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Seasonal variability of extratropical North Pacific Wind stress, Ekman Pumping and Sverdrup Transport

机译:温带北太平洋风应力,Ekman抽水和Sverdrup输送的季节变化

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摘要

The annual cycle of the North Pacific wind stress, Ekman pumping and Sverdrup transport is investigated by means of empirical orthogonal function (EOF) analysis techniques. Fifty-two years of National Centers for Environmental Prediction (NCEP, formerly "NMC") and the National Center for Atmospheric Research (NCAR) Reanalysis daily averaged surface wind components covering the extratropical North Pacific are used to calculate daily averaged wind stress components. These wind stress components are averaged to 624 monthly mean fields from which monthly mean Ekman pumping and Sverdrup transport fields are derived. Each data field has the long-term annual mean and linear trend removed at each grid point before EOF analysis. The first three modes are considered to be physically significant based on the plot of the log eigenvalue against its root. The first principal components of each field are highly coherent, have most of their spectral energy at the annual cycle, and are nearly in phase. The second mode of these fields show significant spectral energy at the semiannual cycle. The third mode has more complex spatial variability than the first and second mode. The annual cycle is best described by the first EOF mode which is composed of two seasons (winter and summer) that last for five months each separated by two rapid (approximately one month) transition periods (spring and fall). The annual cycle is complex and certain geographical regions are seasonal "hot spots" that add to the complexity. Relationships are derived between the various modes to help explain seasonal movement of the Ekman pumping zero isotach and seasonal variations in Sverdrup transport. The annual variability can reasonably be described using only the first three EOF
机译:利用经验正交函数(EOF)分析技术研究了北太平洋风应力,埃克曼抽水和Sverdrup输送的年周期。 52年的国家环境预测中心(NCEP,以前称为“ NMC”)和国家大气研究中心(NCAR)的再分析均使用覆盖北太平洋温带地区的日平均地表风分量来计算日平均风应力分量。这些风应力分量平均为624个月平均场,由此可得出Ekman抽水月平均量和Sverdrup输送月平均量。在进行EOF分析之前,每个数据字段都将在每个网格点处删除长期的年平均值和线性趋势。根据对数特征值相对于其根的图,前三种模式在物理上被认为是重要的。每个场的第一个主要成分是高度相干的,在一年周期中具有大部分频谱能量,并且几乎是同相的。这些场的第二种模式在半年周期中显示出显着的光谱能量。与第一和第二模式相比,第三模式具有更复杂的空间可变性。年度循环最好用第一个EOF模式描述,该模式由两个季节(冬季和夏季)组成,每个季节持续五个月,每个季节由两个快速(大约一个月)过渡期(春季和秋季)分隔。年周期是复杂的,某些地理区域是季节性的“热点”,这增加了复杂性。推导了各种模式之间的关系,以帮助解释泵送零等腰线的埃克曼的季节性运动与Sverdrup运输的季节性变化。仅使用前三个EOF可以合理地描述年度变化

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    Moore Christopher S.;

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