VARIATIONS OF O(<sup></sup><sup>1</sup>D) ATOM CONCENTRATION IN THE UPPER ATMOSPHERE CAUSED BY SOLAR FLUX VARIABILITY
Variations of O2 and O3 photolysis rate in the mesosphere and lower thermosphere caused by solar flux variability are analyzed in the interval 1979-2005. Vertical profile of O(1D) concentration as a function of solar activity level and solar zenith angle is studied. Peak of O(1D) concentration during twilight is revealed at 85-95 km altitudes.