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arXiv 1605.04005physics.space-ph
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基于小波变换的日地耦合研究

A Wavelet Based Approach to Solar--Terrestrial Coupling

Ch. Katsavrias, A. Hillaris, P. Preka--Papadema

摘要:

瞬时和周期性的太阳活动驱动地磁扰动;这些都是量化的DST,AE指数时间序列(除其他外)。瞬变扰动与行星际日冕物质抛射(ICME)有关,而周期性扰动与共转相互作用区(CIR)有关。我们研究了第23太阳周内地磁扰动与太阳风驱动因子的关系,其中驱动因子用ICME和CIR发生率表示,并与DST和AE进行了比较:首先,使用连续小波变换(CWT)检测地磁扰动和太阳风驱动因子中具有共同周期性的项。然后,分别从互小波谱(XWT)和小波相干性(WTC)计算这些周期项的公共功率和相位相干性。在27天的时间尺度上,我们的结果表明ICME和CIR对地磁扰动的影响是反相关的。前者在太阳活动极大期调制DST和AE时间序列,后者在太阳活动减少期间调制。这些调制的相位关系高度非线性。只有ICME的年频率分量与DST和AE锁相。在大约1.3-1.7年的时间尺度上,CIR似乎是整个太阳活动周23的地磁指数的主要驱动力。

英文摘要:

Transient and recurrent solar activity drive geomagnetic disturbances; these are quantified (amongst others) by DST, AE indices time-series. Transient disturbances are related to the Interplanetary Coronal Mass Ejections (ICMEs) while recurrent disturbances are related to corotating interaction regions (CIR). We study the relationship of the geomagnetic disturbances to the solar wind drivers within solar Cycle 23 where the drivers are represented by ICMEs and CIRs occurrence rate and compared to the DST and AE as follows: terms with common periodicity in both the geomagnetic disturbances and the solar drivers are, firstly, detected using continuous wavelet transform (CWT). Then, common power and phase coherence of these periodic terms are calculated from the cross-wavelet spectra (XWT) and waveletcoherence (WTC) respectively. In time-scales of about 27 days our results indicate an anti-correlation of the effects of ICMEs and CIRs on the geomagnetic disturbances. The former modulates the DST and AE time series during the cycle maximum the latter during periods of reduced solar activity. The phase relationship of these modulation is highly non-linear. Only the annual frequency component of the ICMEs is phase-locked with DST and AE. In time-scales of about 1.3-1.7 years the CIR seem to be the dominant driver for both geomagnetic indices throughout the whole solar cycle 23.

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