大气低频振荡对2015年冬季华北强降温事件的影响

利用1980—2016年中国日最低温度和NCEP/NCAR再分析资料，分析了大气低频振荡对华北2015年冬季区域强降温事件（Regional Extremely Cold Event，简称RECE）的影响。结果表明：1）两次过程均与最低温度10～20 d低频分量从峰到谷值的变化相应。2）第一（二）次过程巴尔喀什湖-贝加尔湖（简称巴-贝湖）高压位置偏西（偏东北），西伯利亚高压偏南（偏北），东亚大槽呈东北-西南（南-北）走向，阿留申低压偏深（偏西偏深），无（有）北极涛动负异常，高低层冷空气源地均位于贝湖北部60°N附近（巴湖以北上空和华北局地），降温较慢（快速）。地中海低频扰动能量的持续输送是造成两次降温过程持续时间差异的原因之一。3）-18 d （-12 d）500 hPa高度场中西欧低频负（正）异常，是华北强降温事件的延伸期预报参考信号。

The influences of atmospheric low-frequency oscillation on extreme cold events in northern China in the winter of 2015

In this study, based on the daily minimum temperature in China and NCEP/NCAR daily reanalysis data from the period of 1980 to 2016, the influence and its difference of atmospheric low-frequency oscillation on two extremely cold regional events in the winter of 2015 in northern China are investigated.This is done by means of Morlet wavelet analysis, Butterworth band-pass filtering, and time-delay correlation methods.The results of this paper reveal some key low-frequency circulation systems in the upper and lower troposphere, cold air source and path affecting the extremely cold events.This study also extracts the reference signals for the extended-range prediction of the extremely cold events in northern China.The results reveal the following:1) The two regional extremely cooling processes in winter of 2015 correspond to the changes of the 10-20 d low-frequency component of the minimum temperature from peak to valley.2) In the first (second) process, the Lake Balkhash-Lake Baikal high pressure is located to the west (northeast), the Siberian High pressure is to the south (north), the East Asian trough runs northeast to southwest (south to north), the Aleutian Low is westward and deeper, and there is no negative Arctic Oscillation anomaly.The source of cold air in the upper and lower layers is located near 60°N in the northern part of Lake Baikal (above the north of Lake Balkhash and northern China, respectively), and the cooling rate is slower (faster) in the first (second) regional extremely cooling process.The continuous transmission of low-frequency disturbance energy in the Mediterranean Sea is one of the causes of the difference in the duration of the two regional extremely cooling processes.3) The low-frequency negative (positive) anomaly in western Europe at the 500 hPa height field in the-18 d (-12 d) is an important reference signal for predicting the variation of low-frequency East Asian trough (Lake Balkhash-Lake Baikal high-pressure ridge or Lake Baikal high-pressure ridge) and the regional extremely cold events in northern China.