VHF radar studies of counter electrojet events during the northern winter solstice period of 1992

Abstract

Abstract A sequence of counter electrojet events during the winter solstice period of 1992 are studied along with control quiet day observations at the magnetic equatorial location of Trivandrum (8.5°N, 76.5°E; dip 0.5°N) using VHF (54.95 MHz) coherent backscatter radar observations. Some of the unusual features observed on these days are: (1) an unusual radar signal with reversed Doppler values corresponding to westward electric field, for a brief duration of 5 min at approximately 1330 h, at the higher altitudes 112–117 km on 21 January 1992, as against the usual observation of the signal at lower altitudes below 112 km during CEJ times; (2) type I plasma waves in the late afternoon around 1800 h (after the CEJ event) at altitudes above 101 km (on 21 and 23 January 1992) when the backscattered power is low, indicating the unusual tidal influences on the electric field behavior on certain CEJ days; (3) distortions in the height structure of the vertical polarization electric field, attributed to the modulation of the electrojet altitude structure by action of zonal neutral winds; (4) westward electric field, as seen by the radar, even while the ΔH values are positive.