  A set of strongly magnetized accreting white dwarfs (polars) shows
quasi-periodic oscillations (QPOs) with frequency about a Hz in their optical
luminosity. These Hz-frequency QPOs are thought to be generated by intensity
variations of the emitted radiation originating at the post-shock accretion
column. Thermal instability in the post-shock region, triggered by efficient
cooling process at the base, is believed to be the primary reason behind the
temporal variability. Here we study the structure and the dynamical properties
of the post-shock accretion column including the effects of bremsstrahlung and
cyclotron radiation. We find that the presence of significant cyclotron
emission in optical band reduces the overall variability of the post-shock
region. In the case of a larger post-shock region above the stellar surface,
the effects of stratification due to stellar gravity becomes important. An
accretion column, influenced by the strong gravity, has a smaller variability
as the strength of the thermal instability at the base of the column is
reduced. On the other hand, the cool, dense plasma, accumulated just above the
stellar surface, may enhance the post-shock variability due to the propagation
of magnetic perturbations. These characteristics of the post-shock region are
consistent with the observed properties of V834~Cen and in general with
Cataclysmic Variable sources that exhibit QPO frequency of about a Hz.
