This study investigates the sub-synoptic scale circulation aspects associated with the extreme rainfall event occurred over the North Indian state of Uttarakhand located in the western Himalayas (WH) during the 15–18 June 2013 period. A diagnosis based on hourly ERA5 reanalyzed circulation products archived on finer grids reveals that sustenance of heavy rains during the event period is supported by a propensity of cyclonic vorticity sources channeled toward the WH region through a narrow quasi-steady conduit in the lower troposphere from the ISM circulation. The equatorward segregating mesoscale potential vorticity (PV) structures from the quasi-stationary upper level PV anomaly (trough) during the event administered two pathways for vorticity sources. The first pathway is from the base of the trough culminating into longer horizontal conduit path from the western Arabian Sea, lending perpetual cyclonic vorticity support to the ISM environment. The second pathway is from the right flank of the trough, which promotes sustained environment of deeper mesoscale convergence zone, potentially unstable atmosphere and strong ascent over the Uttarakhand region. The convergence zone is potentially viewed as a region for strong monsoon and extratropical circulation interactions to occur on finer horizontal scales of motion, where significant vertical synchronization of positive PV advection is realized during the 16–17 June 2013 period. In addition to orographic precipitation enhancements, deeper advective synchronization noticed at sub-synoptic time periods is accredited to the nearly doubling 24-h rainfall amounts in the foothill region of Uttarakhand during the event period. The ERA5 diagnosed diabatic heating additionally indicates that precipitating systems at higher (foothill) elevations contribute to upper (lower) tropospheric heat sources.

中文翻译：

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2013 年 6 月喜马拉雅极端降水事件的亚天气环流变率

本研究调查了与 2013 年 6 月 15 日至 18 日期间发生在位于喜马拉雅山西部 (WH) 的北印度北阿坎德邦极端降雨事件相关的亚天气尺度环流方面。基于存档在更精细网格上的每小时 ERA5 重新分析环流产品的诊断表明，事件期间大雨的维持得到了气旋涡旋源的支持，这些涡旋源通过从对流层低层中的狭窄准稳定管道引导至 WH 区域。 ISM 流通。在事件期间，赤道分离中尺度位涡 (PV) 结构与准静止上层 PV 异常（槽）管理两种涡源途径。第一条路径来自海槽底部，从阿拉伯海西部延伸到更长的水平管道路径，为 ISM 环境提供永久的气旋涡度支持。第二条路径来自槽的右翼，这促进了更深的中尺度辐合带、潜在的不稳定大气和北阿坎德邦地区的强烈上升的持续环境。辐合带可能被视为在更精细的水平运动尺度上发生强季风和温带环流相互作用的区域，在 2013 年 6 月 16 日至 17 日期间实现了显着的正 PV 平流垂直同步。除了地形降水增强，在亚天气时期注意到的更深的平流同步被认为是事件期间北阿坎德邦山麓地区 24 小时降雨量几乎翻了一番。ERA5 诊断出的非绝热加热还表明较高（山麓）海拔的降水系统有助于上（下）对流层热源。