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 NmF2_E, the arithmetically average NmF2_A, the standard deviations σ_E(UT,M), and the variation coefficient CV_E(UT,M) of NmF2 relative to NmF2_E, where UT is the universal time. It is found that the value of CV_E(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 CV_E(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.