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Ann. Geophys., 23, 753-757, 2005
www.ann-geophys.net/23/753/2005/
© European Geosciences Union 2005
Simultaneous observations of the main trough using GPS imaging and the EISCAT radar
R. W. Meggs1, C. N. Mitchell1, and V. S. C. Howells2
1Department of Electronic and Electrical Engineering, University of Bath, BA2 7AY Bath, UK
2Rutherford-Appleton Laboratory, Chilton, OX11 0QX, UK
Abstract. 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 ExB drift,
the asymmetry (Ia) of equatorial ionization anomaly (EIA), and the
magnetic activity (Kp) 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 ExB drift and Ia. The larger ExB drift
(>20m/s) and smaller |Ia| (<0.3) in summer and
equinoctial months provide a preferable condition to development the ESF.
Conversely, the smaller ExB drift and larger
|Ia| are responsible for the lower ESF occurrence in
winter months. Regarding the effects of magnetic activity, the ESF
occurrence decreases with increasing Kp in the equinoctial and winter months,
but not in the summer months. Furthermore, the larger and smaller
ExB drifts are presented under the quiet
(Kp<3) and disturbed (Kp≥3) conditions, respectively. These results
indicate that the suppression in ESF and the decrease in ExB drifts are mainly caused by the decrease in the eastward
electric field.
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