Energy Spectrum Characteristics of Boreal Summer Intraseasonal Oscillations: Climatology and Variations during the ENSO Developing and Decaying Phases
Energy Spectrum Characteristics of Boreal Summer Intraseasonal Oscillations: Climatology and Variations during the ENSO Developing and Decaying Phases
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DOI：
10.1175/2008jcli2331.1
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发表时间：
2008-12
影响因子：
4.9
通讯作者：
Ailan Lin;Tim Li
中科院分区：
文献类型：
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作者：
Ailan Lin;Tim Li
利用25年（1979- 2003）的观测资料，分析了印度西太平洋地区夏季季节内振荡（BSISO; 5 - 10月）能量谱的地理相关特征。BSISO能谱分布具有明显的区域特征。在赤道（5°S-5°N），静止模和向东传播模最明显，而在非赤道区（10°-20 ° N），向西传播模占主导地位。向东的季节内振荡（ISO）谱集中在30-60天周期和纬向波数1上，而向西的模态则覆盖了更宽的空间（波数）和时间（周期）范围。沿着阿拉伯海、孟加拉湾和南海（SCS）纬度，在30-60天（10-20天）周期内，波数1的主导模式是向东（向西）传播;对于纬向波数2，在30-60天和10-20天周期内，波数1的主导模式都是向西传播。与纬向和纬向模态能量谱的绝对振幅相比，北向传播是印度西太平洋地区北半球夏季最主要的模态。最强的北向传播BSISO信号出现在热带印度洋东部。在厄尔尼诺和拉尼娜的发展和衰减阶段，BSISO的变化有显著差异。在El Nino（La Nina）发展的夏季，赤道向东传播增强（减弱），西太平洋（140°E以东）向北传播增强（减弱）。在ElNino（LaNina）衰减的夏季，赤道向东传播减弱（增强），而发展的夏季相反，赤道向西传播和南海及西太平洋向北传播受到抑制（增强）。衰减夏季的BSISO变化幅度大于发展夏季。BSISO变化的这种不对称性主要归因于ENSO发展和衰减阶段背景平均气流变化的不对称性。
The geographic-dependence characteristics of the energy spectrum of the boreal summer intraseasonal oscillation (BSISO; May–October) over the Indo–western Pacific region were analyzed using 25-yr (1979– 2003) observational data. The BSISO energy spectrum distribution exhibits a distinctive regional characteristic. The stationary and eastward-propagating modes are most pronounced at the equator (5°S–5°N), while the westward-propagating modes are dominant in the off-equatorial region (10°–20°N). While the eastward intraseasonal oscillation (ISO) spectrum agglomerates on the 30–60-day period and zonal wavenumber 1, the westward mode covers wider spatial (wavenumber) and temporal (period) range. Along the Arabian Sea, Bay of Bengal, and South China Sea (SCS) latitudes, the dominant wavenumber 1 mode is the eastward (westward) propagation at the 30–60-day (10–20 day) period; for zonal wavenumber 2, the dominant mode is the westward propagation at both the 30–60-day and 10–20-day periods. Compared to the absolute amplitude of both zonal and meridional mode energy spectrum, northward propagation is the most predominant mode in boreal summer over the Indo–western Pacific regions. The strongest northwardpropagating BSISO signal appears in the eastern tropical Indian Ocean. The variation of BSISO differs significantly in the El Nino and La Nina developing and decaying phases. During the El Nino (La Nina) developing summer, the eastward propagation is enhanced (weakened) at the equator, while the northward propagation is also strengthened (weakened) over the western Pacific (east of 140°E). During the El Nino (La Nina) decaying summer, the eastward propagation weakens (strengthens) at the equator, opposite to that in the developing summer; the westward propagation off the equator and the northward propagation over SCS and the western Pacific are suppressed (enhanced). The amplitude of the BSISO variation is stronger in the decaying summer than that in the developing summer. This asymmetry in BSISO variations is primarily attributed to the asymmetry of the background mean flow change associated with the developing and decaying phases of ENSO.