Quasi-periodicities and Empirical Modes of the Heliospheric Magnetic Field

Quasi-periodicities in solar phenomena including variations in the heliospheric magnetic field have attracted attention in the past. Recently, such a periodicity near 140- 150 days has been of interest. In a recent analysis of solar cycle variations in the Sun's open magnetic flux, we found a quasi-periodicity of approximately one and one-half years in the radial component and the field magnitude that persists during the last four sunspot cycles. Inspection of the data revealed that this signal was variable in both amplitude and period. Power spectra having proved marginally useful in revealing the signal properties, we apply a new technique called Empirical Mode Decomposition (Huang et al., 1998) that treats both the frequency and amplitude as time-dependent. Application of this technique revealed several quasi-periodic modes including the mode near 1 and 1/2 years and the mode near 140 days that was not evident by inspection alone. The results of this analysis will be presented and the origin of the several periodicities will be discussed. Reference: Huang, N. E. Z. Shen, S. R. Long, M. C. Wu, H. H. Shih, Q. Zheng, N.-C. Yen, C. C. Tung, and H. H. Liu, Proc. R. Soc. Lond., A 454, 903-995, 1998.