Diurnal Variations in the Statistical Characteristics of the Variability of the Midlatitude NmF2 during Quiet Geomagnetic Conditions at Low Solar Activity

Abstract

The work examines diurnal variations in the statistical characteristics of the variability of the electron number density NmF2 of the maximum of the ionspheric F2 layer during quiet geomagnetic conditions at low solar activity based on hourly ionosonde measurements of the critical frequency of the ionspheric F2 layer from 1957 to 2017 over Moscow. The statistical parameters of NmF2 are calculated for each month M of each year at the universal time UT = 0, 1, … 23 h: the mathematical expectation NmF2_E; the most probable value NmF2_MP; the average monthly median NmF2_MED; the arithmetic mean NmF2_A; the standard deviations of NmF2 from NmF2_E, NmF2_MP, and NmF2_MED; and the coefficients of variation CV_E, CV_MP, and CV_MED of NmF2 relative to NmF2_E, NmF2_MP, and NmF2_MED, respectively. It follows from the calculations that the CV_E, CV_MED, and CV_MP values vary within the intervals of 12–43%, 12–60%, and 13–75%, respectively, and, in the vast majority of cases, CV_E(UT, M) < CV_MED(UT, M) and CV_E(UT, M) < CV_MP(UT, M). If the coefficient CV_E in each month of each year is compared for different time points, the lowest CV_E value varies from 12% (July) to 19% (December) and occurs during daytime, while the highest CV_E value lies in the interval from 26% (June) to 43% (December). For each UT, the lowest and highest values of this coefficient in the autumn, winter, and spring months are greater than those for the summer months. It was found that the difference of NmF2_A(UT, M) from NmF2_E(UT, M) does not exceed 0.2%.