Airglow-imaging observation of plasma bubble disappearance at geomagnetically conjugate points

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.

Shrinking equatorial plasma bubbles

“…Such observations indicate that it is unlikely for the observed shrinking phenomenon to be linked to the larger‐scale size variations occurring in the bottomside ionosphere. Further, in the earlier reports of Otsuka et al [] and Shiokawa et al [], the disappearance of EPBs or substantial weakening occurred at shorter time scales (within an hour). Whereas the observations presented here do not reveal sudden weakening or disappearance of EPBs.…”

“…Recent reports based on airglow observations revealed cases in which EPBs disappear due to interaction with traveling ionospheric disturbances (TIDs) [ Otsuka et al , ; Shiokawa et al , ]. The polarization electric fields associated with the TIDs are identified to have caused disappearance of the EPBs.…”

Coordinated Ground‐Based and Space‐Based Observations of Equatorial Plasma Bubbles

“…Typical density irregularities within EPBs can have different scale sizes of several to hundreds of kilometers, and EPBs can cover a broad altitudinal range from the bottomside ionosphere up to ∼1,000 km (Cherniak et al, 2019;Lühr et al, 2014). The spatial variation of EPBs can be derived from the dark streaks of emission depletion in optical observations from ground-based all-sky imagers (ASIs) or space-based ultraviolet (UV) imaging spectrographs (Comberiate & Paxton, 2010;Hickey et al, 2018;Kelley et al, 2003;Kil et al, 2009;Makela, 2006;Martinis et al, 2015;Otsuka et al, 2002;Shiokawa et al, 2015). It is generally accepted that EPBs are triggered under a favorable condition of the generalized Rayleigh-Taylor (R-T) instability at the bottomside of the F layer, where a steep vertical density gradient forms after the E layer disappears postsunset due to high recombination rate.…”

First Study on the Occurrence Frequency of Equatorial Plasma Bubbles over West Africa Using an All‐Sky Airglow Imager and GNSS Receivers

“…Plasma bubbles are more directly observed using airglow imagers (Kubota et al, ; Shiokawa et al, ); however, some research have used data from the GNSS to also observe plasma bubbles via some criteria that characterize known behaviors of the bubbles, for example, high ROTI (Rate of total electron content (TEC) index) and scintillation indices (Haase et al, ; Nishioka et al, ). Observationally, it has also not been established how plasma bubbles and scintillations/TEC fluctuations are associated in their occurrences.…”