We investigated meridional and seasonal variations in small-vertical-scale (wavelengths 0.5--3 km) fluctuations of the ozone mixing ratio in the lower stratosphere using ozonesonde data covering wide longitudinal and latitudinal regions in all seasons. The generation of mixing ratio fluctuation is attributed to vertical advection and/or horizontal advection; the former was estimated from the potential temperature fluctuation and the vertical gradient of background mixing ratio, while the latter was obtained by subtracting the vertical advection component from the observed value. The results show that horizontal advection is always the major source of the mixing ratio fluctuation above the potential temperature of 700 K (~27 km altitude). Below 700 K, the source of the mixing ratio fluctuation depends on latitude; horizontal advection governs the mixing ratio fluctuations at high latitudes, vertical advection dominates at low latitudes, and horizontal advection is relatively dominant in winter--spring, while vertical advection is dominant in summer--autumn in the midlatitudes. These tendencies were confirmed by analyzing the correlation between the small-scale structures of the mixing ratio and the potential temperature. The synthetic distribution of the horizontal advection activity due to synoptic-scale motions calculated from assimilated meteorological data reproduced the seasonal, meridional, and altitudinal tendencies of the observed small-scale fluctuations, suggesting the major contribution of differential advection via large-scale winds.