Correlations between the peak flux density and the position angle of
  inner-jet in three blazars
  We aim to investigate the relation between the long-term flux density and the
position angle (PA) evolution of inner-jet in blazars. We have carried out the
elliptic Gaussian model-fit to the `core' of 50 blazars from 15 GHz VLBA data,
and analyzed the variability properties of three blazars from the model-fit
results. Diverse correlations between the long-term peak flux density and the
PA evolution of the major axis of the `core' have been found in $\sim$ 20% of
the 50 sources. Of them, three typical blazars have been analyzed, which also
show quasi-periodic flux variations of a few years (T). The correlation between
the peak flux density and the PA of inner-jet is positive for S5~0716+714, and
negative for S4~1807+698. The two sources cannot be explained with the
ballistic jet models, the non-ballistic models have been analyzed to explain
the two sub-luminal blazars. A correlation between the peak flux density and
the PA (with a T/4 time lag) of inner-jet is found in [HB89]~1823+568, this
correlation can be explained with a ballistic precession jet model. All the
explanations are based mainly on the geometric beaming effect; physical flux
density variations from the jet base would be considered for more complicated
situations in future, which could account for the no or less significance of
the correlation between the peak flux density and the PA of inner-jet in the
majority blazars of our sample.
