摘要
本文研究了南方持续性低温事件的环流特征,并讨论了它与冬季风南北反相模态的关系。南方持续性低温过程与寒潮过程不同。与寒潮过程相比,南方低温事件持续时间较长,发生频率较低。寒潮过程中,中高纬度环流以波列状槽脊形势为主。而南方低温事件中,中高纬度以大型斜脊斜槽为主要影响系统。大型斜脊斜槽导致冷空气主要以西方路径为主,中纬度为平直气流所控制。东亚大槽向北收缩,日本南部地区为正高度距平控制,它对冷空气东移起了阻挡作用,使得南方地区长期处于冷空气控制,造成极端低温主要出现在黄河以南地区。同时,活跃的南支扰动也显著影响南方持续性低温的发生。东亚冬季风通常被视为一个整体。近年来的研究指出,除了南北一致变化模态,冬季风还存在南北反相变化模态。在南方持续性低温事件中,地表风场距平表现出南北变化反相的特征,即北方为偏南风距平控制,南方为偏北风距平控制。这与冬季风分布的南北反相变化的特征相一致。这种类型与北风相联系的南方降温并不是由高纬度强冷空气南下造成的。个例分析的结果也验证了上述结果。
In this paper, atmospheric circulation features for persistent cold spells in southern China are investigated and their connection with the opposite variation mode of East Asian Winter Monsoon（EAWM） in the south and north is discussed. Compared with cold waves, the persistent cold spells in southern China persist longer and occur more frequently. During the cold waves, the ridges and troughs form a typical wave train propagating through the Eurasian continent. During the cold spells, the major East Asian trough retreats to the north. According to locations and orientations of tilted ridges and associated troughs in the large-scale circulation at high–mid latitudes, zonal flows prevail in the midlatitudes over Asia, leading to the so called ＂western path＂ of cold air, i. e. cold airmass mainly come zonally from the west. In addition, the southern part of Japan is dominated by positive height anomalies, which block the cold air in the west and prolong the control of cold air over southern China, and thus lead to a persistent extreme low temperature spell in southern China. Besides, active perturbations in the southern branch of the jet stream also play an indispensable role in the event. In most of the previous studies, the Asian Winter monsoon was taken as a whole. However, recent works have shown that there mainly exist two modes of EAWM anomalies, i. e. the mode with the same sign of anomalies throughout the eastern part of China and that with opposite signs of EAWM anomalies in the south and north. With respect to these cold spells, the anomalous surface wind field is featured by variations with opposite signs, i. e. the north is under the control of anomalous southerly wind, while the south is under the control of anomalous northerly winds. This pattern corresponds to the second type of EAWM variability mode, which is different to the mode with the same sign of variation throughout the eastern part of China. For this mode, the northerly winds that lead to the drop of temperature in southern China are
作者
彭京备
孙淑清
PENG Jingbei SUN Shuqing(International Center for Climate and Environment Sciences, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029)
出处
《大气科学》
CSCD
北大核心
2017年第4期691-701,共11页
Chinese Journal of Atmospheric Sciences
基金
国家自然科学基金41675086
公益性行业(气象)科研专项项目GYHY201406020
国家重点基础研究发展计划项目2012CB417205~~
关键词
东亚冬季风
南北反相模态
南方持续性低温
East Asian winter monsoon
East Asian winter monsoon mode with opposite signs of variation in the south and north
Persistent cold events in southern China
