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

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 (10–500 km), while AMISR‐14 detects small‐scale irregularities (0.34 m). This study presents simultaneous observations of equatorial spread F (ESF) irregularities at 50–200 km scale sizes using the all‐sky imager, at 3 m scale sizes 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 submeter 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.

Formation and Evolution of Low‐Latitude F Region Field‐Aligned Irregularities During the 7–8 September 2017 Storm: Hainan Coherent Scatter Phased Array Radar and Digisonde Observations

“…The equatorial/low-latitude F region field-aligned irregularities (FAIs), also known as equatorial/low-latitude spread F, have been extensively studied for decades by using various instruments, such as VHF radars (e.g., Li et al, 2013;Tsunoda, 1980;Woodman & LaHoz, 1976;Yokoyama & Fukao, 2006), ionosondes (Abdu et al, 2003;W. S. Chen et al, 2006;Lee et al, 2005), optical airglow imager (Hickey et al, 2015;Otsuka et al, 2004;Sobral et al, 2009), Global Positioning System scintillation measurements (Li et al, 2010;Pi et al, 1997), and in situ satellites (Basu et al, 2001;Burke et al, 2004;Huang et al, 2012). Plasma irregularities in the ionosphere may cause rapid variations in phase and amplitude of radio signals and lead to detrimental effect on navigation and communication system (Woodman, 2009, and references therein).…”

Multi-instrumented observations of the equatorial F-region during June solstice: large-scale wave structures and spread-F

“…AMISR-14 is a modular, transportable phased-array radar system for ionospheric studies (Rodrigues et al 2015;Hickey et al 2015). For this campaign, we set operations in a new east-west scanning mode that attempted to produce a better description of the spatial distribution of F-region scattering structures than those produced by Rodrigues et al (2015).…”

“…The camera has four filters for observations of different nighttime airglow emissions (at 557.7, 630.0, 695.0, and 777.4 nm) and one filter for estimation of background emission (at 605.0 nm). Additional details about this system can be found in Hickey et al (2015). For this study, we focused on measurements of the 630.0 nm (red line) emission caused by the relaxation…”

Downward Drifting F‐Region Irregularity Observed Above an Eastward Drifting One Before Midnight on 4 March 2014

“…The bubbles can be observed by a variety of devices. They are recorded as dark bands in an airglow imager, indicating depleted‐density regions (e.g., Hickey et al., 2015; Huba et al., 2015; Otsuka et al., 2009). In the ionograms of an ionosonde, the range or frequency spread‐F traces can be recorded (e.g., Abdu et al., 2012; Wang et al., 2015).…”