Equatorward auroral evening sector wave structures: characteristics and implications for magnetospheric dynamics.

Abstract:

On over 18 occasions during the last 3 observing seasons, high-sensitivity filtered all-sky cameras at Poker Flat Research Range have observed deep spatial modulation on the equatorward edge of the electron aurora. These modulations occur for approximately an hour between 5 and 8 UT (~ 16 to 19 MLT) and occur between ~ 64 and 68 degrees magnetic latitude. The wave structures have a ~ 50 to 150 km longitudinal wavelength and comparable latitudinal modulation (see Figure) and propagate westward at 600 to 800 m/s. The auroral form on the poleward side shows diffuse banded, pulsating structures. While the basic form is similar to Kelvin-Helmholtz structure, and the magnetic local time is often a region of strong convection during disturbed times, there is little evidence of shear at the edge or vorticity of the forms, which would be expected for K-H instabilities. The form is also consistent with ballooning or Rayleigh-Taylor instabilities, although the depth of modulation remains static. We will show examples and discuss the conditions under which they occur, and how the ionospheric observed parameters map to the magnetosphere under reasonable conditions. These structures are of interest because they indicate an instability at the equatorial boundary of the electron aurora during disturbed conditions and have the potential to be a method to discern plasma sheet boundary conditions remotely.