夏季印度洋海温偶极子对冬季东亚高空急流的影响研究

The impacts of summer IOD on the winter jet streams in East Asia

基于1979—2019年ERA5、NCEP/NCAR再分析资料及多套海温资料,分析夏季印度洋偶极子模态对东亚高空急流的影响,并对热力动力机制展开探讨。结果表明,当夏季印度洋偶极子为正(负)位相,即夏季印度洋西部出现暖(冷)异常,东部出现冷(暖)异常时,冬季的东亚副热带急流增强(减弱),极锋急流强度减弱(增强)。伴随着印度洋偶极子位于正位相,增强(减弱)的经向温度梯度,加强(减少)的低层大气斜压性和较强(较弱)的瞬变涡动动能,易导致冬季的副热带急流增强(极锋急流减弱)。进一步利用多元线性回归方法定量区分热力和动力因子的相对贡献,夏季印度洋偶极子主要通过热力作用影响两支急流。比较两个动力因子发现,极锋急流的减弱主要以大气斜压性为主,而副热带急流的加强则以涡动动能为主。

Based on ERA5,NCEP/NCAR reanalysis data and several Sea Surface Temperature(SST)datasets from 1979 to 2019,the impacts of Indian Ocean Dipole(IOD)mode on the East Asian upper-level jet stream in summer were analyzed,and the thermal and dynamic mechanism were discussed.Results show that as the IOD is in the positive(negative)phase in summer,which indicates the western Indian ocean is warm(cold)and the eastern Indian ocean is cold(warm).Associated with the positive phase of summer IOD,the East Asian subtropical jet will strengthen in winter,and the polar front jet will weaken.The enhanced meridional temperature gradient,the enhanced the baroclinicity of the lower atmosphere and the strong synoptic-scale transient eddy kinetic energy provided benefit conditions for the enhancement of the East Asian subtropical jet,and vice versa for the weakened polar front jet.Multiple linear regression was used to quantitatively distinguish the relative contributions of thermal and dynamic factors.The dominant factor linking the summer IOD and winter East Asian jet streams is the thermal factor.Comparing the two dynamic factors,the atmospheric baroclinicity is the main factor for the weakened polar front jet,while synoptic-scale transient eddy kinetic energy is the main reason for the strengthened subtropical jet.