Time changes of solar activity, interplanetary magnetic field and solar wind velocity at the Earth's orbit in different spectral bands

We present the results of our analysis of the spectra of the interplanetary magnetic field (IMF) and the solar wind velocity (V) calculated on the basis of measurements near the Earth's orbit for the period 1964-1997, and of the sunspot number W. The major aim is to search for similar features in various frequency bands, with an emphasis on the T similar to 11 yr period of solar (sunspot) cycle and its harmonics, and on so-called "intermittent" oscillations at periods T similar to 1.3yr and T similar to 150 d. We also extract trends from the data to determine long-period changes of I M F and V. A method of non-linear spectral analysis, which we term "the method of global minimum" (MGM) is used. MGM allows self-consistent identification of trends from data and nonstationary sinusoids and estimation of statistical significance of spectral components. The IMF and W spectra both show the main solar cycle at T = 10.8 yr. In addition, the spectrum of the IMF includes (at 99.8% confidence levels) harmonics of this cycle with periods of 151.3 and 136.5d. We also detect nonstationary sinusoids at T = 1.3 yr in the spectra of IMF and of V and describe their parameters. The detailed description of the 1.3-yr oscillations in the solar wind is of particular interest in that the oscillations are likely to be connected to variations in the rotation rate with the same period near the base of convection zone of the Sun discovered in SOHO data. The 1.3-yr oscillations are not present in the W spectra. Instead, we find oscillations at T = 1.014 and 0.950 yr and suggest an explanation of their presence. Relation between the variations in the spectra of W and V is not as evident as between W and the IMF, however, it exists. In particular, harmonics of the 10.8-yr solar cycle (e.g., sinusoid at T = 261.7 d) are present in the spectrum of V. Components in the spectra described by high-amplitude sinusoids with T = 198 5 yr in the IMF spectrum and with T = 54 4 yr in the V spectrum make contributions to the long-term trends in these parameters. The trend of V demonstrates a 55% increase in the solar wind velocity for the period 1964-1997. The IMF trend shows a 45% increase of the IMF magnitude for the same time interval; extrapolation of this temporal variation to the past leads to a doubling of the IMF value during the last 100 yr. (C) 2007 Elsevier Ltd. All rights reserved.