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MJO structure associated with the higher-order CEOF modes

机译：与高阶CEOF模式相关的MJO结构

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摘要

The real-time multivariate Madden-Julian oscillation (RMM; MJO) index has been widely employed to monitor the amplitude, phase, and time evolution of MJO events, as the index is formulated from the leading two combined-empirical orthogonal function (CEOF) modes of daily anomalous OLR and 850- and 200-hPa zonal winds, and the modes describe the MJO dynamics well. These two CEOF modes, however, are known to dominate in power spectra at zonal wavenumber one and may underestimate the power and structure at wavenum-bers 2-5 where many MJO events are also prominent. This study approximated a baseline for MJO by applying bandpass filters to daily anomalies on 30-100 day periods and at 1-5 eastward propagating waves, as slightly different bands led to the same conclusions. Following the procedures to develop the RMM index, the daily anomalous data were derived and subjected to the CEOF analysis with all modes archived for diagnosis. Different numbers of the leading modes were compared in explained variance, standard deviation (STD), and wavenumber power spectra to describe the overall MJO magnitude and structure, and on the Hovmoeller diagrams to represent the evolution of three distinct MJO events. Results show that the two leading CEOF modes explain only a small portion of the power spectra at wavenumbers 2-5. This spectral leakage notably reduces the MJO amplitude, particularly of the OLR in the western Pacific. The CEOF modes 3-10 can withhold power sufficiently such that the anomalies reconstructed by the first 10 modes contribute most of the baseline variance; their structures agree well with the baseline by constituting nearly the same proportion in the region from the central Indian Ocean to the dateline and by providing more complete evolutions of the three MJO events on the Hovmoeller diagrams. Meanwhile, these modes introduce a notable amount of power for the equatorial Rossby and Kelvin waves that are partially embedded in the evolution of MJO. The first 50 of the total 432 CEOF modes retain all variance of the baseline MJO, while those higher than 10 contain less information and more noise and can be discarded. Furthermore, this study indicated that the longitudinal STD of the reconstructed anomalies detects the MJO phases and magnitudes in the western Pacific with more physical meaning and in better agreement with the Hovmoeller diagrams than the RMM-like amplitude. The results provide an integral figure of the MJO structure from the CEOF analysis and a more robust RMM framework for monitoring the MJO's evolution in real time and for validating its numerical forecast and simulations.
机译：实时多元Madden-Julian振荡（RMM; MJO）指标已广泛用于监视MJO事件的幅度，相位和时间演变，因为该指标是由前两个组合经验正交函数（CEOF）构成的OLR以及850和200-hPa纬向日风的异常模式，这些模式很好地描述了MJO动态。但是，已知这两种CEOF模式在1号区域波的功率谱中占主导地位，并且可能低估了2-5号波峰处的功率和结构，在这里许多MJO事件也很突出。这项研究通过将带通滤波器应用于30-100天周期和1-5个向东传播的波中的日常异常来近似MJO的基线，因为稍有不同的频带可以得出相同的结论。按照开发RMM指数的程序，得出每日异常数据，并进行CEOF分析，并存档所有模式以进行诊断。在解释的方差，标准偏差（STD）和波数功率谱中比较了不同数量的前导模式，以描述总体MJO幅度和结构，并在Hovmoeller图表上表示三个不同MJO事件的演变。结果表明，两种主要的CEOF模式仅解释了波数2-5时的一小部分功率谱。这种频谱泄漏显着降低了MJO幅度，特别是西太平洋地区的OLR。 CEOF模式3-10可以充分保留功率，以使前10个模式重构的异常贡献了大部分基线方差。它们的结构与基线基本吻合，在从中部印度洋到日期线的区域中几乎占相同的比例，并通过在Hovmoeller图中提供了三个MJO事件的更完整的演变。同时，这些模式为赤道Rossby波和Kelvin波引入了显着的能量，这些能量部分地嵌入了MJO的演化过程中。总共432个CEOF模式中的前50个保留了基线MJO的所有方差，而高于10个的那些包含较少的信息和更多的噪声，可以将其丢弃。此外，这项研究表明，重建异常的纵向STD可以检测出西太平洋的MJO相位和幅度，其物理意义远大于类RMM幅值，并且与Hovmoeller图的一致性更好。结果提供了来自CEOF分析的MJO结构的完整图，以及一个更强大的RMM框架，用于实时监视MJO的演变并验证其数值预测和模拟。

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  • 来源
    《Climate dynamics》 |2014年第8期|1939-1950|共12页
  • 作者

    Ping Liu;

  • 作者单位

    School of Marine and Atmospheric Sciences (SoMAS), Stony Brook University, 199 Endeavour Hall, Stony Brook, NY 11794-5000, USA;

  • 收录信息
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    MJO; RMM index; CEOF;

    机译：MJO;RMM索引;首席执行官;

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