Structural changes in the tidal components in mesospheric winds as observed by the MF radar during afternoon counter electrojet events

Abstract

In this paper we examine the relationship between the tidal characteristics as observed by the MF radar at Tirunelveli (8.7°N, 77.8°E, geographic; 0.3°N magnetic dip) and the occurrence of afternoon counter electrojet (ACEJ) events. A reduction in the diurnal tide activity and/or an enhancement of semi-diurnal tide amplitude is observed on many of the ACEJ days. A clear anticorrelation is seen between the afternoon electrojet strength and the amplitude of the semi-diurnal tide in the solstitial months of June and July, 1995. The results presented herein provide observational support to the earlier numerical models that consider the interplay of various tidal modes in the evolution of equatorial ionospheric current system whose extreme manifestation in ground-geomagnetic field variations being the reversal of the electrojet in the afternoon hours.