LOWER THERMOSPHERIC COMPOSITION CHANGES DERIVED FROM OPTICAL AND RADAR DATA TAKEN AT SONDRE STROMFJORD DURING THE GREAT MAGNETIC STORM OF FEBRUARY 1986

Several nights of optical and radar data were obtained from February 3 to 10, 1986 at Sondre Stromfjord, Greenland during a great geomagnetic storm when Ap reached 202. These data, excluding O I (630.0 nm), were used to monitor changes in O and O2 densities in the region from 100 to 200 km and are consistent with results of Hecht et al. (1989) wherein the O I (630.0 nm) emission was used. That is, there were large depletions of O in the E region during the peak of the storm. Using 24-hour Ap values both MSIS-83 and MSIS-86 underestimated the depletion of O during the storm. MSIS-86 did noticeably worse than did MSIS-83, probably a result of the low exospheric temperature predicted by MSIS-86. However, when 3-hour ap values were used both models did better in predicing the measured O depletions, although MSIS-86 again was less successful than was MSIS-83. The data results also show that the enhancements in O2 were less than predicted by MSIS models in either mode. From 0200-0230 UT on February 9, 1986, a time just after the peak of geomagnetic activity as measured by Kp, the O mixing ratio near 135 km was found to increase by nearly a factor of 2. This increase is consistent with the passage of an atmospheric gravity wave through this altitude region providing that the scale height of O above 140 km is greater than predicted by the model.