Assessing the Oceanic Water Cycle with an Integrative Approach

虽然许多项目都声称要研究全球水循环，但没有一个项目能恰当地解决其中最大的组成部分--海洋。海洋是迄今为止地球上最大的水库，是大多数蒸发的来源和大多数降水的汇。过去40年来海洋盐度的趋势表明全球水循环正在发生变化。然而，由于缺乏数据，对广阔海洋区域的水循环进行定量评估仍然具有挑战性。在这项研究中，需要支持利用新的海洋通量气候学数据、河流流量数据、不断扩大的海洋盐度监测网络和同化全球海洋环流模式，以审查全球海洋水循环的平均状态、季节循环、趋势和变异性。一般认为，全球变暖将加强水循环，因为更温暖的空气具有更大的蒸汽携带能力。水的蒸气压在全球平均温度14 ℃时约为15 mb，在此温度下增加约1 mb/oC。因此，假设风的输送没有显著变化，1 ℃的温度上升可能会使水循环增加约7%。这是大约10厘米/年的蒸发减去降水（E-P）的差异为1.5米/年。这是从过去40年亚热带大西洋的盐度趋势推断出的蒸发量增加。建议的综合方法结合新的通量数据和数据同化海洋环流模式，以解决以下四个一般性问题的海洋水循环：（1）什么是大气，海洋和陆地之间的净水交换的平均和季节模式？对海洋而言，淡水的纬向通量和流域间输送意味着什么？(2)河水排放与降雨对上层海洋温盐结构的影响是什么？蒸发或降水强迫造成上层海洋混合的哪些变化，上层海洋混合如何影响海洋吸收、储存、运输和释放热量和淡水的能力？由地表通量变化引起的盐度异常的路径和时间尺度是什么？这些对气候有何影响？(3)陆地和海洋淡水储存的季节性和年际变化是什么，这些变化如何影响海洋上层的盐度分布？蒸发量和降雨量的变化是由于风型、SST或大气湿度的变化吗？(4)海洋的哪些区域对淡水强迫的反应最敏感和最有趣？在即将进行的Aquarius盐度卫星使命（2009年发射）期间，哪些区域最适合进行海洋/大气过程研究？更广泛的影响：提高我们对水循环的认识将对社会大有裨益，因为预测供水趋势是规划水资源分配的基础。海洋是理解这一点的关键;大西洋降雨量仅增加百分之一，就会使密西西比河的流量增加一倍。该项目将发展海洋学家、地表通量专家和模型制作者之间的联系，以研究全球海洋淡水的海洋-大气-陆地交换。获得的任何知识都将提高我们对水循环及其对海洋吸收，储存和运输热量能力的影响的理解。因此，将能够更好地了解气候系统的这一关键组成部分，从而增加预测未来变化的机会。最后，将支持在这一重要领域培训一名研究生，并将建立一个关于海洋水循环的网站，帮助确定可能进行盐度限制的海洋-大气交换过程研究的地点。

ABSTRACTOCE-0647949Though many programs purport to study the global water cycle, none have properly addressed its largest component, the oceans. The oceans are by far the largest reservoir of water on Earth, the source of most evaporation and the sink of most precipitation. Trends in ocean salinities over the past 40 years provide indications of a changing global water cycle. However, quantitative assessment of the water cycle over the vast oceanic areas remains challenging because of the scarcity of data. In this study, a support is requested to utilize data from new ocean flux climatologies, river flow data, growing oceanic salinity monitoring networks and an assimilative global ocean circulation model to examine the mean state, seasonal cycle, trends and variability in the water cycle over the global ocean.Intellectual impact: It is generally assumed that global warming will enhance the water cycle, due to the greater vapor carrying capacity of warmer air. The vapor pressure of water is about 15mb at the mean global temperature of 14oC and increases about 1mb/oC at this temperature. Thus, a 1oC temperature rise may enhance the water cycle by ~ 7%, assuming transport by the wind is not changed dramatically. This is about 10cm/year for an evaporation minus precipitation (E-P) difference of 1.5m/yr. This is the sort of evaporation increase inferred from salinity trends in the subtropical Atlantic over the past 40 years. The suggested integrative approach combines new flux data and a data assimilating ocean circulation model to address the following four general issues regarding the oceanic water cycle:(1) What are the mean and seasonal patterns of net water exchange between atmosphere, ocean and land? What meridional fluxes and inter-basin transports of freshwater are implied for the oceans? (2) What are the consequences of river water discharges vs. rainfall for upper ocean thermohaline structure? What changes in upper-ocean mixing result from evaporative or precipitative forcing and how does upper ocean mixing affect the oceans ability to absorb, store, transport and release heat and freshwater? What pathways and timescales are found for salinity anomalies generated by surface flux changes? How do these feedback on climate?(3) What are the seasonal and interannual variations in the land and ocean storage of freshwater and how do these affect the upper-ocean salinity distribution? Are changes in evaporation and rainfall due to variations in winds patterns, SST, or atmospheric humidity?(4) Which regions of the ocean show the most sensitive and interesting response to freshwater forcing? Which regions would be best for an ocean/atmosphere process study during the upcoming Aquarius salinity satellite mission (2009 launch)?Broader impacts: Advancing our understanding of the water cycle will be of great benefit to society, as anticipation of trends in water supplies is fundamental for planning allocation of water resources. The ocean is key to this understanding; the addition of only one percent of Atlantic rainfall would double the discharge of the Mississippi river. This project will develop ties between oceanographers, surface flux experts and modelers to study the ocean-atmosphere-land exchanges of freshwater for the global ocean. Any knowledge gained will improve our understanding of the water cycle, and its effects on the ability of the ocean to absorb, store and transport heat. Thus, an improved understanding of this key component of the climate system will be achieved, thereby leading to greater chances of predicting future changes. Finally, the training of one graduate student in this important area will be supported, and a web site on the oceanic water cycle and help identify likely sites for salinity constrained ocean-atmosphere exchange process studies will be developed.This Project is a contribution to the U.S. CLIVAR (CLImate VARiability and predictability) Program.