Vertical Structure of Interannual Variability in Cross-Equatorial Flows over the Maritime Continent and Indian Ocean in Boreal Summer
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This study investigates the vertical structure of variability in the cross-equatorial flows (CEFs) over the Maritime Continent and Indian Ocean in boreal summer, based on three reanalysis datasets: ERA-Interim, JRA-55 and NCEP-2. The results show a high consistency in the interannual variability among the reanalysis datasets, especially between ERA-Interim and JRA-55, while great uncertainty exists in the decadal or long-term changes of CEFs. Further analyses on the interannual variability in CEFs indicate that there is a significant negative relationship between the upper- and lower-level CEFs over the Maritime Continent—that is, the northerlies at the upper level and southerlies at the lower level are both enhanced or weakened. This seesaw pattern is also significantly related to the CEFs over the Indian Ocean at the upper level and lower level (i.e., the Somali jet). This close relationship between the upper- and lower-level CEFs and between the Maritime Continent and Indian Ocean is manifested as the leading mode of equatorial meridional winds in the vertical-zonal section over the Maritime Continent and Indian Ocean. Finally, it is found that ENSO is closely related to the vertical leading mode, and to all the CEFs at the upper and lower levels over the Maritime Continent and Indian Ocean.
Key wordscross-equatorial flows vertical structure interannual variability ENSO
本文基于 ERA-Interim, JRA-55 及 NCEP-2 三套再分析资料研究了北半球夏季海洋性大陆和印度洋上空越赤道气流变率的垂直结构. 结果表明: 三套资料对于越赤道气流年际变率的刻画具有非常强的一致性, 尤其是 ERA-Interim 和 JRA-55. 相比之下, 越赤道气流的年代际及更长时间尺度的变化还存在很大的不确定性. 进一步的分析表明, 海洋性大陆越赤道气流的年际变率在高低空表现出很强的反相关, 即高层向南的经向风与低层向北的经向风同时增强或减弱. 这一反相关关系在印度洋上空也有所体现. 高低空越赤道气流的反相变化是赤道经向风在垂直-纬向平面上年际变率的主模态, 并与 ENSO 密切相关.
关键词越赤道气流 垂直结构 年际变率 ENSO
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This research was supported by the National Natural Science Foundation of China (Grant No. 41721004).
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