Concurrent observations at the magnetic equator of small-scale irregularities and large-scale depletions associated with equatorial spread F

TL;DR

This study presents simultaneous multi-scale observations of equatorial spread F irregularities using optical and radar instruments, revealing new insights into the spatial distribution of small- and large-scale plasma irregularities.

Contribution

It provides the first simultaneous comparison of small-scale, medium-scale, and large-scale irregularities at the magnetic equator, highlighting the spatial distribution and formation mechanisms of ESF irregularities.

Findings

Most radar echoes occur on the western wall of depletions.

Fewer echoes are observed on the eastern wall and center.

Irregularities are produced at sub-meter scales by the lower-hybrid-drift instability.

Abstract

In 2014 an all-sky imager (ASI) and an Advanced Modular Incoherent Scatter Radar consisting of 14 panels (AMISR-14) system were installed at the Jicamarca Radio Observatory. The ASI measures airglow depletions associated with large-scale equatorial spread F irregularities (10s-100s km), while AMISR-14 detects small-scale irregularities (0.34 m). This study presents simultaneous observations of equatorial spread F (ESF) irregularities at 10-100 km scales using the all sky-imager, at 3 m scales using the JULIA (Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere) radar, and at 0.34 m scales using the AMISR-14 radar. We compare data from the three instruments on the night of 20-21 August, 2014 by locating the radar scattering volume in the optical images. During this night no topside plumes were observed, and we only compare with bottomside ESF. AMISR-14 had five beams perpendicular to the magnetic field covering ~200 km in the east-west direction at 250 km altitude. Comparing the radar data with zenith ASI measurements, we found that most of the echoes occur on the western wall of the depletions with fewer echoes observed the eastern wall and center, contrary to previous comparisons of topside plumes that showed most of the echoes in the center of depleted regions. We attribute these differences to the occurrence of irregularities produced at sub-meter scales by the lower-hybrid-drift instability. Comparisons of the ASI observations with JULIA images show similar results to those found in the AMISR-14 and ASI comparison.