Daily temperature variation in March in East Asia from 1979 to 2020

Recent change in the daily temperature variation (DTV) for March in East Asia is investigated. For this purpose, the effects of atmospheric circulation and global warming on the DTV in the region are analyzed using Japanese 55-year reanalysis data. Among the high-frequency variations in surface air temperature (SAT) during spring, the DTV in March showed a significant, increasing trend in East Asia during the four decades from 1979 to 2020. Composite analysis shows that the above-normal March DTV is associated with the anomalous anticyclonic circulation in the North Pacific and the anomalous cyclonic circulation over Russia. These atmospheric circulation anomalies lead to a greater meridional SAT gradient and tend to cause more mid-latitude pressure systems to pass over East Asia. Ultimately, the SAT in March becomes more variable due to enhanced thermal advection over East Asia. In addition, this pattern of circulation anomalies associated with a large March DTV includes features of a weak East Asian winter monsoon (EAWM) system. Meanwhile, regression analysis results using the EAWM and long-term global warming trend indices suggest that both the large-scale atmospheric circulation and global warming contribute significantly to the March DTV change in East Asia. In particular, heterogeneous warming rates and localized soil drying in East Asia during the study period likely explain the role of global warming on East Asian DTV in March.