Lower E-region echoes over the magnetic equator as observed by the MF radar at Tirunelveli (8.7° N, 77.8° E) and their relationship to E_sq and E_sb

Abstract. The spaced antenna medium frequency (MF) radar at Tirunelveli (8.7° N, 77.8° E, geographic; 1.7° N, magnetic dip), the only one of its kind currently operating close to the magnetic equator, has provided an opportunity to investigate the electrodynamical processes related to the equatorial electrojet (EEJ) and their influence on the radar scatterers at medium frequencies in the lower E-region heights (90–98 km). Making use of the full correlation analysis that enables determination of useful geometrical parameters from the ground diffraction pattern, the present work delineates for the first time the characteristics of the radar scatterers during the occurrences of equatorial sporadic E (E_sq) and blanketing sporadic E (E_sb) noticed in simultaneous ionospheric sounding records at Tirunelveli. The ground magnetometer data provide indirect information on the strength of the EEJ and afternoon reverse EEJ or counterelectrojet (CEJ). The results presented in this work also reveal the height dependence of the radar echo intensity and some of the geometrical parameters at certain times, thus clearly bringing out the complex interplay of various physical processes in the probing region.