Dependence of the F2-layer critical frequency median at midlatitudes on geomagnetic activity

Abstract

We put forward a method of separating the geomagnetic activity contribution to the F2-layer critical frequency median, foF2med, at middle latitudes. It is based on the analysis of foF2, which is the ratio foF2med/foF2q in percent, where foF2q is the F2-layer critical frequency for quiet conditions. The quantities foF2q and foF2 depend on solar and geomagnetic activity respectively. These dependences are taken into account using indices F12 (annual average solar radio emission flux at 10.7 cm) and Apm (monthly average Ap index), thus facilitating the use of this method for forecasting foF2med. With this method, from Slough station (51.5° N, 0.6° W) data for midday and midnight for 1954 to 1995 we have found that at midnight the foF2 dependence on Apm is significant at the 95 % confidence level for equinoxes and summer. For midday, this dependence is less pronounced and is significant only from April to July. At equinoxes and summer, an Apm increase causes a foF2 decrease. For midnight, this feature is more pronounced than for midday. This regularity is also valid for annual average Apm and foF2