Properties of the Variability of the Maximum Density of the F 2-Layer over Almaty at Different Levels of Solar and Geomagnetic Activity

The properties of the variability of the maximum density of the F 2-layer Nm at different levels of solar and geomagnetic activity have been analyzed based on hourly data of the Almaty station (43.2(degrees)N, 104(degrees) E) for 1958-1988. The standard deviation sigma(x) of the fluctuations of Nm relative to the quiet level (x = (Nm/Nm(0) - 1) x 100, %) and the average shift of these fluctuations x(ave) are used to characterize this variability. In this path, an empirical model of the F 2-layer maximum density Nm(0 )for low geomagnetic activity has been created. It has been found that the variability of Nm depends weakly on the level of solar activity. The dependence of the variability of Nm on geomagnetic activity is one of the main ones, along with the dependences of this variability on time of day and season. In general, the variance sigma(2)(x) is smaller for quiet conditions than for periods of high geomagnetic activity. However, during periods of high geomagnetic activity, a further increase in geomagnetic activity does not lead to an increase in the variance sigma(2)(x). The saturation in the increase in the variance sigma(2)(x) against the background at a continuing increase in geomagnetic activity and the absence of this saturation for the average shift x(ave) seems to be a stable property of the variability of the mid-latitude ionosphere during periods of geomagnetic storms. This conclusion is based on an additional analysis of ionospheric variability according to data from the Irkutsk and Yamagawa stations, which are located about 10 degrees north and south of Almaty station, respectively.