Increasing March Daily Temperature Variation over East Asia: Roles of Atmospheric Circulation and Global Warming

The daily temperature variation (DTV) in March over East Asia (EA) during the period 1979–2020 is examined in this study. Using the JRA-55 dataset, we analyze the respective roles of atmospheric circulation and global warming in modulating regional DTV. Among the high-frequency components of surface air temperature (SAT) variability in spring, March DTV exhibits a statistically significant increasing trend over EA during the four decades. Composite analysis reveals that above-normal March DTV is closely associated with anomalous anticyclonic circulation over the North Pacific and anomalous cyclonic circulation over Russia. These circulation anomalies enhance the meridional SAT gradient and increase the frequency of mid-latitude synoptic-scale pressure systems traversing EA. Consequently, enhanced thermal advection leads to increased variability in March SAT across the region. Furthermore, the circulation anomaly pattern linked to large March DTV displays characteristics consistent with a weakened EA winter monsoon (EAWM). Regression analyses employing indices of the EAWM and the long-term global warming trend indicate that both large-scale atmospheric circulation variability and global warming have contributed significantly to the observed changes in March DTV over EA. In particular, spatially heterogeneous warming rates and localized soil drying during the period are likely key factors explaining the influence of global warming on the increasing March DTV in EA.