Influence of tropical-extratropical interactions on the dynamics of extreme rainfall event: A case study from Indian region

Abstract

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.