Extreme spring cold spells in North China during 1961–2014 and the evolving processes

摘要

TThis study presents the major features of extreme spring cold spells (ESCS) in North China during 1961–2014 and the evolving processes. During an ESCS, northern Eurasia is controlled by large-scale positive SLP anomalies and an anomalous anticyclone that continuously transport northern cold air to North China, causing significant, persistent, lower-than-normal daily temperatures. In fact, these positive SLP and anticyclonic wind anomalies begin to appear over northwestern Europe about 10 days prior to the ESCS. The anticyclonic wind anomalies keep moving southeastward and expand to the west of Lake Baikal until two days before the ESCS. Then, the center of the anomalous low-level anticyclone moves over Lake Baikal, inducing northerly wind anomalies that transport cold air into North China. In the following days, as the positive SLP anomalies weaken, the anomalous anticyclone and related northerly winds appear to wane, and the ESCS gradually comes to an end. The results may prove meaningful for the prediction and early warning of ESCSs.摘要华北春季冷事件（俗称‘倒春寒’）对当地冬小麦产量具有显著影响，但相关研究较少。本研究通过对1961–2014年极端春季冷事件（ESCS）的分析，发现ESCS期间，欧亚北部的异常反气旋将北方冷空气源源不断地输送到华北，导致那里出现持续低温。上述环流异常在ESCS发生前10天已经开始出现，之后反气旋式风场距平持续向东南方向移动，导致偏北风距平向华北输送冷空气，ESCS开始。随后，上述环流异常减弱，ESCS在接下来的几天逐渐减弱至结束。上述结果对提高华北春季气温预测具有重要意义。