Evolution of the spectral region around λ_c = 6579.7 Å for model r0e2 to illustrate the evolution of the Doppler velocity at maximum absorption as well as the peak blueshift. The value of λ_c corresponds to the air wavelength of the gf-weighted mean of the corresponding C II doublet. The Doppler velocity at the location of maximum absorption in this line follows closely the velocity of the photosphere shown in Fig. 6.