Long-term variability of Rossby Wave Breaking events over the Indian subcontinent

Abstract

The synoptic scale upper level Rossby wave breaking (RWB) has a great influence on the weather pattern on the underlying regions. The RWB events have been studied extensively in the mid-latitude regions as it is prone to such events which often lead to extreme weather conditions. However, studies are elusive especially over the Indian sub-continent except few cases. RWB climatology and variability on monthly, interannual as well as on decadal scales is still poorly understood over this region. To address these shortcomings, in this study, we have used the reanalysis data and implemented a contour searching algorithm to identify RWB events over the period 1979-2021. Using the implemented algorithm, we have detected 513 RWB events for the study period which we further use to examine RWB climatology and variability over the subcontinent (5-40oN, 55-105oE). Our results suggest a significant increase in the number of RWB events per year during the last  two decades, as well as an increase in the intensity over the northwest region of the Indian subcontinent. We note that the RWB frequently affects the northwest region in winter, which later shows a shift in peak number of occurrences of RWB towards central India at the end of winter. This shift is linked to seasonal changes in the background zonal wind in the upper-troposphere. Also, the monthly climatology of vertical intrusions of the PV streamers indicate that intrusions are stronger during winter than other months. In addition, the role of RWB on the dynamical changes of the atmosphere such as anomalies of wind circulation patterns and moisture content is analyzed using composite analysis. The variability of the RWB events and its linkages with global sea surface temperature particularly conditions in the Pacific Ocean have also been studied.