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On the Warm Water Volume and Its Changing Relationship with ENSO

机译：暖水量及其与ENSO的变化关系

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The interannual, equatorial Pacific, 20℃ isotherm depth variability since 1980 is dominated by two empirical orthogonal function (EOF) modes: the "tilt" mode, having opposite signs in the eastern and western equatorial Pacific and in phase with zonal wind forcing and El Nino-Southern Oscillation (ENSO) indices, and a second EOF mode of one sign across the Pacific. Because the tilt mode is of opposite sign in the eastern and western equatorial Pacific while the second EOF mode is of one sign, the second mode has been associated with the warm water volume (WWV), defined as the volume of water above the 20℃ isotherm from 5°S to 5°N, 120°E to 80°W. Past work suggested that the WWV led the tilt mode by about 2-3 seasons, making it an ENSO predictor. But after 1998 the lead has decreased and WWV-based predictions of ENSO have failed. The authors constructed a sea level-based WWV proxy back to 1955, and before 1973 it also exhibited a smaller lead. Analysis of data since 1980 showed that the decreased WWV lead is related to a marked increase in the tilt mode contribution to the WWV and a marked decrease in second-mode EOF amplitude and its contribution. Both pre-1973 and post-1998 periods of reduced lead were characterized by "mean" La Nina-like conditions, including a westward displacement of the anomalous wind forcing. According to recent theory, and consistent with observations, such westward displacement increases the tilt mode contribution to the WWV and decreases the second-mode amplitude and its WWV contribution.
机译：自1980年以来，赤道太平洋的20℃等温线深度年际变化主要由两种经验正交函数（EOF）模式控制：“倾斜”模式，在赤道太平洋的东部和西部具有相反的符号，并且与纬向风强迫和El Nino-Southern Oscillation（ENSO）指数，以及第二个EOF模式，即横跨太平洋的一个符号。因为在东赤道太平洋和西赤道太平洋，倾斜模式是相反的符号，而第二EOF模式是一个符号，所以第二种模式与暖水量（WWV）相关联，WWV定义为20℃以上的水量等温线从5°S到5°N，120°E到80°W。过去的工作表明，WWV在倾斜模式下领先了2-3个季节，使其成为ENSO的预报器。但是在1998年之后，铅的含量下降了，基于WWV的ENSO预测失败了。作者构建了一个基于海平面的WWV代理，可追溯到1955年，而在1973年之前，它也表现出较小的领先优势。自1980年以来的数据分析表明，WWV导程的减少与倾斜模式对WWV的贡献显着增加以及第二模式EOF幅度及其贡献的显着下降有关。 1973年之前和1998年之后的铅减少时期均以“平均”类似拉尼娜的状况为特征，包括异常强迫向西移动。根据最新理论并与观察一致，这种向西位移增加了倾斜模式对WWV的贡献，并降低了第二模式振幅及其对WWV的贡献。

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    《Journal of Physical Oceanography》 |2014年第5期|1372-1385|共14页
  • 作者

    Lucia Bunge; Allan J. Clarke;

  • 作者单位

    Department of Earth, Ocean and Atmospheric Science, The Florida State University, P.O. Box 3064520, Tallahassee, FL 32306-4520;

    Department of Earth, Ocean and Atmospheric Science, The Florida State University, Tallahassee, Florida;

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