Stochastic and oscillatory forcing of global atmospheric angular momentum
Stochastic and oscillatory forcing of global atmospheric angular momentum
复制标题
全球大气角动量的随机和振荡强迫
DOI：
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
C. Penland
中科院分区：
文献类型：
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作者：
K. Weickmann;W. Robinson;C. Penland
利用全球大气角动量（AAM）观测统计资料和全球大气力矩的三分量马尔可夫模型，研究了全球大气角动量的时间变化和强迫。该模型由山体（τM）和摩擦（τ *F）力矩的随机强迫以及摩擦力矩对AAM的普遍负反馈组成。AAM异常在30天的时间尺度上被阻尼，并受到具有1.5天（τM）和6天（τ *F）去相关时间尺度的扭矩的影响。AAM、τM和τF的大部分季节内方差和协方差都是由马尔可夫模型来解释的。在10至90天的波段内，模型协方差和观测协方差之间的差异最大，当使用未按季节分层的数据时，差异占方差的10-30%。一个特别突出的偏离马尔可夫模型是振荡强迫AAM的摩擦扭矩在30至60天的周期。此外，在整个10- 90天的时间段内，τF和τM之间存在较大的相干方差，摩擦扭矩领先于山脉扭矩。全局转矩之间的这种“反馈”是由马尔可夫模型中没有表示的物理过程引起的。本文描述了随机山脉力矩、摩擦力矩和振荡型马登-朱利安振荡的天气学特征。
The temporal variability and forcing of global atmospheric angular momentum (AAM) is studied using a three-component Markov model derived from observed statistics of global AAM and the global torques. The model consists of stochastic forcing by the mountain (τM) and friction (τ *F) torque plus a pervasive negative feedback on AAM by the friction torque. AAM anomalies are damped at a 30-day timescale and forced by torques having 1.5-day ( τM) and 6-day (τ *F) decorrelation timescales. A large portion of the intraseasonal variance and covariance of AAM, τM, and τF is accounted for by the Markov model. Differences between the modeled and the observed covariances are maximized in the 10- to 90-day band and account for 10–30% of the variance when using data not stratified by season. An especially prominent deviation from the Markov model is the oscillatory forcing of AAM by the frictional torque at 30- to 60-day periods. Additionally, there is greater coherent variance between τF and τM across the entire 10- to 90-day band, with the frictional torque leading the mountain torque. This “feedback” between the global torques results from physical processes not represented in the Markov model. The synoptic characteristics of the stochastic mountain and frictional torques and of the oscillatory Madden-Julian Oscillation are described.