阿拉伯海和印度西部上空对流层中层系统的分类
Classification of Middle Tropospheric Systems over the Arabian Sea and Western India
AI总结：
本文结合无监督机器学习与气旋追踪，将印度西部及阿拉伯海MTCs生成分为四类，揭示其与孟加拉湾气旋活动、季节内振荡相位及降雨强度的关系。
摘要：
本研究利用无监督机器学习算法和气旋追踪，研究了造成印度西部大部分年降水量和极端降雨事件的对流层中层气旋（MTCs）的形成。两种方法都揭示了导致这些系统生成的四种主导天气型；具体而言，即来自孟加拉湾的向西移动天气系统的再度增强（1型，51%）；在阿拉伯海上空原地形成，同时存在一个先于（2a型，31%）或后于（2b型，10%）该生成过程的孟加拉湾气旋系统；最后是在来自南孟加拉湾、向西北传播的气旋异常内原地生成（2c型，8%）。因此，该区域很大一部分带来降雨的对流层中层天气系统，是与孟加拉湾的气旋活动相关联而形成的。所识别出的四种变体还表现出对大尺度环境特征的显著依赖：1型和2a型的形成主要发生在北方夏季季节内振荡的第4和第5相位，而2b型和2c型则发生在第3和第4相位。此外，伴随孟加拉湾气旋异常的原地形成（2a型和2b型）大多出现在6月，而下游发展更可能发生在季风季节的核心期。在所有类别中，2a型与最高降雨率（60毫米/天）相关，并表明孟加拉湾上空的低压系统与印度西部及阿拉伯海东北部MTCs发展之间存在动力相互作用。这种分类、对前兆的识别、与孟加拉湾气旋活动的联系以及对大尺度环境的依赖，为更好地理解和预测印度西部上空带来降雨的MTCs提供了途径。
英文摘要：
The formation of Middle Tropospheric Cyclones (MTCs) that are responsible for a large portion of annual precipitation and extreme rainfall events over western India is studied using an unsupervised machine learning algorithm and cyclone tracking. Both approaches reveal four dominant weather patterns that lead to the genesis of these systems; specifically, re-intensification of westward moving synoptic systems from Bay of Bengal (Type 1, 51%), in-situ formation with a coexisting cyclonic system over the Bay of Bengal that precedes (Type 2a, 31%) or follows (Type 2b, 10%) genesis in the Arabian Sea, and finally in-situ genesis within a northwestward propagating cyclonic anomaly from the south Bay of Bengal (Type 2c, 8%). Thus, a large fraction of rainy middle tropospheric synoptic systems in this region form in association with cyclonic activity in the Bay of Bengal. The four variants identified also show a marked dependence on large-scale environmental features with Type 1 and Type 2a formation primarily occurring in phases 4 and 5, and Type 2b and Type 2c in phases 3 and 4 of the Boreal Summer Intraseasonal Oscillation. Further, while in-situ formation with a Bay of Bengal cyclonic anomaly (Type 2a and 2b) mostly occurs in June, downstream development is more likely in the core of the monsoon season. Out of all categories, Type 2a is associated with the highest rain rate (60 mm/day) and points towards the dynamical interaction between a low pressure system over the Bay of Bengal and the development of MTCs over western India and the northeast Arabian Sea. This classification, identification of precursors, connection with cyclonic activity over the Bay of Bengal and dependence on large-scale environment provides an avenue for better understanding and prediction of rain-bearing MTCs over western India.
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