Quantifying the Contribution of Ocean Dynamics to SST Anomaly Formation

量化海洋动力学对海温异常形成的贡献

• 批准号: 0326515
• 负责人: Robert Scott
• 金额: $ 27.56万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-10-01 至 2007-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0326515&HistoricalAwards=false
• 关键词: Quantifying; Contribution; Ocean; Dynamics; SST

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.

本研究的目的是利用观测资料确定混合层水平平流在产生月-年际时间尺度海温异常中的作用。主要关注的是通过地转流异常量化气候海温梯度的平流，以及由此产生的气候混合层海温异常信号。这个信号对于海温异常是否可以提前几个月或更长时间预测的问题很有意义。也有强有力的证据表明，它可以用目前的观测数据来测量。第二个目标将是量化平均地转流在海温平流中的作用。研究区域在南纬65度到5度，北纬5度到65度之间都是无冰的深水区。为实现主要目标，研究的空间尺度将从经纬度几度到海洋盆地尺度（尽管对流热通量将被分解到几十公里，如下所述）。对于次要目标，由于数据的限制，许多地区的对流热通量分辨率将限于大于数百公里的尺度。确定混合层地转平流产生的海温变化的空间格局和分量。平流热通量的空前空间分辨率：对平流的估计将基于T/P任务卫星地面轨迹所勾勒的网格单元的平流热通量，以下为菱形网格单元。这允许用T/P任务（1992年10月的数据）及其后续项目Jason-1（2002年1月的数据）获得的沿迹海面高度异常（SSHA）数据估计地表地转流。与以往的高度计数据网格化研究相比，该方法避免了网格化过程中空间插值的必要性。对于涉及当前异常平流气候海温的主要目标，这允许在空间分辨率上提高大约一个数量级。(最多5天的时间间隔是不可避免的。本文提供了插值误差和高度计误差的定量评估。将评估不同的海温产品，包括从NASA/NOAA AVHRR海洋探路者海温数据集获得的名义上9公里分辨率的气候海温。将对平流项进行时间积分，以获得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幅度或方差，可能会对海温强迫项的相对重要性产生误导。这是因为各种强迫项的去相关时间差异很大，作者在最近的一篇文章中从理论上解释了这一点，并通过他们对黑潮伸展区的热收支分析得到了证实。对强迫项进行时间积分可以直接评估它对信号方差的贡献。最后，将以新的方式分析每个菱形网格单元的平流产生的SSTA，揭示平流项的不同方面。首先将其投影到SSTA的主导经验正交函数（EOFs）上。这允许一个人在EOF的基础上量化归因于平流的方差的分数。对平流产生的海温异常进行EOF分析，揭示其主要的空间格局。最后，对时空尺度的依赖性进行了评价。更广泛的影响：这些结果将有助于为零假设提供明确的支持，即气候海温梯度的异常平流在季节到年际时间尺度上对海温的产生并不重要，或者为平流产生的海温提供更严格的评估。平均电流作用的低空间分辨率结果也将得到。总之，这些结果对于指导未来关于世界海洋SSTA及其影响的气候的变率和可预测性的研究至关重要。