Extratropical aspects of the 40–50 day oscillation in length-of-day and atmospheric angular momentum
Extratropical aspects of the 40–50 day oscillation in length-of-day and atmospheric angular momentum
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DOI：
10.1029/91jd02339
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发表时间：
1991-12
影响因子：
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通讯作者：
J. Dickey;M. Ghil;S. Marcus
中科院分区：
文献类型：
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作者：
J. Dickey;M. Ghil;S. Marcus
在2年或更短的时间尺度上，地球自转的波动主要受大气影响;对日长（LOD）和大气角动量（AAM）数据的光谱分析表明，40-50天波段的变化显著增加。在40-50天时间尺度上的LOD和AAM波动以前被认为与Madden和Julian（1971）（以下简称MJ）首次描述的热带对流驱动波有关。然而，在全球大气3年（1120天）永久1月模拟的AAM中，也发现了一个以42天为中心的显著谱峰，该模拟使用了加州大学洛杉矶分校（UCLA）的一个版本的大气环流模式（GCM），该模式不会引起热带地区的MJ振荡。在目前的工作中，40-50天振荡的研究使用两个记录之间的12年重叠：（1）AAM数据，从国家气象中心（NMC）编制的;（2）LOD变化从喷气推进实验室卡尔曼滤波地球自转序列。根据UCLA GCM的结果，我们分析了不同纬度带的NMC记录，以确定中纬度和热带AAM振荡的可能不同的来源。结果表明，两个季节内振荡存在于地气系统：热带，50天的振荡与对流驱动的MJ波和中纬度，40天的振荡与非纬向流与地形的相互作用。
Fluctuations in Earth rotation over time scales of 2 years or less are dominated by atmospheric effects; spectral analyses of length-of-day (LOD) and atmospheric angular momentum (AAM) data show significantly increased variability in the 40–50 day band. LOD and AAM fluctuations on the 40–50 day time scale have previously been linked to tropical, convectively driven waves of the type first described by Madden and Julian (1971) (referred to as MJ hereinafter). A significant spectral peak centered at 42 days has also been found, however, in the AAM of a 3-year (1120-day) perpetual-January simulation of the global atmosphere, performed using a version of the University of California at Los Angeles (UCLA) general circulation model (GCM) which does not give rise to MJ oscillations in the tropics. In the present work the 40–50 day oscillation is studied using the 12-year overlap between two records: (1) AAM data, compiled from the National Meteorological Center (NMC); and (2) LOD variation from the Jet Propulsion Laboratory Kalman-filtered Earth rotation series. We analyze the NMC records by latitude belts, in light of the UCLA GCM results, in order to identify possibly distinct sources of the AAM oscillation in the mid-latitudes and the tropics. Results suggest that two intraseasonal oscillations exist in the Earth-atmosphere system: a tropical, 50-day oscillation associated with the convectively driven MJ wave and a mid-latitude, 40-day oscillation associated with the interaction of nonzonal flow with topography.