Asymmetry in the Arctic Oscillation Teleconnection with January Cold Extremes in Northeast China
HE Sheng-Ping;Climate Change Research Center, Chinese Academy of Sciences;Nansen-Zhu International Research Centre, Institute of Atmospheric Physics, Chinese Academy of Sciences;
The connection of the Arctic Oscillation(AO with the frequency of temperature extremes over Eas Asia during boreal winter has been documented by many studies. This study describes an asymmetry in the rela tionship between the January AO and the simultaneou cold extremes in Northeast China(NEC), and further re veals a breakdown of this relationship. It is demonstrated that the frequency of January cold extremes in NEC shows significant(insignificant) negative correlation with the simultaneous negative(positive) phase of the AO. One possible explanation for such an asymmetry is that the Arctic center of negative AO extends more southwards to Siberia compared with that of positive AO, conducive to a closer connection with the frequency of an extreme Sibe rian high. As a result, the frequency of January cold ex tremes in NEC shows a more significant relationship with the negative AO. The other related explanation is that concurrent with the negative phase of the AO, there is an evident meridional stationary planetary wave in the uppe troposphere around(30°N, 100–300 hP a), which disap pears in the positive AO. Therefore, the negative AO could better reflect the fluctuation of the subtropica westerly wind and the synoptic-scale transient wave ac tivity, which is closely related to the frequency of cold extremes in NEC. Along with a positive polarity of the AO trend since the mid-1980 s, the connection between the cold extremes over NEC and the AO during January has been weakened.