The photochemical system of the mesopause region is a nonlinear driven oscillator enforced by the diurnal-periodic solar radiation. Under idealized conditions this oscillator can display nonlinear effects such as period doubling cascades or chaos. We investigate what happens if this system is subjected to atmospheric diffusion. A high-resolution one-dimensional chemical system of the mesopause region has been established in order to answer this question. Strong diffusion destroys nonlinear effects, but for the lower values of the diffusion coefficient which are still of the order of magnitude of real values, different nonlinear effects occur. The most important effect consisted of the creation of a 2-day subharmonic oscillation. Such a 2-day oscillation of the concentration of chemical active species entails a corresponding oscillation of the chemical heating rates which feeds back to the dynamics of this region. The zonal wind influences the period of the oscillation so that the periods differ from the exact 48-hour value by a few hours depending on the wind velocity and its direction. We call this phenomenon the photochemical Doppler effect. ¿ 1999 American Geophysical Union