Recent Results of the Remote Sensing of the O/N2 Ratio in the 100 to 200 Km Altitude Region

Abstract:

The O/N2 ratio is a sensitive indicator of dynamical changes in the composition of the lower Thermosphere. In the auroral zone the deposition of auroral energy (either through particle precipitation or Joule heating) can produce changes in vertical winds causing a decrease in the O/N2 ratio. Horizontal winds may transport O-depleted air away from the auroral zone causing composition changes in the latitude regions equatorward of the auroral zone. Large waves and tides may also affect composition. To measure such composition changes a number of complimentary remote sensing techniques exist. In the auroral zone ground-based photometers have been sued to monitor, at night, variations of the column O/N2 at a single location as a function of time. Satellite observations (most notably the GUVI instrument on TIMED) provide column O/N2 variations during the daytime as a function of latitude at a nearly fixed local time. Rockets have recently been shown to be able to measure vertical variations in an auroral arc providing altitude-based measurements. Here we review some of the most recent results with an emphasis on comparison with the model predictions of MSIS.