Abstract:
The responses of surface air temperature (SAT) in northern China to the eastern Pacific (EP) and central Pacific (CP) ENSO events during boreal winter are analyzed using reanalysis and observational data as well as specific atmospheric general circulation model (AGCM) experiments. Possible influences of ENSO events on regional cold extremes are also discussed. The North Atlantic Oscillation (NAO) is identified to be a bridge connecting ENSO signal and northern Eurasian temperature anomalies. Results show that ENSO influences northern China winter surface air temperature mainly through modulating the atmospheric circulation over the North Atlantic region, and thus changing the zonal temperature advection over northern Eurasia and the intensity of Siberian High. Moreover, the ENSO effects display prominent nonlinear characteristics due to different distributions of the tropical Pacific sea surface temperature (SST) anomalies during the two types of ENSO events. Corresponding to the two types of El Niño and EP La Niña winters, negative NAO-like atmospheric anomalies are evident over the North Atlantic region, which tend to inhibit the transport of warm and moist air from the Atlantic Ocean to Eurasian continent and thus favor a colder than normal winter in northern China. In particular, significant negative temperature anomalies during CP El Niño and EP La Niña winters are located in northeast China and the Ordos Loop and its vicinity area, respectively. The significant cold signal is confined in the north of Heilongjiang Province and the Greater Khingan Range during EP La Nia winters. In contrast, a positive NAO-like atmospheric anomaly pattern occurs over the North Atlantic region during the CP La Niña winter, but its positive anomaly center shifts westward. As a result, significant temperature anomalies are mainly confined in Europe and few significant signals can be observed in northern China. These observed results can be realistically reproduced by AGCM experiments. In addition, daily temperature in northeastern China tends to be colder than normal during EP El Niño and CP El Niño winters, indicating more frequent cold extremes. However, the linkage between La Niña events and cold extremes seems to be negligible.