Mid-Term Solar Activity Oscillations and Geomagnetic Field Variations

In solar activity, in addition to the 11-year Schwabe cycle, there are also shorter-period oscillations in the range from 27 days to 11 years, which are called mid-term oscillations. In our study, we identify quasi-6-year oscillations in solar activity expressed by the sunspot number SN using wavelet analysis and investigate the characteristics of these variations during 1750-2020. The analysis shows that the similar to 6-year cycle in SN is a real independent oscillation. A similar quasi-6-year periodicity has been found in the monthly mean records of geomagnetic field components at the Sitka and Honolulu observatories during 1910-2020. It was found that the variations of the geomagnetic field in the range of 5-6-year periods can be caused by the effect of variations in solar activity in the same frequency range. In addition, in the SN series and geomagnetic field variations, a quasi-biennial cycle is well observed, the amplitude of which in some time intervals exceeds the amplitude of the cycle with a period of 5-6 years.