Lower E region field-aligned irregularities studied using the Equatorial Atmosphere Radar and meteor radar in Indonesia

Abstract

This paper presents the first observations of lower E region echoes made with the Equatorial Atmosphere radar (EAR) located in West Sumatra, Indonesia (0.2°S, 100.32°E; dip latitude 10.36°S). The lower E region echoes observed over West Sumatra display descending layer structures with occasional descent to altitude as low as 85 km. The descending characteristics resemble the characteristics of tidal winds. Simultaneous observations of wind measured using a meteor radar show tidal wind fields with westward and northward winds above and eastward and southward winds below. The velocities of the field-aligned irregularities (FAI) observed by the EAR are found to agree quite well with the winds measured by the meteor radar. This suggests that in the collision dominated lower E region the FAI velocities represent essentially the neutral winds. The observations of low-altitude FAI are found to be consistent with the gradient drift instability except those occurring below 90 km, which deserves further investigation.