Abstract/Summary

Western disturbances (WDs) are mid-to-upper-tropospheric mesoscale vortices, which typically propagate along the subtropical westerly jet stream and bring heavy rainfall to Pakistan and northern India during boreal winter. They are dynamically similar to Tibetan Plateau vortices (TPVs), which affect southwest China during spring and summer and emanate from the Tibetan Plateau. Here, we propose that their similarity implies the existence of a more general group of upper-tropospheric vortices featuring interactions with the orography of the Hindu Kush-Himalaya-Tibetan Plateau region. Using existing track databases for WDs and TPVs derived from ERA-Interim reanalysis, we show that their respective occurrence frequencies are highly anticorrelated with each other through the seasonal cycle, yet both are strongly correlated with jet latitude. Our findings imply that the incidence of hazards due to WDs and TPVs is correlated on intra- and interannual timescales, particularly through upper-level baroclinicity.