LONG-TERM VARIATIONS IN THE NEUTRAL GAS COMPOSITION OF THE THERMOSPHERE OVER NORILSK (2003-2013)
Seasonal variations in relative values of the main gas components of the thermosphere [O]/[N<sub>2</sub>] and [O<sub>2</sub>]/[O] were received at the station Norilsk during the period 2003-2013. Estimates were made using a technique the authors developed and data from the Norilsk digisonde (69° N, 88° E) for heights below the ionospheric layer F1 maximum under quiet and disturbed geomagnetic conditions in different seasons. We established that the [O<sub>2</sub>]/[O] ratio in the quiet and disturbed geomagnetic conditions in all seasons by the end of 2013 decreased from 10 to 20 % relative to the values of 2003. The [O]/[N<sub>2</sub>] ratio for the same conditions increased to 17 %.