Influence of the Background Wind on the Local Soil Moisture-Precipitation Feedback
Influence of the Background Wind on the Local Soil Moisture-Precipitation Feedback
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DOI：
10.1175/jas-d-13-0180.1
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发表时间：
2014-02-01
影响因子：
3.1
通讯作者：
Schaer, Christoph
中科院分区：
文献类型：
--
作者：
Froidevaux, Paul;Schlemmer, Linda;Schaer, Christoph
土壤湿度异常对半干旱地区气团对流的重要性已经在一些研究中被认识到。潜在的机制在一定程度上仍不清楚。一个悬而未决的问题是，为什么更潮湿的土壤会导致降雨量的增加或减少(分别是土壤水分-降水的正反馈或负反馈)。在这里，一个理想化的云分辨模式框架被用来探索当地土壤水分-降水反馈。这种方法能够根据环境参数复制正反馈和负反馈循环，其机制依赖于水平土壤水分变化，这种变化可能会自发发展和增强。反馈的积极表达与干土块上对流的启动有关，但对流单体随后在潮湿的块上传播，在那里它们加强并优先沉淀。当风廓线太弱，不能支持对流特征从干燥地区传播到潮湿地区时，可能会出现负反馈。然后，降水一般较弱，优先于干燥的地区。这些结果突出了对流层中层气流在决定反馈符号方面的作用。正反馈的一个关键因素是利用干燥斑块上的低对流抑制(CIN)(用于启动对流)和湿斑块上的高CAPE(用于产生降水)。
The importance of soil moisture anomalies on airmass convection over semiarid regions has been recognized in several studies. The underlying mechanisms remain partly unclear. An open question is why wetter soils can result in either an increase or a decrease of precipitation (positive or negative soil moisture-precipitation feedback, respectively). Here an idealized cloud-resolving modeling framework is used to explore the local soil moisture-precipitation feedback. The approach is able to replicate both positive and negative feedback loops, depending on the environmental parameters.The mechanism relies on horizontal soil moisture variations, which may develop and intensify spontaneously. The positive expression of the feedback is associated with the initiation of convection over dry soil patches, but the convective cells then propagate over wet patches where they strengthen and preferentially precipitate. The negative feedback may occur when the wind profile is too weak to support the propagation of convective features from dry to wet areas. Precipitation is then generally weaker and falls preferentially over dry patches. The results highlight the role of the midtropospheric flow in determining the sign of the feedback. A key element of the positive feedback is the exploitation of both low convective inhibition (CIN) over dry patches (for the initiation of convection) and high CAPE over wet patches (for the generation of precipitation).