The northward shrinkage of the North Pacific western subarctic gyre (WSAG) in the early 2000s is associated with a sea surface height (SSH) elevation and is correlated to sea surface wind stress change. By using a Rossby wave model forced by wind stress, which computes the component variations due to the barotropic and first to fourth baroclinic modes, we estimated decadal changes in SSH and main pycnocline depth in the subpolar region. Realistic decadal SSH elevation and deepening of the main pycnocline depth associated with the northward shrinkage of the western subarctic gyre from the late 1990s to the mid-2000s were reproduced by the model. The sea surface elevation was caused primarily by the barotropic Rossby wave response to the relaxation of the Ekman suction due to the attenuation of the Aleutian Low by frequent La Niña occurrences after the late 1990s in addition to the long-term weakening of the westerly wind. The northward shrinkage of the WSAG was found to be associated with the intensification of an anticyclonic circulation centered around 43–44 ^∘ N, 170–175 ^∘ E. The westerly wind weakening deepened the main pycnocline in the western subarctic region through the baroclinic Rossby wave mode response to the wind stress change, which mostly accounts the equivalent halocline deepening at station K2 (47 ^∘ N, 160 ^∘ E). While the first baroclinic mode variation of the water density significantly attenuates during propagation, the higher mode variations, particularly the second and third mode variations, are locally excited through a quasi-resonant amplification mechanism and have profound impacts on the depth of the upper main pycnocline.

中文翻译：

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西北极北太平洋风驱动年代际海面高度和主要比奥克林线深度变化

2000年代初期，北太平洋西部北极亚弧回（WSAG）向北收缩与海面高度（SSH）升高有关，并且与海面风应力变化有关。通过使用由风应力强迫的Rossby波模型，该模型计算了由于正压模式和第一至第四斜压模式引起的分量变化，我们估算了SSH的年代际变化和次极区的主要比索斜线深度。该模型再现了从1990年代末到2000年代中期，现实的年代际SSH升高以及主要的比索线深度的加深与西北极亚回旋的北向收缩有关。海平面升高主要是由于1990年代后期以来频繁发生的拉尼娜事件造成的阿留申低气压的衰减以及西风的长期减弱所致，正气压的罗斯比波对Ekman吸力松弛的响应引起的。发现WSAG的北向收缩与以43-44为中心的反气旋循环的加剧有关^∘N，^170-175∘E。西风减弱减弱了西斜南地区的主要比诺克线，这是通过斜压Rossby波模式对风应力变化的响应而引起的，这主要解释了在K2站上等价的盐线加深（^47∘N， 160 ^∘ E）。虽然水密度的第一斜斜模态变化在传播过程中会显着衰减，但较高的模态变化，特别是第二和第三模态变化，是通过准共振放大机制局部激发的，并且对上部主要比索克林的深度产生了深远的影响。 。