MEAN ZONAL MOMENTUM BALANCE IN THE UPPER AND CENTRAL EQUATORIAL PACIFIC-OCEAN
MEAN ZONAL MOMENTUM BALANCE IN THE UPPER AND CENTRAL EQUATORIAL PACIFIC-OCEAN
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DOI：
10.1029/94jc00033
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发表时间：
1994-04-15
影响因子：
3.6
通讯作者：
LUTHER, DS
中科院分区：
文献类型：
--
作者：
JOHNSON, ES;LUTHER, DS
我们利用夏威夷-塔希提岛航天飞机实验一年的声波多普勒电流剖面仪速度和电导率-温度-深度剖面仪密度来研究热带太平洋中部的平均纬向动量平衡。除垂直应力外，平均流场、年循环流场和高频流场的所有重要贡献都是确定的。我们发现，即使忽略垂直应力，在南纬4度至北纬10度的所有纬度上，纬向动量方程在90-117 m深度处大致平衡。虽然正式的误差条很大，但这种粗略的平衡在四到五个独立的纬度上是可重复的，因此可能是真实的。90米深处的天平是地转的，与赤道的距离在5度以内。在赤道附近，经向平均辐合和经向涡旋应力是平衡平均压力梯度的重要力量。在地表附近，纬向动量方程主要由赤道附近的东向压力梯度和一个向北2度的强Ekman流的东向科里奥利力所主导。在垂直积分中，这些力大致平衡了地面风应力；因此，垂直应力足以关闭我们的动量预算。我们得出的结论是，由风强迫引起的平均垂直应力不会穿透到热带海洋的深度超过90米。这与早先对赤道纬向动量收支的研究相矛盾，但与赤道湍流耗散测量相一致。以前赤道上更强、更深的耗散的发现可能是由于那里更强、更深的平均剪切，而不是由于局部改变的应力剖面。从我们的观测中得到的垂直湍流粘度与以前在赤道上的观测结果一致，但与赤道外常规的理查德森数参数化相矛盾。
We examine the mean zonal momentum balance in the tropical mid-Pacific using a year of acoustic Doppler current profiler velocities and conductivity-temperature-depth profiler densities from the Hawaii-to-Tahiti Shuttle Experiment. All significant contributions from the mean, annual cycle, and higher-frequency flow fields are determined with the exception of the vertical stresses. We find that even neglecting vertical stresses, the zonal momentum equation is in rough balance at 90-117-m depth at all latitudes from 4-degrees-S to 10-degrees-N. While the formal error bars are large, this rough balance is reproducible over four to five independent latitudes and so is probably real. The balance at 90-m depth is geostrophic to within 5-degrees of the equator. Closer to the equator, meridional mean convergence and meridional eddy stresses contribute important forces to balance the mean pressure gradient. Nearer the surface, the zonal momentum equation is dominated by eastward pressure gradients near the equator and eastward Coriolis forces from a strong, northward Ekman flow poleward of 2-degrees-N. In the vertical integral these forces roughly balance the surface wind stress; thus vertical stresses suffice to close our momentum budget. We conclude that on average vertical stresses arising from the wind forcing do not penetrate deeper than 90 m into the tropical ocean. This contradicts an earlier study of the equatorial zonal momentum budget but is consistent with turbulent dissipation measurements on the equator. Previous findings of stronger, deeper dissipation on the equator are probably due to the stronger, deeper mean shear there rather than to a locally altered stress profile. Vertical turbulent viscosities derived from our observations agree with previous observations on the equator but contradict the conventional, Richardson number parameterization off the equator.