Differences in Monthly Medians of foF within Seasons in the Mid-Latitude Ionosphere During the Period of Low Solar Activity in 2007-2008 Years

The paper presents a comparative analysis of diurnal variations in the monthly median critical frequency of the regular ionospheric F layer (foF) for all "standard" seasons during the period of low solar activity in 2007-2008. The hourly data from manual processing of measurements taken at mid-latitude ground-based vertical ionospheric sounding stations Wakkanai (Japan) and Hobart (Australia) located almost symmetrically relative to the geographic equator were analyzed. It is found that the relative differences in the median of the third month of any of the "standard" seasons compared to the median of the second month of the season are significantly higher than the differences in the median of the first month of the season relative to the median of the second month of the season. It is also shown using a specific example of these two mid-latitude stations that, according to their characteristics, the median of November (the last month of the autumn season) corresponds to the beginning of the winter season, and the median of May (the last month of the spring season) - to the beginning of the summer season. It has been established that the relative contribution of solar radiation to changes in the value of the electron concentration at the maximum of the F region (NmF) under conditions of low solar activity in equinoctial seasons, associated with variations in the value and rate of change of the solar zenith angle, is no less than half of the relative contribution to changes in NmF made by variations in the composition of the neutral atmosphere.