青藏高原东部冬季降水对北极涛动异常的响应

Response of winter precipitation in eastern Tibetan Plateau to Arctic Oscillation

中文关键词:  北极涛动  青藏高原东部  东亚季风  南支槽  地形

英文关键词:AO  Eastern TP  East Asian winter monsoon  Southern Branch Trough  Topography

中文摘要:

      基于1979—2015年中国区域CN05.1格点降水以及全球降水气候中心（GPCC）降水等数据资料，采用回归、合成分析等方法，分析了青藏高原东部（简称高原）冬季降水的南、北区域性差异及其年际变化对北极涛动（AO）异常的响应。结果表明：（1）高原北部和南部冬季降水都与AO异常存在密切关系，但降水的年际变化并不一致，对AO异常响应的机理也不同。（2）高原北部冬季降水变化主要和东亚冬季风有关，AO正（负）异常时东亚冬季风减弱（增强），高原北部对流层各层均为东南（西北）风距平，有（不）利于西太平洋的水汽进入高原北部，导致北部降水增加（减弱）。（3）高原南部冬季降水变化主要和南支槽有关，AO正（负）异常时南支槽加强（减弱），有（不）利于源自孟加拉湾的水汽北上高原，低层辐合（散）高层辐散（合），上升（下沉）运动增强，导致南部降水增加（减弱）。简言之，AO通过影响东亚冬季风（南支槽），进而影响高原北（南）部冬季降水，但AO负异常对高原冬季降水的影响比AO正异常的影响更加显著。

英文摘要:

      In this study, regional differences in precipitation between the northern and southern Tibetan Plateau (hereafter TP) are analyzed based on the China gauge-based monthly gridded data (CN05.1) and the precipitation dataset provided by the Global Precipitation Climatic Center (GPCC) for the period 1979 to 2015. Responses of interannual variation in precipitation to the Arctic Oscillation (AO) anomalies are explored using the methods of regression analysis and composite analysis etc. The results indicate that there exists a close relationship between winter precipitation over the northern and southern TP and the AO. However, interannual variations of precipitation in the northern and southern TP and their response mechanisms to AO anomalies are different. Besides, the main synoptic systems that influence winter precipitation in the two regions are also different. The variation of winter precipitation in the northern TP is mainly related to the East Asian winter monsoon, which weakens (strengthens) with southeasterly (northwesterly) anomalies in the troposphere when the AO is in positive (negative) phase. The southeasterly (northwesterly) anomalies are favorable (unfavorable) for water vapor transport from the western Pacific to the northern TP, leading to increases (decreases) in precipitation there. In contrast, winter precipitation anomalies in the southern TP are mainly caused by the southern branch trough. When the AO is in positive (negative) phase, the southern branch trough reinforces (weakens), which is (is not) conducive to the transport of warm and moist water vapor from the Bay of Bengal to the TP and the convergence (divergence) in the lower troposphere. Meanwhile, the ascending (descending) motion enhances, resulting in increased (decreased) precipitation in the southern TP. In summary, the response mechanisms of winter precipitation in the northern and southern TP to the AO anomalies are different in that the AO mainly affects winter precipitation in the northern (southern) TP by affecting the East Asian winter monsoon (southern branch trough). Note that compared to positive AO anomalies, the impact of negative AO anomalies is more significant.