抚仙湖太阳观测和研究基地知识库

The daily interplanetary magnetic field (IMF) Bx, By, and Bz components from 1967 January 1 to 2018 December 31 listed in the OMNI database are used to investigate their periodicity and study temporal variation of their rotation cycle lengths through continuous wavelet transform, autocorrelation, and cross-correlation analyses. The dominant rotation period in each of the daily Bx, By, and Bz components is 27.4 days, implying the existence of rotational modulation in the three time series. The dependence of the rotation cycle lengths for both Bx and By components on solar cycle phase almost shows the same result. The rotation cycle lengths for both Bx and By components increase from the start to the first year of a new Schwabe cycle, then decrease gradually from the first to the fourth year, and finally fluctuate around the 27.4-day period within a small amplitude from the fourth year to the end of the Schwabe solar cycle. For the Bz component, its rotation cycle length does not show such a solar cycle variation. The significant periods in the variation of Bx rotation are 2.9, 3.4, 4.3, 4.9, 10.5, and 11.9 yr, and there exist significant periods of 3.4, 9.9, and 14.1 yr in the variation of By rotation. The relationship of solar activity with Bx and By components is complex. The possible mechanisms for the temporal variation of the rotation period of the three components are discussed.