夏季亚洲季风区对流活动与高原涡的关系

Relationship between the Convection in the Asian Summer Monsoon Region and Tibetan Plateau Vortices

  • 摘要: 基于1979—2019年夏季OLR月平均数据、ERA5再分析资料及高原涡统计数据集,采用EOF、小波分析、合成分析等统计方法,分析了夏季亚洲季风区对流活动和高原涡系统的时空变化特征及两者的关系。结果表明:(1)1979—2019年夏季对流活动最强的是南亚季风区,东亚季风区最弱;南亚季风区对流强度变化呈现整体同位相变化,东亚季风区呈现南北反位相变化,高原季风区整体为同位相变化。(2)三个季风区的对流活动年际变化较大,东亚、南亚和高原季风区振荡周期分别为4~8 a、2~4 a和3~8 a。(3)夏季对流活动偏强时,夏季高原涡频数增加、强度减弱,更易移出高原。(4)在高原涡的有利年,对流层低层850 hPa来自孟加拉湾和西太平洋的暖湿气流为高原涡发生发展提供水汽条件,中层500 hPa青藏高原主体有西南风和西北风的辐合,高层200 hPa大气负涡度异常偏强易造成气流辐散,这种“高层辐散、低层辐合”的环流形式有利于高原涡的发生发展;不利年则与之相反。

     

    Abstract: Based on the monthly average OLR data, ERA5 reanalysis data and Lin Zhiqiang's ERA-Interim plateau vortex dataset of the summers from 1979 to 2019, the spatiotemporal variation characteristics of convective activity and plateau vortex characteristics in the Asian summer monsoon region and their relationship are analyzed using EOF, wavelet analysis, synthetic analysis and other statistical methods. The results show that: (1) The strongest convective activity in summer from 1979 to 2019 occurred in the South Asian monsoon region, while the weakest was in the East Asian monsoon region. The convection intensity change in the South Asian monsoon region showed an overall in-phase pattern, the East Asian monsoon region showed a north-south anti-phase dipole pattern, and the Tibetan Plateau monsoon region showed an overall in-phase change. (2) The interannual variation of convective activity in the three monsoon regions was significant, and the oscillation periods were 4~8 years in the East Asian monsoon region, 2~4 years in the South Asian monsoon region and 3~8 years in the Tibetan Plateau monsoon region. (3) When the convective activity was strong in summer, the frequency of Tibetan Plateau Vortices increased and the intensity weakened in summer, and they were more likely to move out of the Plateau. (4) The circulation fields of favorable and unfavorable years were analyzed. It was found that the configuration of "upper-level divergence and lower-level convergence" during favorable years was conducive to the occurrence and development of Tibetan Plateau Vortices, while the opposite pattern was observed in unfavorable years.

     

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