Abstract Deciphering the variations in the subtropical westerly jet (STJ) and the subpolar westerly jet (SPJ) over the Southern Hemisphere in Earth’s history will help us to better understand how the westerlies may respond to various external forcings in the future. Using Simulation of Transient Climate Evolution over the past 21,000 years simulations, we demonstrate that the STJ migrated equatorward in the Last Glacial Maximum relative to the present, which followed by abrupt poleward, equatorward, and poleward shifts during the Heinrich Stadial I, Antarctic Cold Reversal, and Younger Dryas, respectively. These large-amplitude fluctuations are controlled by changes in meltwater fluxes and polar ice-sheet topography. During the Holocene, the STJ shows no obvious long-term trend, due to the offsetting effect between increased orbital insolation in austral summer and decreased Antarctic ice-sheet topography. The meridional shift of the SPJ shows an in-phase change with the STJ during the past 21 kyr. In terms of the dynamic mechanisms, the meridional shift of the STJ and SPJ is induced by changes in the meridional temperature gradient and the maximum eddy growth rate, respectively; and is also linked to changes in the mean meridional circulations (that is, the Hadley and Ferrel cells). The modeled meridional shift of the southern westerlies is supported by the results from the Paleoclimate Modelling Intercomparison Project Phase Ⅲ and is consistent with several reconstructions, but it is difficult to constrain robustly by geological evidence as the reconstructed westerlies vary across sites and proxies. Nevertheless, our study provides a possible scenario for the evolution of the southern westerlies during the past 21 kyr and identifies the dominant forcing and the associated mechanisms, which may advance our knowledge on the future behavior of the southern westerlies.

中文翻译：

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过去21000年南半球副热带和副极地西风急流经向偏移的演变

摘要 解读地球历史上南半球副热带西风急流（STJ）和副极地西风急流（SPJ）的变化，将有助于我们更好地了解西风在未来对各种外力的反应。使用过去 21,000 年模拟的瞬态气候演变模拟，我们证明 STJ 在上次盛冰期相对于现在向赤道迁移，随后在 Heinrich Stadial I、南极冷逆转期间突然向极、赤道和极地移动，和年轻的仙女，分别。这些大幅波动是由融水通量和极地冰盖地形的变化控制的。在全新世，STJ 没有明显的长期趋势，由于南极夏季轨道日照增加与南极冰盖地形减少之间的抵消效应。SPJ 的子午线偏移显示在过去 21 kyr 期间与 STJ 同相变化。在动力机制上，STJ和SPJ的经向位移分别是由经向温度梯度和最大涡流增长率的变化引起的；并且还与平均经向环流（即哈德利和费雷尔单元）的变化有关。模拟的南西风经向偏移得到了古气候模拟比对项目 III 期结果的支持，并且与多次重建一致，但由于重建的西风因地点和代理而异，因此难以通过地质证据进行强有力的约束。尽管如此，