Variability of Warm Season Surface Air Temperature over Northeastern China and Its Relationships with Sea Surface Temperature and Large-scale Atmospheric Circulation Pattern

The warm season is defined as the months from May to September and the variability of warm season surface air temperature (WSAT) over northeastern China (NEC) and its corresponding regional atmospheric circulation are investigated based on monthly average temperature from Climatic Research Unit Version 3.24 and reanalysis data from the NCEP/NCAR dataset for the period of 1980-2014. The results show that there are two major modes of the WSAT over NEC, with the first mode describing a homogeneous structure and the second mode describing a seesaw pattern. These two modes explain 78.2% and 8.6% of the variance, respectively. The first mode exhibits obvious interdecadal variation characteristics with an abrupt shift in the mid-1990s, while the second mode shows both interannual and interdecadal variabilities. The consistent WSAT warming in the whole NEC corresponds to positive 500-hPa geopotential height anomaly and 850-hPa anticyclonic anomaly over NEC, while the seesaw pattern of WSAT over the NEC corresponds to 500-hPa geopotential height anomalies that are opposite in the northern and southern parts of NEC. Further analysis shows that the first mode and its shift in the mid-1990s are closely related with sea surface temperature (SST) anomalies in the Sea of Japan and the Kuroshio extension as well as the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO). SST anomalies over the western Pacific to the east of the Philippines, the central North Pacific, the southeastern coast of China, and the North Atlantic near the northeastern North America all have implications for the prediction of WSAT in NEC. The second mode is closely associated with SST anomaly in the Kuroshio Extension, but has no significant relations with global climate indices. Before the abrupt shift in the mid-1990s, the second mode is affected by ENSO events. After that, the impacts of ENSO are not significant.