Geomagnetic conjugate observations of equatorial airglow depletions

Abstract

We report for the first time large‐scale equatorial F‐region airglow depletions extending to low‐midlatitudes in both hemispheres. The observational sites were located at low‐midlatitude geomagnetic conjugate points. Clear depletions of 630.0‐nm airglow intensity due to equatorial plasma bubbles were simultaneously observed with two all‐sky imagers at Sata, Japan (magnetic latitude 24°N), and its geomagnetic conjugate point, Darwin, Australia (magnetic latitude 22°S), on the night of November 12, 2001. Airglow depletion regions with east‐west scale sizes of 40–100 km extend poleward. The maximum apex altitude of the plasma bubbles is about 1,700 km over the geomagnetic equator. The depletions move eastward at about 100 m/s, without changing their structures. The Darwin depletion structures mapped onto the northern hemisphere along the geomagnetic field coincide closely with structures in the Sata images, even for the 40‐km structure. These observations indicate that plasma depletions in the equatorial ionosphere elongate along the geomagnetic field lines.