Topographic Rossby Waves in the Arctic Ocean's Beaufort Gyre
Topographic Rossby Waves in the Arctic Ocean's Beaufort Gyre
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DOI：
10.1029/2018jc014233
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发表时间：
2018-09
期刊：
影响因子：
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通讯作者：
Bowen Zhao;M. Timmermans
中科院分区：
文献类型：
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作者：
Bowen Zhao;M. Timmermans
分析了北冰洋博福特环流中温度和水平速度的5年长时间序列，目的是了解驱动数十天时间尺度上观测到的变化的机制（即，亚惯性）。我们采用的温度和水平速度信号的相干性/相位分析，这表明，亚惯性温度变化引起的垂直偏移的水柱，驱动水平运动横跨倾斜的海底。水柱的垂直位移（由温度信号记录）显示出底部增强的特征（即，向地面衰减），而水平速度异常在主盐跃层以下近似正压。结果表明，在弱垂直衰减的限制下，垂直速度和水平速度的不同特征与地形Rossby波理论是一致的。实质上，线性衰减的垂直速度剖面意味着当水水平移动穿过底部斜坡时，整个水柱随深度均匀地拉伸/挤压。因此，对于均匀分层的深水柱，在相对涡度场的响应（确保位涡守恒）也是均匀的深度，导致所观察到的正压水平速度的变化。普遍的地形Rossby波活动的背景下，讨论了博福特涡旋自旋，耗散和稳定。对北冰洋博福特环流的温度和速度的5年时间序列进行了分析，以了解以数十天为周期发生的水运动的来源。我们发现，垂直的水运动是由水平流驱动的倾斜海底。海底附近的垂直运动最强。另一方面，在深博福特环流的水平运动是近似均匀的深度。我们表明，这些特点是一致的地形Rossby波，这是波与水移动水平跨越海底斜坡。流行的地形Rossby波活动的背景下，不断变化的博福特环流的能量和稳定性进行了讨论。
A 5-year long time series of temperature and horizontal velocity in the Arctic Ocean’s Beaufort Gyre is analyzed with the aim of understanding the mechanism driving the observed variability on timescales of tens of days (i.e., subinertial). We employ a coherency/phase analysis on the temperature and horizontal velocity signals, which indicates that subinertial temperature variations arise from vertical excursions of the water column that are driven by horizontal motions across the sloping seafloor. The vertical displacements of the water column (recorded by the temperature signal) show a bottom-intensified signature (i.e., decay toward the surface), while horizontal velocity anomalies are approximately barotropic below the main halocline. We show that the different characteristics in vertical and horizontal velocities are consistent with topographic Rossby wave theory in the limit of weak vertical decay. In essence, a linearly decaying vertical velocity profile implies that the whole water column is stretched/squashed uniformly with depth when water moves horizontally across the bottom slope. Thus, for the uniform stratification of the deep water column, the response in the relative vorticity field (ensuring conservation of potential vorticity) is also uniform with depth, leading to the observed barotropic horizontal velocity changes. The prevalent topographic Rossby wave activity is discussed in context with Beaufort Gyre spin-up, dissipation, and stabilization. Plain Language Summary A 5-year long time series of temperature and velocity in the Arctic Ocean’s Beaufort Gyre is analyzed to understand the source of water motions that occur with periods of tens of days. We find that vertical water motions are driven by horizontal flows across the sloping seafloor. The vertical motions are strongest near the seafloor. On the other hand, horizontal motions in the deep Beaufort Gyre are approximately uniform with depth. We show that these characteristics are consistent with topographic Rossby waves, which are waves associated with water moving horizontally across a seafloor slope. The prevalent topographic Rossby wave activity is discussed in context with energetics and stabilization of the changing Beaufort Gyre.