Midday reversal of equatorial ionospheric electric field

R G Rastogi

doi:10.1007/s005850050547

Abstract

A comparative study of the geomagnetic and ionospheric data at equatorial and low-latitude stations in India over the 20 year period 1956â1975 is described. The reversal of the electric field in the ionosphere over the magnetic equator during the midday hours indicated by the disappearance of the equatorial sporadic E region echoes on the ionograms is a rare phenomenon occurring on about 1% of time. Most of these events are associated with geomagnetically active periods. By comparing the simultaneous geomagnetic H field at Kodaikanal and at Alibag during the geomagnetic storms it is shown that ring current decreases are observed at both stations. However, an additional westward electric field is superimposed in the ionosphere during the main phase of the storm which can be strong enough to temporarily reverse the normally eastward electric field in the dayside ionosphere. It is suggested that these electric fields associated with the VÃBz electric fields originate at the magnetopause due to the interaction of the solar wind and the interplanetary magnetic field.

Highlights

The establishment of geomagnetic and ionospheric observatories at low magnetic latitudes in Peru and Columbia during IGY-IGC period have provided very valuable data on the equatorial electrojet and equatorial ionosphere. Knecht and McDue (1962) have described the special properties of the equatorial sporadic E layer, is-q, which was shown to be closely related to the equatorial electrojet both in daily and latitudinal variations.Bartels and Johnston (1970a, b) had shown that the geomagnetic horizontal ®eld, r , at Huancayo during the daytime hours on certain occasions decrease below the corresponding nighttime base value. Gouin and Mayaud (1967) called such events counter electrojets and suggested they may be due to a westward current in the equatorial ionosphere. Rastogi et al (1971) showed, for the ®rst time, that the counter electrojet events observed in geomagnetic r ®eld, the absence of is-q reections in the ionograms and the reversal of the ionospheric drift direction during the daytime hours at an equatorial station were concurrent phenomena
Rastogi et al (1971) showed, for the ®rst time, that the counter electrojet events observed in geomagnetic r ®eld, the absence of is-q reections in the ionograms and the reversal of the ionospheric drift direction during the daytime hours at an equatorial station were concurrent phenomena
Comparing the high resolution modi®ed range time intensity (MRTI) records of VHF backscatter radar echoes at Jicamarca and the magnetograms at Huancayo and Fuquene, Rastogi et al (1977) showed that the E region irregularities disappear precisely when Dr at Huancayo minus Dr at Fuquene decreases below the corresponding night time value

Summary

Introduction

The establishment of geomagnetic and ionospheric observatories at low magnetic latitudes in Peru and Columbia during IGY-IGC period have provided very valuable data on the equatorial electrojet and equatorial ionosphere. Knecht and McDue (1962) have described the special properties of the equatorial sporadic E layer, is-q, which was shown to be closely related to the equatorial electrojet both in daily and latitudinal variations.Bartels and Johnston (1970a, b) had shown that the geomagnetic horizontal ®eld, r , at Huancayo during the daytime hours on certain occasions decrease below the corresponding nighttime base value. Gouin and Mayaud (1967) called such events counter electrojets and suggested they may be due to a westward current in the equatorial ionosphere. Rastogi et al (1971) showed, for the ®rst time, that the counter electrojet events observed in geomagnetic r ®eld, the absence of is-q reections in the ionograms and the reversal of the ionospheric drift direction during the daytime hours at an equatorial station were concurrent phenomena. Rastogi et al (1971) showed, for the ®rst time, that the counter electrojet events observed in geomagnetic r ®eld, the absence of is-q reections in the ionograms and the reversal of the ionospheric drift direction during the daytime hours at an equatorial station were concurrent phenomena.

Results

Conclusion