  Blue horizontal-branch (BHB) stars with $T_{\rm eff}$ approximately larger
than 11500 K show several observational anomalies. In globular clusters, they
exhibit low rotational velocities, abundance anomalies (as compared to cluster
abundances), photometric jumps and gaps and spectroscopic gravities lower than
predicted by canonical models. It is commonly believed that the low rotational
velocities of these stars permit atomic diffusion to be efficient in their
atmosphere thereby causing the observed anomalies. Recent detections of
vertical stratification of iron (and some other chemical elements) in several
BHB stars concur with this framework. In this paper, improved model atmospheres
that include the vertical stratification of the elements are applied to BHB
stars to verify if they can explain their observational anomalies. The results
from theoretical model atmospheres are consistent with the photometric jumps
and gaps observed for BHB stars in globular clusters. It is found that iron
stratification in the theoretical models and that obtained from observations
have similar tendancies. Our results also show that the spectroscopic gravities
obtained while using chemically homogeneous model atmospheres to fit
observations are underestimated. These results significantly strengthen the
belief that atomic diffusion is responsible for these BHB-star anomalies.
