Objective estimates of westward Rossby wave and eddy propagation from sea surface height analyses
Objective estimates of westward Rossby wave and eddy propagation from sea surface height analyses
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DOI：
10.1029/2008jc005044
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发表时间：
2009-03
影响因子：
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通讯作者：
C. Barron;A. Kara;G. Jacobs
中科院分区：
文献类型：
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作者：
C. Barron;A. Kara;G. Jacobs
介绍了一种估算海面高度向西传播异常的客观方法，并与主观方法进行了比较。两种方法都使用从全球SSH分析中提取的时间序列，通过高度计数据的最佳插值准备，如详细所述。客观方法中使用的代价函数计算沿坡标准差的平均值，其中斜率是传播速度的倒数，并通过SSH时间序列定义沿每个样条的线性样本的角度。沿坡标准差可以作为Radon变换的扩展来计算，如下所示。最佳速度估计使成本函数最小化，平均沿斜率标准差在最小值的1%以内的速度定义了不确定度的范围。选择1%的标准是为了在各种情况下给出一个看似合理的不确定性范围，并不意味着在不确定性范围内真正最小值的特定概率。应用于太平洋中部，客观速度估计从最高纬度的1厘米s - 1或更少增加到赤道附近的30厘米s - 1以上。主观速度估计值与客观速度估计值相似，但通常低于客观速度估计值，这反映了主观解释的偏见，这种偏见可能因个人而异。对160°E-95°W上沿坡最小化的更详细的研究侧重于更高的低纬度速度，在1993-2006年期间，在5.5°N（5.5°s）上的估计为48 cm s - 1 （45 cm s - 1）。相应的42-55 cm s - 1 （38-65 cm s - 1）不确定性范围限制了使用交替预处理滤波器或不同多年时间窗的敏感性测试用例的大多数预测，尽管赤道以南的变异性更大。这些发现与先前的研究一致，并表明这些方法可能对全球海洋的其他应用有用。
[1] An objective method to estimate westward propagation of sea surface height (SSH) anomalies is introduced and compared to a subjective technique. Both approaches use time series extracted from global SSH analyses, prepared by optimal interpolation of altimeter data, as described in detail. The cost function used in the objective method calculates the mean along-slope standard deviation, where slope is the reciprocal of propagation speed and defines the angle of linear samples through the SSH time series along each transect. The along-slope standard deviation can be computed as an extension of the Radon transform, as shown. The optimum speed estimate minimizes the cost function, and speeds with mean along-slope standard deviation within 1% of the minimum define the range of uncertainty. The 1% criteria was chosen to give a seemingly reasonable uncertainty range over a variety of cases and does not imply a specific probability that the true minimum is bounded in the uncertainty range. Applied in the central Pacific, objective speed estimates increase from 1 cm s−1 or less at the highest latitudes to above 30 cm s−1 nearer the equator. Subjective speed estimates are similar to, but generally lower than, their objective counterparts, reflecting a bias in subjective interpretation that is likely to vary among different individuals. A more detailed examination of the along-slope minimization over 160°E–95°W focuses on the higher low-latitude speeds, returning estimates of 48 cm s−1 (45 cm s−1) at 5.5°N (5.5°S) over 1993–2006. The corresponding 42–55 cm s−1 (38–65 cm s−1) uncertainty ranges bound most of the predictions from sensitivity test cases with alternate preprocessing filters or different multiyear time windows, although variability is larger south of the equator. The findings are consistent with prior studies and suggest the methods may be useful for other applications over the global ocean.