We consider changes of the ozone vertical profile using Umkehr observations taken at Belsk (52 ¿N, 21 ¿E) by means of the Dobson spectrophotometer in the period 1963--1998. The ratio of ozone content in the Umkehr layers 1--4 (0--23.5 km) to total column ozone (layers 1--10) is used as a proxy characterizing the shape of the ozone profile. The long-term tendency in the ratio appears statistically insignificant for the periods 1963--1979 and 1980--1998. Analysis of the residuals from the multiple-regression model, which relates fluctuations in the measured daily UV doses (erythemally weighted) at Belsk with those in total ozone and global radiation (surrogate for the cloud and/or aerosol property variations) for the period 1993--1998, reveals that a 0.1 decrease (increase) of the ratio manifests as ~2.3% increase (decrease) of the daily dose relative to its normal value. Extreme change in the vertical structure of the atmosphere yields about a 5% change in the UV daily dose. The simulations by means of a radiative transfer model also show that possible changes of the vertical structure of the atmosphere are rather a minor source of day-to-day variations in surface UV radiation. It is suggested that the temporal variations of the ratio may give an insight into the year-to-year variations of dynamical processes affecting total ozone content in the Northern Hemisphere midlatitudes. ¿ 2000 American Geophysical Union