NmF2 Variability at Different Longitudes in Mid-Latitudes: The Role of Geomagnetic Activity

Based on data from mid-latitude ionospheric stations at close corrected geomagnetic latitudes, the properties of the variability in the F2 layer peak density (NmF2) at different longitudes were analyzed during increased (48 > ap(τ) > 27) and high (ap(τ) > 48) geomagnetic activity, where ap(τ) is the weighted average ap-index of this activity. The standard deviation σ of Nm fluctuations with respect to the quiet level and the average shift of these fluctuations x_ave were used as characteristics of this variability. It was found that at all analyzed stations, the variance σ ² for increased geomagnetic activity is greater than for quiet conditions but hardly differs from σ ² for high geomagnetic activity. For all analyzed cases, the average shift x_ave < 0, and for high geomagnetic activity, the absolute value of x_ave is greater than for increased geomagnetic activity. The difference in x_ave values between the analyzed stations is quite large. One reason for this difference may be related to the dependence of x_ave on geomagnetic latitudes. Approximations of the geomagnetic field by the tilted dipole (TD), eccentric dipole (ED), or using corrected geomagnetic (CGM) coordinates were used to select these latitudes. It was found that the dependence of x_ave on ED latitude is more accurate than the dependence of x_ave on TD latitude and, moreover, the dependence of x_ave on CGM latitude. Therefore, ED latitudes, and not CGM latitudes, are optimal for accounting for storm effects on the F2 layer peak density at mid-latitudes. This conclusion has apparently been obtained for the first time.