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 NmF2E; the most probable value NmF2MP; the average monthly median NmF2MED; the arithmetic mean NmF2A; the standard deviations of NmF2 from NmF2E, NmF2MP, and NmF2MED; and the coefficients of variation CVE, CVMP, and CVMED of NmF2 relative to NmF2E, NmF2MP, and NmF2MED, respectively. It follows from the calculations that the CVE, CVMED, and CVMP values vary within the intervals of 12–43%, 12–60%, and 13–75%, respectively, and, in the vast majority of cases, CVE(UT, M) < CVMED(UT, M) and CVE(UT, M) < CVMP(UT, M). If the coefficient CVE in each month of each year is compared for different time points, the lowest CVE value varies from 12% (July) to 19% (December) and occurs during daytime, while the highest CVE 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 NmF2A(UT, M) from NmF2E(UT, M) does not exceed 0.2%.