Impact of the Solar Activity Variations on the Low-Latitude Day-to-Day Variability of NmF2 During Geomagnetically Quiet Conditions Obtained from the Huancayo and Jicamarca Ionosonde Observations

The statistical characteristics of the day-to-day variability of the F2-layer peak electron number density, NmF2, measured by the low-latitude Huancayo and Jicamarca ionosondes are studied for each month, M, in a year for geomagnetically quiet conditions at low and moderate solar activity during the time period from 1957 to 2022. The NmF2 statistical parameters under study are the mathematical expectation NmF2E, the arithmetically average NmF2A, the standard deviations sigma E(UT,M), and the variation coefficient CVE(UT,M) of NmF2 relative to NmF2E, where UT is the universal time. It is found that the value of CVE(UT,M) that determines the relative day-to-day variability of NmF2 is changed in the intervals of 15-68% and 14-68% for the low and moderate solar activity conditions, respectively. The comparison of CVE(UT,M) for the low and moderate solar activity conditions under consideration shows for the first time that the increase in the solar activity level increases or decreases the relative day-to-day NmF2 variability in the range from - 24 to 15%. In the vast majority of cases the considered increase in the solar activity level decreases the relative day-to-day NmF2 variability while the longest periods of the corresponding increase in the relative day-to-day NmF2 variability occur in April.