Simultaneous observations of the main trough using GPS imaging and the EISCAT radar

摘要

We use a digisonde at Jicamarca and a chain of GPSreceivers on the west side of South America to investigate the effects ofthe pre-reversal enhancement (PRE) in ExB drift,the asymmetry (I_a) of equatorial ionization anomaly (EIA), and themagnetic activity (K_p) on the generation of equatorial spread F (ESF). Resultsshow 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 seasonalvariation in the ESF is associated with those in the PRE ExB drift and I_a. The larger ExB drift(>20m/s) and smaller |I_a| (<0.3) in summer andequinoctial months provide a preferable condition to development the ESF.Conversely, the smaller ExB drift and larger|I_a| are responsible for the lower ESF occurrence inwinter months. Regarding the effects of magnetic activity, the ESFoccurrence decreases with increasing K_p in the equinoctial and winter months,but not in the summer months. Furthermore, the larger and smallerExB drifts are presented under the quiet(K_p<3) and disturbed (K_p≥3) conditions, respectively. These resultsindicate that the suppression in ESF and the decrease in ExB drifts are mainly caused by the decrease in the eastwardelectric field.