We present the results of two-wavelength (353 and 511 nm) observations of vertical profiles of the scattering ratio R(H) at the Siberian Lidar Station obtained in January-March 2000. We have recorded an unusual increase in theR(H) ratio in the upper stratosphere at altitudes above 25 km. From analysis of meteorological conditions and the data of double-frequency lidar sensing we discuss the reasons for the observed variations of R(H), whose nature is most likely connected with the development of a sudden stratospheric warming. Such an unusual phenomenon with similar dynamics of the vertical structure of R(H) was observed over Tomsk in the winter of 1987.