南美洲热带和亚热带季内变率:常模方法

André S. W. Teruya, V. Mayta, B. Raphaldini, P. S. Silva Dias, C. Sapucci
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摘要

在分析南美洲季内变化(ISV)时,没有使用传统的对特定大气场进行滤波的时空傅里叶分析方法,而是使用了一种正态模式分解方法。分别研究了 30-90 天波段、20-30 天波段和 10-20 天波段的季内变化。在三个波段中,季内时间尺度上最具特征的结构是南大西洋辐合带和南美洲中东部地区之间的偶极对流。在 30-90 天波段,对流和环流模式受到大尺度麦登-朱利安振荡(MJO)的影响。在 20-30 天和 10-20 天波段,对流结构主要受外热带罗斯比波列控制。根据30-90天、20-30天和10-20天ISV对再分析数据进行的常模分解显示,在南美洲上空观测到的对流层环流和CESA-SACZ对流结构主要由旋转模式(即罗斯比波、罗斯比-重力混合波)控制。30-90 天的 ISV 也有相当一部分与惯性重力模式(如开尔文波)有关,主要发生在澳大利亚雨季。所提出的分解方法表明,可以再现现实的环流,为诊断和研究波的动力学以及它们之间的相互作用提供了一个强有力的工具,因为它们能够对观测到的特征提供因果说明。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Tropical and Subtropical South American Intraseasonal Variability: A Normal-Mode Approach
Instead of using the traditional space-time Fourier analysis of filtered specific atmospheric fields, a normal-mode decomposition method was used to analyze South American intraseasonal variability (ISV). Intraseasonal variability was examined separately in the 30–90-day band, 20–30-day band, and 10–20-day band. The most characteristic structure in the intraseasonal time-scale, in the three bands, was the dipole-like convection between the South Atlantic Convergence Zone (SACZ) and the central-east South America (CESA) region. In the 30–90-day band, the convective and circulation patterns were modulated by the large-scale Madden–Julian oscillation (MJO). In the 20–30-day and 10–20-day bands, the convection structures were primarily controlled by extratropical Rossby wave trains. The normal-mode decomposition of reanalysis data based on 30–90-day, 20–30-day, and 10–20-day ISV showed that the tropospheric circulation and CESA–SACZ convective structure observed over South America were dominated by rotational modes (i.e., Rossby waves, mixed Rossby-gravity waves). A considerable portion of the 30–90-day ISV was also associated with the inertio-gravity (IGW) modes (e.g., Kelvin waves), mainly prevailing during the austral rainy season. The proposed decomposition methodology demonstrated that a realistic circulation can be reproduced, giving a powerful tool for diagnosing and studying the dynamics of waves and the interactions between them in terms of their ability to provide causal accounts of the features seen in observations.
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