Quantifying the Contribution of Ocean Dynamics to SST Anomaly Formation

这项研究的目的是利用观测数据确定混合层水平平流在产生从月到年际时间尺度的海表面温度异常中的作用。主要关注的是通过地转流异常来量化气候SST梯度的平流，以及在气候混合层中产生的SST异常(SSTA)信号。这一信号令人感兴趣的问题是，海温异常是否可以提前几个月或更长时间预测。也有强有力的证据表明，可以用目前的观测数据来测量它。第二个目标将是量化平均地转流在SSTA平流中的作用。研究区域将是从南纬65度到南纬5度，北纬5度到北纬65度的全无冰深水区域。所调查的空间尺度将从经纬度几度到洋盆尺度(尽管平流热通量将被分辨到几十公里，如下所述)。对于第二个目标，由于数据的限制，许多地区的平流热通量分辨率将被限制在数百公里以上的尺度上。将确定混合层、地转平流产生的SSTA方差的空间分布和比例。平流热通量的空间分辨率前所未有：平流的估计将基于T/P任务卫星地面轨道勾勒出的进入网格单元的平流热通量，此后称为钻石网格单元。这使得可以利用从T/P任务及其后续计划JASON-1(从2002年1月开始提供的数据)获得的沿轨海面高度异常(SSHA)数据来估计地表地转流。与以往使用网格高度计数据的研究相比，该方法避免了网格固有的空间内插的必要性。对于涉及使气候SST平流的洋流异常的主要目标而言，这可使空间分辨率提高约一个数量级。(时间上的插补，最多5天，是不可避免的。本文提供了内插误差和高度计误差的定量评估。)将评估不同的SST产品，包括从NASA/NOAA AVHRR海洋探路者SST数据集获得的名义上9公里分辨率的气候学SST。将对流项进行时间积分，得到每个菱形网格单元对SSTA的平流贡献。通过比较强迫项的相对大小或方差，可能会产生关于SSTA强迫项的相对重要性的误导性图景。这是因为不同强迫项的解相关时间差别很大，作者在最近的一篇文章中从理论上解释了这一点，并通过他们对黑潮延伸区的热收支分析进行了验证。时间积分强迫项允许直接评估其对信号方差的贡献。最后，将以新的方式分析每个钻石网格单元由平流产生的海温异常，揭示平流项的不同方面。首先，将其投影到SSTA的主要经验正交函数(EOF)上。这使得人们可以在EOF的基础上量化归因于平流的方差比例。还将对平流产生的海温异常进行EOF分析，以揭示主导的空间格局。最后将对时间和空间尺度的相关性进行评估。更广泛的影响：结果将有助于提供明确的零假设，即气候海温梯度的异常平流在季节到年际的时间尺度上对海温的产生并不重要，或者提供对平流产生的海温的更严格的评估。还将得到关于平均流作用的低空间分辨率结果。总之，这些结果对于指导今后研究世界海洋SSTA及其影响的气候的可变性和可预测性至关重要。

The goal of the study is to use observational data to determine the role of mixed layer horizontal advection in generating sea surface temperature (SST) anomalies from monthly to interannual timescales. The primary concern is in quantifying the advection of the climatological SST gradient by geostrophic current anomalies, and the resulting SST anomaly (SSTA) signal in the climatological mixed-layer. This signal is of interest to the question of whether SST anomalies are predictable months or more in advance. There is also strong evidence that it can be measured with current observational data. A secondary goal will be to quantify the role of the mean geostrophic currents in advecting the SSTA. The region of study will be all ice-free, deep-water from about 65S to 5S and 5N to 65N. The spatial scales investigated, for the primary goal, will range from a few degrees latitude and longitude to ocean basin scale (though the advective heat flux will be resolved to a few 10s of kilometers, as explained below). For the secondary goal the advective heat flux resolution in many regions will be limited to scales larger than hundreds of kilometers due to data limitations. The spatial patterns and fraction of SSTA variance generated by mixed-layer, geostrophic advection will be determined. Unprecedented spatial resolution for advective heat fluxes: estimates of advection will be based upon the advective heat flux into grid cells outlined by the satellite ground tracks of the T/P mission, hereafter the diamond grid cells. This allows for the estimation of the surface geostrophic current with the along track sea surface height anomaly (SSHA) data obtained from the T/P mission (data available from October 1992) and its follow on program, Jason-1 (data available from January 2002). Compared to previous studies using gridded altimeter data, this method avoids the necessity of spatial interpolation inherent in the gridding. For the primary goal involving current anomalies advecting climatological SST this allows for about an order of magnitude improvement in spatial resolution. (An interpolation in time, of up to 5 days, is unavoidable. A quantitative assessment of both interpolation error and altimeter error is provided herein.) Different SST products will be evaluated, including the nominally 9 km resolution climatological SST obtained from the NASA/NOAA AVHRR Oceans Pathfinder SST dataset. The advection term will be time integrated to obtain the advective contribution to the SSTA at each diamond grid cell. A misleading picture of the relative importance of the SSTA forcing terms can arise by comparing the relative magnitude or variance of the forcing terms. This occurs because of the widely different decorrelation times of the various forcing terms, and is explained in theory in a recent article by the authors, and verified by their heat budget analysis of the Kuroshio Extension area. Time integrating a forcing term allows for direct evaluation of its contribution to the signal variance. Finally, the SSTA generated by advection at each diamond grid cell will be analyzed in novel ways, revealing different aspects of the advection term. First it will be projected onto the leading empirical orthogonal functions (EOFs) of SSTA. This allows one to quantify the fraction of variance attributed to advection on an EOF by EOF basis. An EOF analysis of the advection generated SST anomaly will also be performed to reveal the dominant spatial patterns. Finally the dependence upon temporal and spatial scale will be assessed.Broader Impacts: The results will be useful for either providing definitive support of the null hypothesis that anomalous advection of the climatological SST gradient is not important in generating SSTA on seasonal to interannual timescales, or providing a more rigorous assessment of advection generated SST. Low spatial resolution results on the role of mean currents will also be obtained. Together these results will be crucial for guiding future research on the variability and predictability of the World Ocean SSTA and the climate that it influences.