Geomagnetizm i aèronomiâ, Vol 63, No 4 (2023)

The study of diurnal variations of the statistical characteristics of the day-to-day variability of the
NmF2 electron number density of the F2 ionosphere layer for each month (M) of the year in geomagnetically
quiet conditions at low solar activity according to hourly measurements of the critical frequency of the F2 ionosphere
layer was carried out in Huancayo and Jicamarca. We calculated the NmF2E mathematical expectation,
the NmF2A arithmetic mean, the most probable NmF2MP, the NmF2MED arithmetic mean monthly
median, standard deviations σE, σA, σMP, and σMED and coefficients of variations CVE, CVA, CVMP, and
CVMED of the NmF2 value from NmF2E, NmF2A, NmF2MP, and NmF2MED, respectively. It has been found
that the difference of NmF2MED(UT,M) from NmF2E(UT,M) does not exceed 46%, NmF2MP(UT,M) from
NmF2E(UT,M): 102% and NmF2MP(UT,M) from NmF2MED(UT,M): 85%, where UT is Universal Time.
The calculated statistical parameters σE, σA, σMP, σMED, CVE, CVA, CVMP, and CVMED are the characteristics
of the NmF2 variability from one day to another day at fixed M and UT values over low-latitude Huancayo
and Jicamarca ionosondes in geomagnetically quiet conditions at low solar activity. The calculations showed
that the CVE, CVMED, and CVMP coefficients vary between 18%–82%, 19%–107%, and 18%–288%, respectively,
and in the majority of cases, CVE(UT,M) is less than CVMED (UT,M) and CVMP(UT,M). It was shown
that minimizing the standard deviation and the variation coefficient of NmF2 using the mathematical expectation
of NmF2 provides the best description of the set of NmF2 measurements with one single NmF2 statistical
parameter under the considered conditions. The lowest CVE varies from 18% (April) to 29% (September)
and the highest CVE ranges from 63% (November) to 73% (January). The average CVE value (average relative
day-to-day variability of NmF2) is highest in September (40%) and lowest in April (33%).