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

Ionospheric ions are energized to suprathermal energies (10-1000 ev) in the auroral zone. This produces a much larger quantity of escaping O+ ions tha n would otherwise occur, given typical ionospheric energies. Until recently , only limited work had been done relating ion upflow characteristics to ne arby, contemporaneous auroral forms. We present our results comparing the c haracteristics of the suprathermal outflowing O+ ions, as measured by, the Time-of-Flight Energy Angle Mass Spectrometer instrument on the Fast Aurora l Snapshot (FAST) spacecraft, to the auroral forms seen at the foot point o f the associated field line, as observed by the Ultraviolet Imager (UVI) on Polar. We present data from FAST nightside auroral zone passes between Jan uary 25 and February 11, 1997. During this interval, FAST made similar to 1 00 auroral zone passes in the Northern Hemisphere where the aurora was simu ltaneously imaged by the UVI. Close examination of 50 such passes shows tha t the regions where suprathermal O+ outflow occurs closely follow the local aurora regardless of how convoluted the auroral forms may be. Taken togeth er, these data show that the flux of escaping O+ ions increases by over a f actor of 100 as the auroral intensity in the 1600-1800 Angstrom band increa ses from 0 to 4 kR. Also, the delay between auroral intensification and sat uration O+ flux reaching 3000- to 4000-km altitude is similar to5-10 min.