Characteristics and dynamics of wind-driven upwelling in the Alaskan Beaufort Sea based on six years of mooring data
Characteristics and dynamics of wind-driven upwelling in the Alaskan Beaufort Sea based on six years of mooring data
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DOI：
10.1016/j.dsr2.2018.01.002
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发表时间：
2019-04-01
影响因子：
3
通讯作者：
Hu, Jianyu
中科院分区：
文献类型：
--
作者：
Lin, Peigen;Pickart, Robert S.;Hu, Jianyu
阿拉斯加博福特海斜坡，连同气象观测和再分析领域，六年的系泊数据，被用来量化的风驱动的上升流和相关的大气强迫的发生。典型的上升流事件，由115个单独的事件合成，揭示了当东风是最强的整个陆架急流是反向的西方。在事件结束时，一个底部增强的，向东流动的“反弹喷流”旋转起来，比正常的陆架断裂喷流更强。跨等深线流具有三层结构，表层为向岸流，水柱中部为离岸流，近底部为向岸流。这是因为反向的陆架坡折急流略微向岸，这阻碍了跨等深线表面的埃克曼输运。垂直积分沿等深线动量平衡支持这一解释，并指出反弹急流是由海面高度的纬向梯度驱动的。在超过三分之二的事件中，大西洋水（AW）上涌到陆架，而对于其余事件，只有太平洋水（PW）上涌。这背后的主要驱动因素是季节性变化的PW-AW界面深度离岸的陆棚休息，这是由当地风应力旋度。在夏季，当PW型事件占主导地位，埃克曼泵与负风应力旋度加深了界面深度，限制进入大西洋层。在今年余下的时间里，当AW事件占主导地位，埃克曼吸力与正风应力旋度提高接口。这些变化是由于两个区域大气活动中心-阿留申低压和博福特高压的影响。
Six years of mooring data from the Alaskan Beaufort Sea slope, together with meteorological observations and reanalysis fields, are used to quantify the occurrence of wind-driven upwelling and the associated atmospheric forcing. The canonical upwelling event, composited from 115 individual events, reveals that when the easterly wind is strongest the entire shelfbreak jet is reversed to the west. At the end of the event a bottom-intensified, eastward-flowing "rebound jet" spins up that is stronger than the normal shelfbreak jet. The cross-isobath flow has a three-layer structure with onshore flow in the surface layer, offshore flow in the middle of the water column, and onshore flow near the bottom. This is because the reversed shelfbreak jet is oriented slightly onshore which overwhelms the cross-isobath surface Ekman transport. The vertically-integrated along-isobath momentum balance supports this interpretation and indicates that the rebound jet is driven by the zonal gradient in sea surface height. During over two thirds of the events, Atlantic Water (AW) is upwelled to the shelfbreak, while for the remaining events only Pacific Water (PW) is upwelled. The primary driving factor behind this is the seasonal variation in the PW-AW interface depth offshore of the shelfbreak, which is controlled by the local wind stress curl. During summer, when PW-type events dominate, Ekman pumping associated with negative wind stress curl deepens the interface depth, limiting access to the Atlantic layer. Over the remainder of the year, when AW events dominate, Ekman suction associated with positive wind stress curl raises the interface. These variations are due to the influence of the two regional atmospheric centers of action - the Aleutian Low and the Beaufort High.