First observations of the spatial structure of F region 3‐m‐scale field‐aligned irregularities with the Equatorial Atmosphere Radar in Indonesia

Abstract

This paper presents first results of spatial structure associated with 47‐MHz coherent backscatter from the low‐latitude F region in the Indonesian‐Thai longitude sector. The measurements were made with the Equatorial Atmosphere Radar (EAR), located on the geographic equator in West Sumatra, Indonesia (0.20°S, 100.32°E; dip latitude: 10.36°S). The active phased‐array of the EAR was used to perform rapid scans over a wide azimuth sector, with a temporal resolution that has heretofore been unachievable. Application of this unique capability is demonstrated herein to be effective in investigations of spatial structure of plasma bubbles and associated backscatter plumes. Most notably, tiny plumes are shown to grow rapidly while traversing from west to east across the scanned azimuth sector. Within an initial 20‐min period, backscatter intensity increased by more than 40 dB, and the area of the plume increased by a factor of about 20. Occasionally, plumes reached altitudes as high as 800 to 860 km in the scanned sector. These backscatter regions were traced along the magnetic field line to altitudes of 1200 to 1300 km over the geomagnetic equator. However, these tall structures are not so common over the EAR. The EAR observes fairly conspicuous patchy backscatter from the bottomside of a backscatter plume. The backscatter generated at the bottom of the plume appears to descend and eventually merge into the E region backscatter. The EAR has also observed a downward moving plume that continues for more than 4 hours, beginning at an altitude well into the topside of the ionosphere and descending below 300 km. The backscatter sometimes observed with the EAR at dip latitude of 10.36°S resembles that observed with the MU radar at mid‐latitudes. Investigation of these properties with the fast beam steerability of the EAR is expected to provide further insight into the nature of the source mechanism for plasma bubbles and plumes.