The onset of stratospheric final warming and record–breaking April surface warming over Central Asia in 2022

Abstract

In the spring of 2022, a stratospheric final warming (SFW) event occurred on March 19 at 10 hPa in the Northern Hemisphere, ranking the third earliest SFW event during 1979–2022. Meanwhile, Central Asia recorded the highest surface air temperature (SAT) in the ensuing April in recent 44 years. Based on the fifth generation reanalysis data from European Centre for Medium-Range Weather Forecasts, this study reports an intimate linkage between the SFW onset and the extremely high SAT in Central Asia in April 2022. Specifically, after the SFW onset, positive geopotential height anomalies in the stratospheric polar region persist for more than a month, which propagate downward to the troposphere in about one week, resulting in a negative phase of the Northern Annular Mode (NAM) in the upper troposphere during the period from late March to mid-April. Such a negative NAM tends to excite an anomalous Rossby wave train propagating southeastward from the North Atlantic to Central Asia, causing an anomalous high over Central Asia in the middle and upper troposphere. As a result, the associated anomalies in descending motion and adiabatic heating would lead to the in situ unprecedented high SAT in April.