Unusually elongated, bright airglow plume in the polar cap F region: Is it a tongue of ionization?

Abstract

We report an event of unusually elongated, bright airglow plume, which is considered as an optical manifestation of tongue of ionization (TOI) in the central polar cap. This optical structure was detected with an all‐sky airglow imager at Resolute Bay (74.73°N, 265.07°E) during a large magnetic storm on December 15, 2006. The absolute optical intensity of the plume was ≈1 kR, which is much brighter than that of non‐stormtime polar cap patches. Two‐dimensional imaging capability of the all‐sky imager demonstrates that some meso‐scale structures (≈250–600 km) were embedded within the plume. Simultaneous ion density and drift measurements with the DMSP spacecraft strongly suggest that the plume was extending from the dayside as a narrow stream of dense plasma and thus is an optical manifestation of polar cap TOI. The DMSP data also implies that the possible source of the plume is a narrow stream of storm enhanced density (SED) transported from lower latitudes. The DMSP auroral particle observation demonstrates that the polar cap extremely expanded equatorward during this interval. This extreme expansion allowed the anti‐sunward convection to capture plasmas within the SED and deliver them deep into the polar cap as a luminous airglow plume. This observation claims that the plasma transport from the dayside lower latitudes plays an important role in controlling the plasma environment in the polar cap ionosphere during magnetic storms.