Disturbances in the Ionospheric F2 Region Associated with Geomagnetic Storms II. Middle Latitudes

Abstract

An attempt is made to account for the F2 disturbances in middle latitudes associated with the geomagnetic storms in term of the vertical drift of the electron. For this purpose, at first it is shown that in middle latitudes the variations of foF2 on the storm day are classified in two types, negative and positive disturbances, the former of which is the same as the representative variation in high latitudes while the latter the analogous to the variation in low latitudes (including the equator), on the other hand, the variations of h'F2 are analogous to those in high and low latitudes, regardless of the seasons.The vertical drift of the electron is considered to be caused by an electric field deduced from the disturbance-daily variation of the geomagnetic field. The results of the calculations for individual states show that two types of disturbances in middle latitudes seem to be explained as an effect of the vertical drift of the electron, though the coincidence between the observed and calculated for the positive type is not sufficient. From the above results, together with the results previously obtained for the equatorial zone, it is found that the occurrence of the positive or negative disturbances is ascribed to the conditions that the phase of the drift velocity of the electron on the quiet day is the same as that of the drift velocity on the disturbed day (negative) or the phase of the former differs from that of the latter by about 180° (positive). It is also found that the seasonal and latitudinal variations of the F2 disturbance are due to the existence of the Sq dynamo current in the ionosphere.