The relationship between suprathermal heavy ion outflow and auroral electron energy deposition: Polar/Ultraviolet Imager and Fast Auroral Snapshot/Time‐of‐Flight Energy Angle Mass Spectrometer observations

Abstract

Ionospheric ions are energized to suprathermal energies (10–1000 eV) in the auroral zone. This produces a much larger quantity of escaping O+ ions than would otherwise occur, given typical ionospheric energies. Until recently, only limited work had been done relating ion upflow characteristics to nearby, contemporaneous auroral forms. We present our results comparing the characteristics of the suprathermal outflowing O+ ions, as measured by the Time‐of‐Flight Energy Angle Mass Spectrometer instrument on the Fast Auroral Snapshot (FAST) spacecraft, to the auroral forms seen at the foot point of the associated field line, as observed by the Ultraviolet Imager (UVI) on Polar. We present data from FAST nightside auroral zone passes between January 25 and February 11, 1997. During this interval, FAST made ∼100 auroral zone passes in the Northern Hemisphere where the aurora was simultaneously imaged by the UVI. Close examination of 50 such passes shows that the regions where suprathermal O+ outflow occurs closely follow the local aurora regardless of how convoluted the auroral forms may be. Taken together, these data show that the flux of escaping O+ ions increases by over a factor of 100 as the auroral intensity in the 1600–1800 Å band increases from 0 to 4 kR. Also, the delay between auroral intensification and saturation O+ flux reaching 3000‐ to 4000‐km altitude is ∼5–10 min.