The effects of the pre-reversal drift, the EIA asymmetry, and magnetic activity on the equatorial spread F during solar maximum

We use a digisonde at Jicamarca and a chain of GPS receivers on the west side of South America to investigate the effects of the pre-reversal enhancement (PRE) in E × B drift, the asymmetry (I_a) of equatorial ionization anomaly (EIA), and the magnetic activity (K_p) on the generation of equatorial spread F (ESF). Results show that the ESF appears frequently in summer (November, December, January, and February) and equinoctial (March, April, September, and October) months, but rarely in winter (May, June, July, and August) months. The seasonal variation in the ESF is associated with those in the PRE E × B drift and I_a. The larger E × B drift (>20m/s) and smaller /I_a/ (<0.3) in summer and equinoctial months provide a preferable condition to development the ESF. Conversely, the smaller E × B drift and larger / I_a/ are responsible for the lower ESF occurrence in winter months. Regarding the effects of magnetic activity, the ESF occurrence decreases with increasing K_p in the equinoctial and winter months, but not in the summer months. Furthermore, the larger and smaller E × B drifts are presented under the quiet (K_p < 3) and disturbed (K_p≥3) conditions, respectively. These results indicate that the suppression in ESF and the decrease in E × B drifts are mainly caused by the decrease in the eastward electric field.