Enhanced Interannual Variability of the Spring High-Temperature Events Over Northeast China and the Associated Mechanisms

The spring-high temperature events (SHTE) over northeast China (NEC) and the related local atmospheric factors including cloud cover, radiation flux, and soil moisture exhibited an increased interannual variability after 1992/93. Correlation analyses reveal that both the North Atlantic quadrupole sea surface temperature anomalies (NAQSSTA) and the spring Siberian snow depth (SSSD) had a stronger linkage with SHTE since the early 1990s. Additionally, the interannual variability of SSSD also showed an interdecadal increase, which is a key factor in the changes of interannual variability of SHTE. Further analyses showed that the NAQSSTA could excite Rossby wave via increasing low-level atmospheric baroclinicity during 1993–2017. One branch of the wave trains propagated eastward and the other branch propagated northeastward through the Siberian high latitudes, which eventually reached NEC together and resulted in local anomalous anticyclonic circulation and sinking motion. The latter branch could contribute to the low geopotential height and cyclonic anomalies over the Siberian high latitudes, which further favored the increase of snow depth there. Subsequently, the positive snow anomalies facilitate the more occurrences of SHTE by exacerbating the meridional thickness gradient between the polar region and mid-latitudes and then limiting the Arctic cold air to invade into the south. Meanwhile, the positive polar-Eurasian pattern (POL) associated with higher SSSD could guide the Rossby wave train originating from the North Atlantic to propagate northeastward, which is consistent with the SHTE-related wave train path after 1992/93. Model results further reproduce the physical processes that linking the NAQSSTA with SHTE.