京津冀冬季冷空气过程的低频特征及西伯利亚高压低频变化的影响

Low-frequency characteristics of winter-time cold air activity in the Beijing-Tianjin-Hebei region and the impacts of low-frequency variation of the Siberian High

本文使用1981-2015年京津冀地区逐日气温和NCEP/NCAR再分析资料,分析了京津冀地区冬季冷空气过程的低频环流特征,以及西伯利亚高压(SH)的低频变化特征及其对京津冀冷空气过程的影响。分析表明,冬季京津冀气温和SH都存在10~30 d显著低频周期,且二者的低频分量之间存在显著的超前滞后相关。京津冀冷空气过程主要发生在低频气温从零位相到谷值的下降阶段,以及低频SH从峰值到零位相的下降阶段。随着京津冀气温和SH的10~30 d低频变化,亚洲近地面层和中层大气环流均表现出一个从西北向东南传播的低频变化周期。影响京津冀地区的低温异常最早出现在喀拉海附近并在亚洲高纬地区维持和积累,产生持续冷却作用;同时中层相应区域维持的强气旋性环流异常表明有持续的大气辐合,中层辐合下沉与近地面持续冷却作用配合形成近地面异常高压。异常高压伴随异常低温南下过程中与中层加强的东亚大槽配合,使京津冀地区处于整层北风异常中,易形成冷空气过程。

The characteristics of low-frequency oscillation of the cold air activity in the Beijing-Tianjin-Hebei(BTH)region in boreal winter and the impacts of the low-frequency characteristics of the Siberian High(SH)on them are investigated,using daily temperature observational data and NCEP/NCAR reanalysis data with a time span covering 1981-2015,based on power spectrum and composite analysis methods.The results show that both the daily temperature in the BTH region and the SH have a dominant period of 10-30 days in both daily temperature in the BTH region and the SH,and there exist significant lead-lag correlations between the low frequency oscillations of them.The cold surges in the BTH region mainly occur during the descending phase from the zero position to the trough of the low-frequency oscillation of temperature and the descending phase from the peak to the zero position of the low-frequency oscillation of the SH.A low-frequency cycle of abnormal atmospheric circulation propagating from Northwest Asia to Southeast Asia appears near the surface and in the middle layer,along with the low-frequency oscillations of the temperature in the BTH region and the SH.The abnormally low temperature,which affects the BTH region,originates near the Kara Sea and accumulates at the high latitudes of Asia,where a cooling effect is produced continuously.Meanwhile,marked convergent subsidence occurs in the middle layer,owing to the atmospheric convergence caused by the abnormal cyclone at the high latitudes of Asia.The combined effect of the convergent subsidence in the middle layer and the persistent cooling near surface results in an abnormal high,which later enhances and moves southward with the abnormally low temperature near surface.The East Asian Trough in the middle layer intensifies as this abnormal high moves southward,which brings deep-layer northerly wind to the BTH region.As a result,the cold air activity in the BTH region is intensified.