A mechanism for land-ocean contrasts in global monsoon trends in a warming climate
A mechanism for land-ocean contrasts in global monsoon trends in a warming climate
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DOI：
10.1007/s00382-011-1270-3
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发表时间：
2012-09-01
期刊：
影响因子：
4.6
通讯作者：
Fasullo, J.
中科院分区：
文献类型：
--
作者：
Fasullo, J.
全球季风记录的一个核心矛盾是，在全球水文循环预计和观察都将加强的时代，陆地降雨量报告减少。正是在这种情况下，这项工作开发了物理基础，既解释观测记录和预测气候变暖的季风变化，同时支持全球季风的概念，在共享反馈的背景下。全球陆地季风记录在多个再分析的第一次评估。在其他研究中被认为是真实的趋势，由于在卫星时代之前和期间同化数据流的变化，很可能是虚假的。尽管如此，根据卫星估计，海洋上的季风降雨确实存在强劲增长，这种陆地-海洋对比仍然缺乏物理基础。为了解决对比的原因，因此评估了模拟趋势。虽然总降雨量的预测是不一致的模型，在观测中确定的强大的陆地-海洋对比得到证实。一个反馈机制，提出植根于这样一个事实，即土地面积温暖不成比例地相对于海洋，和陆上流是季风水分的主要来源。因此，陆地上空对流层相对湿度降低是不可避免的，这对季风对流环境有直接影响，包括提升凝结水平的增加和对流分布的转变，通常朝向频率较低和可能更强烈的事件。该机制被解释为对“富-更富”机制的重要调节影响。区域季风的警告存在，并进行了讨论。
A central paradox of the global monsoon record involves reported decreases in rainfall over land during an era in which the global hydrologic cycle is both expected and observed to intensify. It is within this context that this work develops a physical basis for both interpreting the observed record and anticipating changes in the monsoons in a warming climate while bolstering the concept of the global monsoon in the context of shared feedbacks. The global-land monsoon record across multiple reanalyses is first assessed. Trends that in other studies have been taken as real are shown to likely be spurious as a result of changes in the assimilated data streams both prior to and during the satellite era. Nonetheless, based on satellite estimates, robust increases in monsoon rainfall over ocean do exist and a physical basis for this land-ocean contrast remains lacking. To address the contrast's causes, simulated trends are therefore assessed. While projections of total rainfall are inconsistent across models, the robust land-ocean contrast identified in observations is confirmed. A feedback mechanism is proposed rooted in the facts that land areas warm disproportionately relative to ocean, and onshore flow is the chief source of monsoonal moisture. Reductions in lower tropospheric relative humidity over land domains are therefore inevitable and these have direct consequences for the monsoonal convective environment including an increase in the lifting condensation level and a shift in the distribution of convection generally towards less frequent and potentially more intense events. The mechanism is interpreted as an important modulating influence on the "rich-get-richer" mechanism. Caveats for regional monsoons exist and are discussed.