First Multi‐Beam Radar Studies of F Region Irregularities Beyond the Equatorial Ionization Crest Using the Haringhata Radar in India

This paper presents the first multi‐beam radar observations of the F region field‐aligned irregularities (FAIs) made using a recently established high power 53 MHz radar at Haringhata (22.93°N, 88.5°E, geomagnetic latitude 19.96°N), India. These observations provide spatio‐temporal evolution and dynamics of the F region FAIs occurring beyond the equatorial ionization anomaly (EIA) crest (22°–25°N magnetic latitude), which are the first of their kind. Radar echoes from the F region FAIs displayed plume structures occurring in the altitude range of 190–520 km and are found to be associated with equatorial plasma bubbles (EPBs). The altitude regions of the plume structures were traced along the magnetic field line to altitudes of 1,000–1,640 km at the geomagnetic equator and 250 km at 28°N geomagnetic latitude. Remarkably, the ascending plume structures were observed as early as 19:25 LT, which is unexpectedly early for the plumes to occur well beyond the EIA crest. The echoing structures were found to drift eastward with velocities in the range of 95–250 m s −1 ; echoing structures observed early in the evening moved faster than those observed late in the night. Doppler spectra associated with the rising plumes were remarkably broad with upward‐northward mean velocity of 100 m s −1 and more. These results are discussed in the light of current understanding of the equatorial and low latitude radar observations and altitude‐latitude evolution of EPBs.