Vertical and horizontal structures of the North Pacific subtropical gyre axis
Vertical and horizontal structures of the North Pacific subtropical gyre axis
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DOI：
10.1007/s10872-015-0301-9
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发表时间：
2015-05
影响因子：
2.3
通讯作者：
Masafumi Kimizuka;F. Kobashi;Atsushi Kubokawa;N. Iwasaka
中科院分区：
文献类型：
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作者：
Masafumi Kimizuka;F. Kobashi;Atsushi Kubokawa;N. Iwasaka
利用Argo浮标观测资料和几种风应力产品，研究了北太平洋副热带环流的平均结构，重点研究了环流轴，它是副热带环流北方部分向东运动和南方部分向西运动之间的大尺度边界。东、西180°左右的区域内，涡旋轴结构不同。在西部，涡旋轴受到强烈的黑潮延伸急流的影响，显示出与Sverdrup平衡和通风温跃层理论所预期的特征不一致。在东部，深度积分的地转环流在25°N和30°N附近显示出两个涡旋轴，并伴有局地气旋性风应力旋度异常。根据斯维尔德鲁普平衡，两个环流轴应该向西延伸穿过副热带环流，但实际的地转环流只有一个在30°N以西的环流轴。副热带环流的垂直结构表现为：在东部，环流轴随深度显著北移，这与环流轴周围密度层厚度向南减小相一致;而在西部，环流轴沿着黑潮延伸体南翼，北移不太明显。由于CMW的水平均匀性，在CMW层中，环流的移动相对较小，这表明CMW对副热带环流的大尺度环流有动力作用。
Mean structures of the North Pacific subtropical gyre are investigated using Argo float observations and several wind stress products, with a particular focus on the gyre axis, which is defined as a large-scale boundary between eastward motions on the northern part of the subtropical gyre and westward motions on the southern part. Structures of the gyre axis are different between the regions east and west of about 180°. In the west, the gyre axis is affected by the strong Kuroshio Extension jet, showing discrepancy with features expected from the Sverdrup balance and ventilated thermocline theory. In the east, depth-integrated geostrophic circulation displays the two gyre axes at about 25°N and 30°N in association with a local cyclonic wind stress curl anomaly. It is expected from the Sverdrup balance that the two gyre axes would extend to the west across the subtropical gyre, but the actual geostrophic circulation exhibits only one gyre axis around 30°N to the west. The vertical structure of the subtropical gyre exhibits a remarkable northward shift of the gyre axis with depth in the east, consistent with the southward decrease in the thickness of density layers around the gyre axis, while the northward shift is less obvious in the west, where the gyre axis lies along the southern flank of the Kuroshio Extension. The gyre shift is relatively smaller in the central mode water (CMW) layer due to the horizontal uniformity of the CMW, suggesting a dynamic effect of the CMW on large-scale circulations of the subtropical gyre.