Evolutionary Characteristics of the Interplanetary Magnetic Field Intensity

Abstract

Abstract We use several mathematical methods, such as the continuous wavelet transform, the wavelet coherence (WTC), and the partial wavelet coherence, to investigate the distribution and oscillation periods of the daily interplanetary magnetic field (IMF) intensity as well as the connection between IMF fluctuations and solar activity indices (the magnetic plage strength index and the Mount Wilson sunspot index). The daily IMF intensity generally approximately follows a log-normal distribution that is directly related to the distribution of the active region flux. The short-term periods of the IMF are about 13.7, 27.6, 37.1, and 75.3 days. They are driven by the quasi-periodicity of the magnetic surges on the solar surface. The medium-term periods of 1.07 and 1.82 years need to be derived from the stochastic interaction of local fields and meridional flows, since coronal holes reflect the transport of the magnetic flux on the solar surface and variations in the meridional flow are seen in the heliosphere. The 10.9-year period is the Schwabe solar cycle and is to be mentioned first. The solar cycle variation of the IMF is not thought to be related to weak solar magnetic activity, but is dominated by the strong solar magnetic field activity seen on the disk, because the footpoints of the time-varying component of the interplanetary magnetic flux are rooted in regions that are located near the sources of coronal mass ejections that are related to active regions, while the constant component in the IMF is thought to initially and mainly come from the weak solar magnetic field activity. Finally, the slow variation of the IMF indicates that it may have a period of longer than 50 years.