Impacts of ocean currents on the South Indian Ocean extratropical storm track through the relative wind effect
Impacts of ocean currents on the South Indian Ocean extratropical storm track through the relative wind effect
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DOI：
10.1175/jcli-d-21-0142.1
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发表时间：
2021-08
影响因子：
4.9
通讯作者：
H. Seo;Hajoon Song;L. O'Neill;M. Mazloff;B. Cornuelle
中科院分区：
文献类型：
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作者：
H. Seo;Hajoon Song;L. O'Neill;M. Mazloff;B. Cornuelle
本研究探讨了相对风（RW）的作用（风相对于洋流）在区域海洋环流和热带风暴轴在南印度洋。两个高分辨率的区域耦合模式模拟与/无RW效应的比较表明，最明显的海洋环流响应是显着削弱过于强大的反气旋立涡关闭伊丽莎白港，南非，一个偏向的功能归因于上游的厄古拉斯电流（AC）的retroflection。这打开了一个途径，通过该AC运输的暖盐水质量从副热带，产生显着增加的海表温度（SST），向上的湍流热通量（THF），和赤道SST梯度在Agulhas retroflection区域。这些热力和动力的变化伴随着对流层低层局地斜压性和大气斜压波活动的强烈加强。检查的综合生命周期的天气尺度风暴受到高THF事件表明一个强大的加强远下游的热带风暴。大气的能量学计算表明，来自基流的斜压能量转换是增加涡动有效位能的主要来源，该位能随后被转换为涡动动能，为瞬变斜压波的增长提供了条件。总体而言，结果表明，机械和热的海气相互作用是内在的和不可分割的联系在一起，大大影响了南印度洋的热带风暴路径。
This study examines the role of the relative wind (RW) effect (wind relative to ocean current) in the regional ocean circulation and extratropical storm track in the South Indian Ocean. Comparison of two high-resolution regional coupled model simulations with/without the RW effect reveals that the most conspicuous ocean circulation response is the significant weakening of the overly energetic anticyclonic standing eddy off Port Elizabeth, South Africa, a biased feature ascribed to upstream retroflection of the Agulhas Current (AC). This opens a pathway through which the AC transports the warm and salty water mass from the subtropics, yielding marked increases in sea surface temperature (SST), upward turbulent heat flux (THF), and meridional SST gradient in the Agulhas retroflection region. These thermodynamic and dynamic changes are accompanied by the robust strengthening of the local low-tropospheric baroclinicity and the baroclinic wave activity in the atmosphere. Examination of the composite lifecycle of synoptic-scale storms subjected to the high THF events indicates a robust strengthening of the extratropical storms far downstream. Energetics calculations for the atmosphere suggest that the baroclinic energy conversion from the basic flow is the chief source of increased eddy available potential energy, which is subsequently converted to eddy kinetic energy, providing for the growth of transient baroclinic waves. Overall, the results suggest that the mechanical and thermal air-sea interactions are inherently and inextricably linked together to substantially influence the extratropical storm tracks in the South Indian Ocean.