Role of Quasi-resonant Planetary Wave Dynamics in Winter Precipitation Extremes over India’s High Mountain Region

Abstract

Extreme precipitation during winter over the western Himalayas (WH) is associated with western disturbances embedded in sub-tropical westerly jet streams, which are potentially linked to planetary wave dynamics. In this study, we explore a possible connection of quasi-resonant amplification (QRA) to precipitation extremes observed over WH using the global high-resolution reanalysis ERA5 during the period 1979-2019. Precipitation extremes have been identified using percentile approach (peak over threshold) where daily precipitation amount from the entire time series of precipitation exceeds the 95^th percentile threshold at a particular grid point. Our analysis suggests that substantially magnified, quasi stationary mid-latitude planetary waves with zonal wavenumbers 6 to 8 accompany these extremes, highlighting the influence of QRA phenomenon. Furthermore, we also identified a fingerprint for QRA occurrence in terms of the zonally averaged surface temperature field. Lastly, we classified extreme precipitation intensities and various related key variables using k-means clustering and analyzed the wavenumbers associated with different categories. Our results underpin the significant role of the QRA mechanism in amplification of planetary waves, in turn, favoring western Himalayan precipitation extremes. Detailed results will be discussed.

Keywords: Quasi-resonant amplification, zonal wavenumber, precipitation extremes, western Himalayas

*E-mail of corresponding author: rajuattada@iisermohali.ac.in