Abstract:

Based on observation data and reanalysis data during 1979-2014, the interannual variation of surface air temperature in winter in southwest China and its related influence factors were investigated. The air temperature in winter in southwest China exhibited two main modes, with a uniformly negative value and east-west dipole over the southwest China, respectively. When the whole southwest China was abnormally cold in winter, the amplitude of decreased temperature in the east was obviously stronger than that in the west region. The strong cooling in the east was related to the cold advection caused by the low-level anomalous northeasterly and easterly winds, while the weak temperature drop in the plateau of west southwest China was mainly associated with the increased cloud amount and thus radiation cooling induced by the anomalous upward movement. When the temperature in southwest China showed east-west dipole anomalies, the significant surface air temperature anomalies mainly appeared in the plateau. The significant cooling in the plateau was related to the cold advection caused by the abnormal northeast wind and the increase of cloud amount and radiation cooling due to the abnormal upward movement. The uniformly cooling in the whole southwest China region was strongly associated with the more active blocking high over Ural Mountains and western Siberia, which caused the anomalous northeasterly and easterly winds in the eastern part of southwest China, resulting in stronger cold advection and temperature decreasing here. When the temperature in the plateau of southwest China was significantly lower, the abnormal Middle East jet stream caused wave train to propagate downstream in the subtropical westerly jet, and formed an anomalous cyclonic circulation over the plateau and southwest China, the accompanied stronger cold advection induced by abnormal northeast wind and radiation cooling caused by abnormal upward movement led to significant cooling over the plateau of southwest China. Both modes showed weak correlation with East Asian winter monsoon, Arctic Oscillation and ENSO.

Key words: Key words: winter surface air temperature, southwest China, blocking, Middle East jet stream

摘要： 利用1979—2014年台站观测资料和再分析资料对西南地区冬季气温的年际变率及其主要影响因子进行分析。西南冬季气温年际变化主要存在两种模态：全区一致型和东西反向型。西南冬季一致偏冷时，东部降温幅度明显大于西部，东部强降温与低层异常东北风和偏东风引起的冷平流有关；而西部高原地区较小的气温降幅主要与异常上升运动引起的云量增多和辐射降温有关。当西南地区气温变化表现为东西反位相时，显著的气温异常主要位于西部高原地区，该区域显著降温与其上空异常东北风引起的冷平流和异常上升运动引起的云量增多和辐射降温有关。异常活跃的乌拉尔山和西伯利亚西部区域阻塞高压是影响西南冬季气温第一模态的主要因子，其在西南地区东部造成东北风和偏东风异常，导致更强的冷平流，进而引起该区域气温显著偏低。西南西部高原地区气温显著偏低时，中东急流异常在副热带西风急流中引起向下游地区传播的波列，在高原和西南地区上空形成异常的气旋性环流，伴随的异常东北风冷平流和异常上升运动引起的辐射降温使西部高原地区显著降温。东亚冬季风、北极涛动和ENSO与西南冬季气温年际变化两个模态的联系都较弱。

关键词: 关键词：冬季气温, 西南地区, 阻塞高压, 中东急流