摘要:利用NCEP/NCAR全球再分析资料、地面观测资料和自动站降水资料，分析了2018/2019年冬季浙江罕见连续阴雨寡照天气过程中冬季风环流和南支槽等环流异常，并从西风带波动、海温强迫等方面研究了局地环流异常的成因。结果表明：2018/2019年冬季连阴雨事件中雨日、日照破历史记录，雨量较常年同期明显偏多。主要的环流异常为西北太平洋异常反气旋（WNPAC）明显偏北，同时阿留申低压和西伯利亚高压亦偏北，东亚地区40°N以南有强的偏南风异常，冬季风偏弱；南支槽较常年偏强，保证了浙江上空有持续的水汽和扰动输送。对流层中层存在沿欧洲向东亚—西太平洋传播的波动能量，波能在东亚地区一直向南传播至20°N以南，可能导致WNPAC明显北抬和南支槽加强。ENSO是WNPAC的重要强迫源，ENSO暖位相使得海洋性大陆出现异常对流冷却，而浙江上空对流加强，ENSO对南支槽活动强度亦有明显的制约作用。中国近海海温偏高是WNPAC和阿留申低压明显偏北的重要影响因素。2018/2019年冬季局地环流异常可能由ENSO和中国近海海温协同强迫所致。
关键词:连阴雨/
西北太平洋异常反气旋（WNPAC）/
东亚冬季风/
南支槽/
ENSO
Abstract:Based on the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) global reanalysis data, ground observation data, and automatic station precipitation data, this study analyzed circulation anomalies such as winter monsoon circulation and the South Branch trough in rare continuous rain and oligoscale weather in Zhejiang in the winter of 2018/2019. Moreover, the study investigated the causes of local circulation anomalies from aspects such as westerly wind fluctuation and sea temperature forcing. The results showed that in the winter of 2018/2019, the rainy days and sunshine hours surpassed the historical record, and the rainfall was significantly above normal. The main circulation anomalies were the abnormal northerly western North Pacific anomalous anticyclone (WNPAC). Meanwhile, the Aleutian low-pressure and the Siberian high-pressure systems were also northerly. There was a strong southerly wind anomaly south of 40°N in East Asia, and the winter monsoon was weak. The southern branch trough was stronger than the perennial, ensuring that there was a continuous water vapor and disturbance transport over Zhejiang. In the middle layer of the troposphere, a wave energy propagated along Europe to East Asia and the western Pacific. The wave energy spread southward to the south of 20°N in East Asia, which might lead to a significant north lift of the WNPAC and the strengthening of the southern branch trough. The El Ni?o–Southern Oscillation (ENSO) warm phase caused abnormal convective cooling in the maritime continent, while the convection over Zhejiang strengthened, and ENSO also had a significant effect on the activity intensity of the southern branch trough. The high sea surface temperature in the offshore waters of China was an important factor for the WNPAC and the Aleutian Low to significantly jump north. The abnormal circulation in the northern hemisphere in the winter of 2018/2019 might have been caused by ENSO and China’s offshore sea temperature collaborative forcing.
Key words:Continuous rain/
Western North Pacific anomalous anticyclone (WNPAC)/
East Asian winter monsoon/
South branch trough/
ENSO
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