Equatorial plasma bubbles: Vertically elongated wedges from the bottomside F layer

Abstract

We address the question regarding the two‐dimensional shape of equatorial plasma bubbles in the plane transverse to the geomagnetic field. By comparing the east‐west spatial relationship of ion‐density depletions measured in‐situ by the Atmospheric Explorer E (AE‐E) satellite to backscatter plumes measured by the ALTAIR radar, we show that plasma bubbles are vertically elongated depletions that extend upward from the bottom side of the F layer, in the form of tilted wedges, rather than more isotropically shaped but isolated structures. The shape of plasma bubbles is inferred from (1) ion density depletions that exceeded 99% in the ‘neck’ regions of plumes and (2) the eastward drift velocities of the plumes. The expected electrodynamics of vertically elongated plasma bubbles are consistent with the observations of large eastward drift velocities of plumes that are comparable to F region plasma drift measurements made at Jicamarca and to F region neutral wind measurements made at Kwajalein. The results also reveal that the west wall of large‐scale altitude modulations of the bottomside F layer that produces the primary plumes and bubbles becomes structured, and evolves with the generation of secondary plumes and bubbles.

Observations in equatorial anomaly region of total electron content enhancements and depletions

“…The characteristics and morphology of these depletions, that has been obtained mainly with the Jicamarca radar (e.g. Woodman and La Hoz, 1976), and substantiated by the satellite-based instruments and Altair radar observations (McClure et al, 1977;Dyson and Benson, 1978;Muldrew, 1980;Tsunoda, 1980;Tsunoda et al, 1982;Kil and Heelis, 1998;Yeh et al, 2001), are very well documented. Theoretical and observational investigations indiCorrespondence to: R. Pandey (pandey r@yahoo.com) cate that these depletions are generated on the bottomside of the nighttime equatorial F region and rise to higher altitudes due to the non-linear evolution of the generalized RayleighTaylor and E×B plasma instabilities (Kelley, 1989;Fejer et al, 1999).…”

Generation of large-scale equatorial F-region plasma depletions during lowrange spread-F season

“…As pointed out by Tsunoda et al (1982), a unique feature found to play a major role in the equatorial spread-F phenomena is the plasma "bubble", a localized depletion in F-region electron density. Plasma bubbles are aligned magnetic flux tubes and cover north-south distances across the magnetic equator of several thousand kilometers, with east-west dimensions of up to a few hundred kilometers.…”

The effects of the pre-reversal ExB drift, the EIA asymmetry, and magnetic activity on the equatorial spread F during solar maximum

“…Moreover, due to the nonlinear evolution, these instabilities would fully develop into vertically elongated wedges of plasma depletion from bottomside to topside of the F-layer (e.g. Tsunoda et al, 1982;Zalesack et al, 1982;Sultan, 1996).…”