Extremely hot East Asia and flooding western South Asia in the summer of 2022 tied to reversed flow over Tibetan Plateau

Abstract

In the summer (July and August) of 2022, unprecedented heat wave occurred along the Yangtze River Valley (YRV) over East Asia while unprecedented flood occurred over western South Asia (WSA), which are located on the eastern and western sides of Tibetan Plateau (TP). Here, based on observational and reanalysis data, we show evidences that the anomalous zonal flow over subtropical Tibetan Plateau (TP) explains a major fraction of the interannual climate variability over these two regions and the extreme events occurred in 2022. As the upper troposphere over TP is a warm center in summer, anomalous easterly (westerly) flow over TP generates anomalous descent (ascent) on the eastern side of TP and anomalous ascent (descent) on the western side of TP via isentropic gliding. The anomalous easterly flow is extremely strong to reverse the climatological westerly flow over subtropical TP in 1994, 2006, 2013 and 2022. The easterly flow in 2022 is the strongest since 1979, and it generates unprecedented descent (ascent) anomaly on the eastern (western) side of TP, leading to extreme heat wave over YRV and extreme flood over the WSA in 2022. The anomalously strong easterly flow over subtropical TP in 2022 is dominated by internal atmospheric variability related to mid-latitude wave train, while the cold sea surface temperature anomaly over the tropical Indian Ocean increases its strength and the probability of a reversed zonal flow, by reducing the meridional gradient of tropospheric temperature between the tropics and the mid-latitudes.