MJO特征的多尺度子空间重构

Reconstructing the MJO with multiscale window transform

通过构造两种不同类型的理想序列,将多尺度子空间变换(Multiscale Window Transform,MWT)与传统使用最多的带通滤波方法(Butterw orth)进行比较发现:MWT滤波的结果在整体上与原序列几乎完全吻合,而Butterworth的滤波结果在振幅上总是偏小;同时MWT对边界的处理也比Butterworth要好。为此使用这两种方法分别对MJO进行重构,并比较两种方法下MJO特性的差异。结果表明:在经向(meridional)传播上,两种方法得出的MJO基本类似;但在纬向(zonal)传播及其季节变化上,两种方法的结果无论在强度还是分布上都存在明显的差异,并且这种差异主要存在于西太平洋地区。本文发现:MJO波列从年初到夏季由南向北传播,从夏季到岁末传播方向却逆转成由北向南(尤其是在西太平洋地区),这一点与前人的结果迥异。

Recently,a new functional analysis tool was developed,the multiscale window transform（MWT）,to realistically represent and decompose the complex nonlinear multiscale processes within atmospheric and oceanic circulations.In this study,two types of idealized series were constructed to test the effect of the MWT versus the traditional and most widely used band-pass Butterworth filter.It was found that the MWT produced fairly accurate reconstructions,while the Butterworth filter tended to yield series with smaller amplitude.Besides,the boundary effect was successfully suppressed in the MWT reconstructions,in contrast to the Butterworth results.With these observations in mind,we reconstructed the MJO using these two methods.The results showed little difference in the meridional propagation pattern.However,with respect to the zonal distribution,both the strength and propagation patterns were quite different,especially in the western Pacific Ocean.This was particularly significant in terms of the annual mean distribution.It was found that,from January through June,the MJO wave packet propagated northward;but from June through December,the propagation reversed its direction,becoming southward.This propagation reversion is quite different from the scenarios revealed in previous studies.The zonal propagation in the Indian Ocean and Pacific Ocean was different.The results showed that,in the Indian Ocean area,the oscillations in the Northern Hemisphere had a northward trend in spring and summer with the Butterworth filter;while in the case of MWT,the oscillations in spring and summer were less significant than the Butterworth case.In the western Pacific,the zonal propagation of the MJO showed a significant difference between the Butterworth filter and MWT filter.In the Butterworth case,the northward trend of the MJO in the western Pacific Ocean was still evident in summer;while in the case of MWT,the oscillation showed a significant southward trend.It was apparent that the southward trend of zonal propagation was mainly caused by the zonal propagation in the western Pacific Ocean.The MJO distribution was different in all seasons.The strongest oscillation occurred in winter and spring,which,in spring,was obvious in the western Pacific Ocean,whereas in winter it occurred obviously in the Indian Ocean.