Abstract
We report the first observation of the disappearance of a plasma bubble over geomagnetically conjugate points. It was observed by airglow imagers at Darwin, Australia (magnetic latitude: −22°N) and Sata, Japan (21°N) on 8 August 2002. The plasma bubble was observed in 630-nm airglow images from 1530 (0030 LT) to 1800 UT (0300 LT) and disappeared equatorward at 1800 to 1900 UT (0300 to 0400 LT) in the field of view. The ionograms at Darwin and Yamagawa (20 km north of Sata) show strong spread-F signatures at approximately 16 to 21 UT. At Darwin, the F-layer virtual height suddenly increased from approximately 200 to approximately 260 km at the time of bubble disappearance. However, a similar F-layer height increase was not observed over the conjugate point at Yamagawa, indicating that this F-layer rise was caused not by an eastward electric field but by enhancement of the equatorward thermospheric wind over Darwin. We think that this enhancement of the equatorward neutral wind was caused by an equatorward-propagating large-scale traveling ionospheric disturbance, which was identified in the north-south keogram of 630-nm airglow images. We speculate that polarization electric field associated with this equatorward neutral wind drive plasma drift across the magnetic field line to cause the observed bubble disappearance.
Highlights
An equatorial plasma bubble is a spectacular structure in the equatorial F-region ionosphere caused by the ionospheric Rayleigh-Taylor instability (e.g., Woodman and La Hoz, 1976; Kelley, 1989)
We report a plasma bubble disappearance in the field of view of the 630-nm airglow images observed simultaneously at geomagnetically conjugate points
We suggest that the disappearance of the plasma bubble was caused by the polarization electric field associated with a large-scale traveling ionospheric disturbance
Summary
An equatorial plasma bubble is a spectacular structure in the equatorial F-region ionosphere caused by the ionospheric Rayleigh-Taylor instability (e.g., Woodman and La Hoz, 1976; Kelley, 1989). It causes significant scintillation of radio signals from satellites due to plasma irregularities (e.g., Basu et al 1996; Uma et al 2012; Park et al 2013). Makela et al (2006) showed the development of a secondary instability at the eastern wall of the plasma bubbles by using an airglow imager in Hawaii. Conjugacy of plasma bubbles along the geomagnetic field line has been confirmed using airglow imagers operated simultaneously in the northern and southern hemispheres (Otsuka et al 2002; Ogawa et al 2005; Martinis and Mendillo, 2007; Abdu et al 2009). Shiokawa et al (2004) showed that the conjugacy is maintained even during the growth phase of the plasma bubbles toward higher latitudes
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