Relative humidity changes in a warmer climate
Relative humidity changes in a warmer climate
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DOI：
10.1029/2009jd012585
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发表时间：
2010-05-07
影响因子：
4.4
通讯作者：
O'Gorman, Paul A.
中科院分区：
文献类型：
--
作者：
Sherwood, Steven C.;Ingram, William;O'Gorman, Paul A.
由于水蒸气和云的关键气候反馈很大程度上取决于相对湿度R在温暖气候中的变化，但这还没有在模型中得到广泛的分析。来自CMIP 3存档的大气环流模型（GCM）和这里研究的几个更高分辨率的大气GCM通常预测R趋势与全球温度的特征模式，这些模式以前在单个模型中报道过，包括对流层顶周围的增加，热带对流层上部的减少和中纬度的减少。这一模式与以前报告的相同大气环流模式中的云量模式非常相似，证实了R在控制模拟云变化方面的作用。比较不同的模式，对流层的每一个部分的趋势近似成正比的向上和/或极向梯度的R在目前的气候。虽然这表明这些变化只是反映了R型随着对流层顶向上移动和随着纬向急流向极地移动，但副热带地区的干燥趋势大约是副热带特征变化的3倍，并且副热带R最小值在大多数模式中加深。R趋势与水平模式分辨率相关，特别是在热带地区以外，它们显示出收敛的迹象，纬度梯度接近T85及更高的GCM分辨率。我们认为，大部分的系统性变化R可以解释当地特定的湿度已设置（冷凝）在偏远地区不同的温度变化，因此梯度和趋势，每个依赖于一个模型的能力，以解决水分输送。最后，仅从变暖预测的亚热带干燥趋势远远低于近几十年来观察到的趋势。虽然这种差异支持以前的报告GCM低估了哈德利细胞的扩张，我们的研究结果意味着，单独的变化是不足够的解释的变化。
Key climate feedback due to water vapor and clouds rest largely on how relative humidity R changes in a warmer climate, yet this has not been extensively analyzed in models. General circulation models (GCMs) from the CMIP3 archive and several higher resolution atmospheric GCMs examined here generally predict a characteristic pattern of R trend with global temperature that has been reported previously in individual models, including increase around the tropopause, decrease in the tropical upper troposphere, and decrease in midlatitudes. This pattern is very similar to that previously reported for cloud cover in the same GCMs, confirming the role of R in controlling changes in simulated cloud. Comparing different models, the trend in each part of the troposphere is approximately proportional to the upward and/or poleward gradient of R in the present climate. While this suggests that the changes simply reflect a shift of the R pattern upward with the tropopause and poleward with the zonal jets, the drying trend in the subtropics is roughly 3 times too large to be attributable to shifts of subtropical features, and the subtropical R minima deepen in most models. R trends are correlated with horizontal model resolution, especially outside the tropics, where they show signs of convergence and latitudinal gradients become close to available observations for GCM resolutions near T85 and higher. We argue that much of the systematic change in R can be explained by the local specific humidity having been set (by condensation) in remote regions with different temperature changes, hence the gradients and trends each depend on a model's ability to resolve moisture transport. Finally, subtropical drying trends predicted from the warming alone fall well short of those observed in recent decades. While this discrepancy supports previous reports of GCMs underestimating Hadley cell expansion, our results imply that shifts alone are not a sufficient interpretation of changes.