Understanding Decreases in Land Relative Humidity with Global Warming: Conceptual Model and GCM Simulations
Understanding Decreases in Land Relative Humidity with Global Warming: Conceptual Model and GCM Simulations
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DOI：
10.1175/jcli-d-16-0351.1
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发表时间：
2016-12-01
影响因子：
4.9
通讯作者：
O'Gorman, Paul A.
中科院分区：
文献类型：
--
作者：
Byrne, Michael P.;O'Gorman, Paul A.
气候模式模拟了近地表相对湿度对全球变暖的反应中强烈的陆地-海洋对比;海洋上的相对湿度往往略有增加，但陆地上的相对湿度则大幅下降。表面能量平衡参数已用于理解海洋上的响应，但很难应用于更复杂的陆地表面。在这里，一个概念箱模式，涉及大气水分输送之间的陆地和海洋和地面蒸散，调查在陆地相对湿度随着气候变暖的减少。箱模型应用于理想化和全复杂性（CMIP 5）大气环流模型的模拟，发现它可以捕捉到模拟的陆地湿度变化的许多特征。最简单的盒子模型给出了陆地和海洋上比湿度的相等分数增加。这种关系意味着陆地相对湿度的下降，因为陆地的变暖幅度大于海洋，海洋相对湿度的变化幅度不大，这与以前提出的机制一致。当包括蒸散，它被认为是次要的海洋水分输送相比，在陆地比湿度的增加，但它在陆地相对湿度的下降起着重要的作用。对于在陆地上的水分强迫的情况下，如从气孔关闭，土地相对湿度的响应被强烈放大的引起的陆地表面空气温度的变化，这种放大是量化的使用理论的土地和海洋温度之间的联系。
Climate models simulate a strong land-ocean contrast in the response of near-surface relative humidity to global warming; relative humidity tends to increase slightly over oceans but decrease substantially over land. Surface energy balance arguments have been used to understand the response over ocean but are difficult to apply over more complex land surfaces. Here, a conceptual box model is introduced, involving atmospheric moisture transport between the land and ocean and surface evapotranspiration, to investigate the decreases in land relative humidity as the climate warms. The box model is applied to simulations with idealized and full-complexity (CMIP5) general circulation models, and it is found to capture many of the features of the simulated changes in land humidity. The simplest version of the box model gives equal fractional increases in specific humidity over land and ocean. This relationship implies a decrease in land relative humidity given the greater warming over land than ocean and modest changes in ocean relative humidity, consistent with a mechanism proposed previously. When evapotranspiration is included, it is found to be of secondary importance compared to ocean moisture transport for the increase in land specific humidity, but it plays an important role for the decrease in land relative humidity. For the case of a moisture forcing over land, such as from stomatal closure, the response of land relative humidity is strongly amplified by the induced change in land surface-air temperature, and this amplification is quantified using a theory for the link between land and ocean temperatures.