;因此，预计也将改进基于雷达的英国降雨量估计。此外，通过改进对全球降水量的测量，全球降水量使命将有助于增进我们对地球水和能量循环的了解，改进对造成自然危害和灾害的极端事件的预测，并扩大目前利用准确和及时的降水量信息的能力，以直接造福社会。该项目将促进和帮助英国科学家和英国社会充分利用这样一个独特的机会。

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.