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.