Mean jest, mesoscale variability and eddy momentum fluxes in the surface layer of the Antarctic Circumpolar Current in Drake Passage
Mean jest, mesoscale variability and eddy momentum fluxes in the surface layer of the Antarctic Circumpolar Current in Drake Passage
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DOI：
10.1357/002224007780388694
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发表时间：
2007-01-01
影响因子：
0.5
通讯作者：
Firing, E.
中科院分区：
文献类型：
--
作者：
Lenn, Y. -D.;Chereskin, T. K.;Firing, E.
利用声学多普勒海流剖面仪(ADCP)对德雷克海峡5年128个断面的表层流速进行观测，研究了南极绕极流(ACC)的表层环流。这些观测解决了平均气流的细节，包括平均亚北极锋(SAF)和极锋(PF)和南极锋(SACCF)的多个细丝的地形控制，当ACC流经德雷克通道时，它们汇聚成单一的平均急流。适用于消耗性浴温测温仪的SAF和PF的次表面定义通常与平均射流一致，而SACCF更好地定义为速度而不是温度。由三条重复路径上的跨路径输送估算，表层250米深处的平均输送为27.8+/-1 Sv。涡动量通量是通过集合平均雷诺应力相对于网格欧拉平均流来估算的。由于惯性流的作用，混合层表面涡动动能增强，而在德雷克航道中，涡动动能向极地减小，从接近800 cm(2)的S(-2)到接近200 cm(2)的S(-2)。ADCP EKE估计值在任何地方都明显高于高度学EKE估计值，尽管极地下降的模式是相同的。速度起伏的水平波数谱在250-330公里范围内达到峰值，并且具有明显的各向异性。在波长小于250公里时，沿通道波动占主导地位；在波长大于250公里时，交叉通道波动占主导地位。中尺度涡旋在德雷克海峡北部的变化中占主导地位。惯性变率随纬度变化不变，与斜压潮汐一起解释了ADCP表层EKE和高度计推断的EKE之间的部分差异，但不是全部。
High-resolution Acoustic Doppler Current Profiler (ADCP) observations of surface-layer velocities in Drake Passage, comprising 128 sections over a period of 5 years, are used to study the surface-layer circulation of the Antarctic Circumpolar Current (ACC). These observations resolve details of the mean flow including the topographic control of the mean Subantarctic Front (SAF) and the multiple filaments of the Polar Front (PF) and Southern ACC Front (SACCF) that converge into single mean jets as the ACC flows through Drake Passage. Subsurface definitions of the SAF and PF applied to expendable bathythermograph temperatures generally coincide with mean jets, while the SACCF is better defined in velocity than temperature. The mean transport in the top 250-m-deep surface layer, estimated from the cross-track transport along three repeat tracks, is 27.8 +/- 1 Sv.Eddy momentum fluxes were estimated by ensemble averaging Reynolds stresses relative to gridded Eulerian mean currents. Eddy kinetic energy (EKE) is surface intensified in the mixed layer because of inertial currents and decreases poleward in Drake Passage, ranging from similar to 800 cm(2) s(-2) to similar to 200 cm(2) s(-2). ADCP EKE estimates are everywhere significantly higher than altimetric EKE estimates, although the pattern of poleward decrease is the same. Horizontal-wavenumber spectra of velocity fluctuations peak at wavelengths in the 250-330 km range and are significantly anisotropic. Along-passage fluctuations dominate at wavelengths less than 250 km; cross-passage fluctuations dominate at wavelengths greater than 250 km. Mesoscale eddies dominate the variance in northern Drake Passage. Inertial variability is constant with latitude and together with baroclinic tides accounts for some but not all of the discrepancy between the ADCP surface-layer EKE and altimetry-inferred EKE.