北半球中高纬度低频振荡对2012/2013年冬季中国东北极端低温事件的影响

Impacts of the Low-Frequency Oscillation over the Extra-tropics of the Northern Hemisphere on the Extreme Low Temperature Event in Northeast China in the Winter of 2012/2013

利用NCEP／DOE的逐日再分析资料和国家气象信息中心的常规观测站温度资料，首先分析了2012／2013年冬季中国东北区域极端低温事件过程中区域平均温度的低频振荡变化特征，然后分析了北半球中高纬度对流低层和中层低频环流系统配置的变化及其与东北地区强冷空气活动过程的联系，最后进一步研究了中高纬度低频环流系统的传播特征及其对温度变化的影响。主要结果有：（1）2012／2013年冬季东北区域平均温度存在很强的30～60d的周期振荡特征，同时伴随较强的10-30d低频振荡，后者与实际降温过程对应关系更好：（2）对10-30d的低频振荡而言，在东北地区低频温度变化降低最大的位相7（位相3升高最大），500hPa上，我国东部地区正好处于贝加尔湖地区的低频高压（低压）环流和日本海的低频低压（高压）环流型之间的低频偏北（偏南）的较强引导气流中；同时在850hPa上，我国东部从东北到南海都是较强的偏北（偏南）低频风控制，这使得东亚冬季风环流系统加强（被抑制），东北区域则经历一次大幅度的低频温度降低（升高）过程，这些高低空低频环流系统的配置和演变导致了2012／2013年冬季一次次强（或较强）的冷空气沿偏东偏北的路径影响我国东北地区，并导致极端低温事件的出现；（3）沿着乌拉尔山-贝加尔湖-我国东北地区-西北太平洋传播的500hPa低频波列，是驱动2012／2013年冬季东亚冬季风低频振荡和我国东北地区极端低温事件的环流系统。

Using daily data of NCEP/DOE reanalysis II and the temperature data collected at conventional observation stations of National Meteorological Information Center, the characteristics of the low-frequency oscillation （LFO） of the regionally averaged temperature during the extreme low temperature event in Northeast China in the winter of 2012/2013 is analyzed. Changes in the spatial configuration of low-frequency circulation systems in the mid- and lower troposphere in the extratropics of the Northern Hemisphere and their linkage with cold air activities are analyzed. Furthermore, the propagation character of the low-frequency circulation systems and their impacts on temperature changes are also investigated. Results show that： （1） the regionally averaged temperature in Northeast China in the winter of 2012/2013 exhibits a strong 10-30-day oscillation feature, which is accompanied by a significant 30-60-day oscillation and closely related to actual temperature drops. （2） for the 10-30-day oscillation, the phase 7 （phase 3） corresponds to maximum decrease （increase） in temperature over Northeast China; Northeast China is under control of the strong northerly （southerly） air current between the low-frequency high （low） pressure system around Lake Baikal and low-frequency low （high） pressure system nearby the Sea of Japan at 500 hPa; meanwhile, East China from the north to the South China Sea is mainly controlled by low-frequency northerly （southerly） wind at 850 hPa, which strengthens （suppresses） the circulation system of East Asian winter monsoon. As a result, Northeast China undergoes a cooling （warming） process. With such a spatial configuration and evolution of low-frequency circulation systems in the mid- and lower troposphere, Northeast China is affected by strong （or stronger） cold airmass that follows an easterly and/or northerly path and extremely low temperature event happens. （3） A low-frequency wave train at 500 hPa propagates along the path of Urals-Baikal Lake-Northeast China-western Pacific. It is the circulation system that actuates the LFO of East Asian winter monsoon and the extreme low temperature event in Northeast China.