摘要
本文利用小波分析方法研究了地球自转日长亚季节近50天和近120天周期变化的时频特征．结果表明，日长近120天周期变化及近50天周期变化的振幅具有明显的年际变化．ENSO事件发生之前，日长近50天周期变化加强，进入ENSO时期，逐渐减弱，成为ENSO产生的先兆之一，同时，日长近120天周期变化显著增强80年代，日长近50天周期变化明显发生了两次周期分岔分岔的一种趋势经历了一个周期延长的过程，收敛于ENSO时期增强的近120天周期变化，该过程不仅与ENSO现象相关联而且可能受到近10年波动的调制作用.同时证实了日长近120天周期变化及近50天周期变化的激发机制主要是同频段的大气环流变化所导致。
A wavelet analysis was applied to study the bine-frequency spectrum of LOD inthe intraseasonal scale including pseudo-50-day, pseudo-120-day oscillations and theatmospheric induced LOD vdriation as well as their correlations with ENSO which isthe most dominant dynamic variation in interannual scale in the system of theatmosphere, oceans and the solid Earth.The space95 LOD data is the combination of modern space geodesy observationssuch as VLBI, SLR, GPS, LLR before 1995. The atmospheric angular momentumdata are from JMA and ECMRWF. The Vondrak band-pass filter was used toeliminate seasonaleffects on intrueasonal variation.The wavelet results suggest that the amplitudes of intraseasonal oscillationsapparently change in interannual scale. Before the ENSO, LOD variation forpseudo-50-day is strong while it becomes weak in ENSO,which seems to be one ofthe precursors to signing the coming ENSO. The LOD variahon for pseudo-120-dayis larger in ENSO than that in La Nino. During the 1980's, the variation forpseudo-50-day of LOD obviously bifurcates twice in period,one strand graduallyundergoes an elongation with a span of about ten years in period convergeing to thestrong pseudo-120-day variation in ENSO, which reveals that the process is not onlywell correlated with ENSO but also seemingly modulated by the decadal scale variation.It is also proved that the atmospheric variation in intraseasonal scale is the mainreason for LOD oscillation in the saxne frequency domain.
出处
《天文学报》
CSCD
北大核心
1998年第1期52-60,共9页
Acta Astronomica Sinica
基金
中科院九五重点资助
