Dynamics of an Interhemispheric Teleconnection across the Critical Latitude through a Southerly Duct during Boreal Winter*
Dynamics of an Interhemispheric Teleconnection across the Critical Latitude through a Southerly Duct during Boreal Winter*
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DOI：
10.1175/jcli-d-14-00425.1
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发表时间：
2015-09
影响因子：
4.9
通讯作者：
Sen Zhao;Jianping Li;Yanjie Li
中科院分区：
文献类型：
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作者：
Sen Zhao;Jianping Li;Yanjie Li
利用1957/58 ~ 2001/02年40年ECMWF再分析（ERA-40）和NCEP-NCAR再分析资料，研究了从非洲南部到南亚再到北太平洋的南北半球冬季月平均250 hPa流函数场的遥相关特征。经典的Rossby波理论的纬向变化的流动，其中的基本状态纬向风的影响被忽略预测，固定Rossby波不能传播通过东风。为了阐明负责这种半球间遥相关的基本机制，驻波传播的理论基础，考虑到纬向环境流的临界纬度。理论结果表明，在东非，西印度洋和南亚的偏南气流创造了一个路径，为向北传播的驻波在临界纬度。静止波数和群速度分析，射线跟踪，和简单的模型实验应用到近现实的北方冬季平均气流证实，在南部非洲和西印度洋激发的扰动可以传播的临界纬度到南亚通过南风管，然后继续下游沿着北非-亚洲副热带急流。
In this study, an interhemispheric teleconnection pattern across the critical latitude from southern Africa through South Asia to the North Pacific was revealed in boreal winter monthly averaged 250-hPa streamfunction fields obtained from both the 40-yr ECMWF Re-Analysis (ERA-40) and the NCEP–NCAR reanalysis data from 1957/58 to 2001/02. Classical Rossby wave theory for zonally varying flow in which the effects of the basic-state meridional wind are ignored predicts that stationary Rossby waves cannot propagate across easterlies. To elucidate the underlying mechanisms responsible for this interhemispheric teleconnection, the theoretical basis for stationary wave propagation across the critical latitude is considered, taking into account meridional ambient flow. The theoretical results suggest that the southerly flow over East Africa, the western Indian Ocean, and South Asia creates a path for the northward propagation of stationary waves across the critical latitude. Stationary wavenumber and group velocity analysis, ray tracing, and simple model experiments applied to nearly realistic boreal winter mean flows confirm that disturbances excited in southern Africa and the western Indian Ocean can propagate across the critical latitude to South Asia through the southerly duct and then continue downstream along the North African–Asian subtropical jet.