初夏孟加拉湾风暴活动期间青藏高原大气环流的异常特征

ABNORMAL CHARACTERISTICS OF ATMOSPHERE CIRCULATION OF TIBETAN PLATEAU DURING CYCLONIC STORM ACTIVITIES OVER THE BAY OF BENGAL IN EARLY SUMMER

利用1979-2013年美国关岛联合台风警报中心(JTWC)孟加拉湾热带气旋数据以及美国国家环境预报中心和美国国家大气研究中心(NCEP/NCAR)发布的2.5°×2.5°再分析资料、0.5°×0.5°降水格点资料,分析了35年初夏(5月)17个北上孟加拉湾风暴活动期间青藏高原及其周边地区降水、大气环流、水汽和热量收支及其气候异常特征,探讨孟加拉湾风暴活动对青藏高原大气环流的可能影响。结果表明:初夏孟加拉湾风暴活动期间,我国降水主要分布在青藏高原南侧、西南和华南地区,并相对于初夏气候平均表现为正异常。风暴北上过程伴随南亚高压北上,南支槽加深,青藏高原切变系统活跃等环流特征。与初夏平均相比,青藏高原东南部大气上升运动异常增强。同时受北上孟加拉湾风暴水汽和热量输送影响,该区域视热源和视水汽汇呈正异常区,而风暴影响下垂直运动增强是其热量和水汽收支异常的主要原因。

Based on the 2.5° × 2.5° reanalysis data, the 0.5° × 0.5° gridded daily rainfall from the NCEP/ NCAR and the best-track data from Joint Typhoon Warning Center, a study is conducted to investigate the impacts of cyclonic storm activities over the Bay of Bengal on the Tibetan Plateau atmospheric circulation in early summer. The precipitation distribution, atmospheric circulation change, moisture and heat budgets surrounding the Tibetan Plateau area related to 17 northward cyclonic storms （NCS） in May during the years from 1979 to 2013 are composed and compared to the climate mean. Results show that heavy rainfall generally occurs in the south of the Tibetan Plateau, Southwest China and South China during NCS activity periods. There are several rainfall positive anomalies occurring in the south of the Tibetan Plateau, Southwest China and South China re- spectively, compared to the climate mean in May. It is found that the South Asia High moves northward, and the south branch trough develops and the wind shear is active when cyclonic storms approach northward to the Tibetan Plateau. Compared with the mean state of early summer, the ascending motion of the atmosphere strengthens in the southeast of the Tibetan Plateau during the activities of NCS, which is also a positive anomaly area of apparent heat source and apparent moisture sink due to the transportation of water vapor and thermal en- ergy by NCS. The strengthening of ascending motion related to cyclonic storms plays a main role in the anomaly of heat source and moisture sink over the southeast of the Tibetan Plateau.