The sensitivity of the West African monsoon circulation to intraseasonal soil moisture feedbacks
The sensitivity of the West African monsoon circulation to intraseasonal soil moisture feedbacks
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西非季风环流对季节内土壤湿度反馈的敏感性
DOI：
10.1002/qj.4274
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发表时间：
2022
影响因子：
8.9
通讯作者：
Talib J
中科院分区：
文献类型：
--
作者：
Talib J
季节内土壤湿度变化有可能通过影响地表湍流通量和行星边界层特征而反馈到西非季风环流。利用卫星观测和大气再分析，我们研究了西非季风内大规模动态引发的季节内土壤湿度-大气反馈。令人惊讶的是，尽管萨赫勒地区对强对流的地表响应是短暂的（数天）并且降水积累在空间和时间上不均匀，但观察到对季节内变化的一致的区域尺度地表响应。然后，这种表面响应反馈到西非季风环流。例如，在干燥的季节内事件期间，萨赫勒地表土壤湿度显着降低，导致地表温度升高 1.5°C，并使季风环流向南移动约 1.5° 纬度。此外，在潮湿天气期间，地表会湿润并变冷，从而导致季风向北移动。除了低空风响应外，非洲东风急流 (AEJ) 也会对由于经向温度梯度变化而导致的地表变化做出响应。例如，干旱期间温度梯度的增加会加剧并使 AEJ 向南移动。低层季风西风和AEJ的联合响应影响低层切变和强对流特征。干旱期间低层切变升高会促进西非南部深层对流的加强。这项研究为西非季风环流对季节内土壤湿度反馈的敏感性提供了新的见解，并鼓励其他地区进行类似的研究。改进对土壤湿度-大气反馈的理解和模型表示有可能改善日常时间尺度之外的预测并增强早期预警系统。
Intraseasonal soil moisture variability has the potential to feed back onto the West Africa monsoon circulation through its influence on surface turbulent fluxes and planetary boundary‐layer characteristics. Using satellite observations and an atmospheric reanalysis, we investigate intraseasonal soil moisture–atmosphere feedbacks triggered by large‐scale dynamics within the West African monsoon. Surprisingly, even though the surface response across the Sahel to strong convection is short‐lived (days) and precipitation accumulations are spatially and temporally heterogeneous, a coherent regional‐scale surface response to intraseasonal variability is observed. This surface response then feeds back onto the West African monsoon circulation. For example, during a dry intraseasonal event, Sahelian surface soil moisture significantly decreases, which elevates surface temperatures by 1.5 °C and shifts the monsoon circulation southward by approximately 1.5° latitude. Also, during a wet event the surface moistens and cools which leads to a northward monsoon shift. Alongside a low‐level wind response, the African Easterly Jet (AEJ) also responds to surface changes due to variations in the meridional temperature gradient. For example, an increased temperature gradient during a dry event intensifies and shifts the AEJ southward. The combined response of low‐level monsoon westerlies and the AEJ impacts low‐level shear and characteristics of strong convection. Elevated low‐level shear during a dry event promotes an intensification of deep convection across southern West Africa. This study provides new insight into the sensitivity of the West African monsoon circulation to intraseasonal soil moisture feedbacks and encourages similar research in other regions. An improved understanding and model representation of soil moisture–atmosphere feedbacks has the potential to improve forecasts beyond daily time‐scales and enhance early warning systems.
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