Assessing the Oceanic Water Cycle with an Integrative Approach

尽管许多项目都声称要研究全球水循环，但没有一个项目恰当地研究了其最大的组成部分——海洋。海洋是迄今为止地球上最大的水库，是大部分蒸发的来源和大部分降水的汇。过去40年海洋盐度的趋势提供了全球水循环变化的迹象。然而，由于缺乏数据，对广大海洋地区的水循环进行定量评估仍然具有挑战性。在本研究中，要求支持利用来自新的海洋通量气候学、河流流量数据、不断增长的海洋盐度监测网络和同化的全球海洋环流模式的数据来检查全球海洋水循环的平均状态、季节周期、趋势和变异。智力上的影响：一般认为全球变暖将加强水循环，因为较暖的空气携带水汽的能力更大。在全球平均温度为14oC时，水的蒸汽压约为15mb，在此温度下，水的蒸汽压增加约1mb/oC。因此，假设风的输送没有发生显著变化，温度升高1℃可能使水循环增加约7%。对于1.5米/年的蒸发-降水（E-P）差，这大约是10厘米/年。这是根据过去40年亚热带大西洋的盐度趋势推断出的那种蒸发增加。建议的综合方法结合了新的通量数据和数据同化的海洋环流模式，以解决关于海洋水循环的以下四个一般性问题：(1)大气、海洋和陆地之间净水交换的平均和季节模式是什么？海洋的经向通量和盆地间淡水输送隐含了什么？(2)河流排水与降雨对上层海洋热盐结构的影响是什么？蒸发或降水强迫导致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？地表通量变化引起的盐度异常有哪些途径和时间尺度？这些对气候有什么影响？(3)陆地和海洋淡水储量的季节和年际变化是什么？这些变化如何影响上层海洋的盐度分布？蒸发和降雨的变化是由于风型、海温或大气湿度的变化吗？(4)海洋的哪些区域对淡水强迫表现出最敏感和有趣的响应？在即将到来的水瓶座盐度卫星任务（2009年发射）中，哪个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理解将对社会大有裨益，因为对供水趋势的预测是规划水资源分配的基础。海洋是这种理解的关键；只要大西洋降雨量增加1%，密西西比河的流量就会增加一倍。该项目将发展海洋学家、地表通量专家和建模者之间的联系，以研究全球海洋淡水的海洋-大气-陆地交换。所获得的任何知识都将提高我们对水循环的理解，以及它对海洋吸收、储存和运输热量的能力的影响。因此，将增进对气候系统这一关键组成部分的了解，从而更有可能预测未来的变化。最后，将支助在这一重要领域培训一名研究生，并将编制一个关于海洋水循环的网站，并帮助确定受盐度限制的海洋-大气交换过程研究的可能地点。该项目是对美国CLIVAR（气候变率和可预测性）计划的贡献。

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.