Solar-Activity Indices for the Ionosphere in Cycles 23 and 24: the Form of Cycles

Analysis of the features of the form of low solar cycles 23 and 24 for the solar-activity indices ( F is the solar radio flux at a wavelength of 10.7 cm, Rz and Ri are the relative numbers of sunspots, old and new versions) and the ionospheric index of this activity T . For this, the analyzed indices are reduced to the Rz scale and smoothed (with a 24-month Gaussian filter) values of these indices are considered. It was found that the cycle forms were preserved for cycles 23 and 24 and previous solar cycles by index Rz , i.e., a definite connection was made between the cycle amplitude and the time of the onset of the cycle maximum. The same relationship was observed for the Ri index, except for cycle 23, in which the observed cycle maximum occurred 7 months later than the expected time based on previous cycles. For indices F and T , the cycle shapes also persisted up to cycle 22, but the observed cycle maxima in cycles 23 and 24 occurred almost a year later than expected, which is one of the properties of the new regime of prolonged low solar activity. In this mode, the connection between the Ri and F indices is broken, which leads to different cycle forms for these indices.