A diagnostic investigation of an extreme rainfall episode that occurred over the central and north Indian region is carried out in this study using data from a suite of observations from space-borne instruments and the reanalysis datasets. This event is unique in the sense that the organized tropical and extratropical forcing stimulated the intense rainfall on 01 Jan 2012. The WindSat (multi-frequency polarimetric microwave radiometer) observations indicate the source of the moisture flux coming from the adjoining tropical Ocean. The dynamical and thermo-dynamical contributions are evaluated based on the atmospheric instability analysis using the Atmospheric Infrared Sounder (AIRS) and reanalysis datasets by computing various stability indices such as total totals (TT) index, Potential Vorticity (PV), static stability and the Convective Available Potential Energy (CAPE). High TT index values (>40 K) are observed both in satellite and reanalysis data indicating thermodynamic instability. PV intrusion to low latitudes is also observed with extreme rainfall occurrence ahead of the PV tongue. The vertical structure of PV intrusion shows remarkable features with enhanced upward motions ahead of the intrusion representing the dynamical instability. The reduced static stability, increased CAPE and upper-level cyclonic anomalies together with enhanced moisture in the lower troposphere coming from the adjoining tropical Indian Ocean regulate the amplitude and region of occurrence of the extreme rainfall. Therefore, this study identifies the significant implications of tropical and extra-tropical influences that generate the thermodynamical and dynamical instabilities for the occurrence of the extreme rainfall event over the Central and Northern parts of India.

中文翻译：

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热带-温带相互作用对极端降雨事件动力学的影响：以印度地区为例

本研究使用来自一系列星载仪器和再分析数据集的观测数据，对印度中部和北部地区发生的极端降雨事件进行了诊断调查。这一事件是独一无二的，因为有组织的热带和温带强迫刺激了 2012 年 1 月 1 日的强降雨。 WindSat（多频极化微波辐射计）观测表明来自相邻热带海洋的水分通量的来源。基于使用大气红外测深仪 (AIRS) 和再分析数据集的大气不稳定性分析，通过计算各种稳定性指数（如总总量 (TT) 指数、潜在涡度 (PV)、静态稳定性和对流可用势能 (CAPE)。在卫星和再分析数据中观察到高 TT 指数值 (>40 K)，表明热力学不稳定。PV 侵入低纬度也被观察到，在 PV 舌之前出现极端降雨。PV入侵的垂直结构显示出显着的特征，入侵前的向上运动增强，代表动态不稳定。静态稳定性降低、CAPE 增加和上层气旋异常以及来自相邻热带印度洋的对流层低层水分增加，调节了极端降雨的幅度和发生区域。所以，