VARIATIONS OF O(<sup></sup><sup>1</sup>D) ATOM CONCENTRATION IN THE UPPER ATMOSPHERE CAUSED BY SOLAR FLUX VARIABILITY
Variations of O<sub>2</sub> and O<sub>3</sub> photolysis rate in the mesosphere and lower thermosphere caused by solar flux variability are analyzed in the interval 1979-2005. Vertical profile of O(<sup></sup><sup>1</sup>D) concentration as a function of solar activity level and solar zenith angle is studied. Peak of O(<sup></sup><sup>1</sup>D) concentration during twilight is revealed at 85-95 km altitudes.