  We present analytical and numerical models of a normal-polarity quiescent
prominence that are based on the model of Pikelner (Solar Phys. 1971, 17, 44 ).
We derive the general analytical expressions for the two-dimensional
equilibrium plasma quantities such as the mass density and a gas pressure, and
we specify magnetic-field components for the prominence, which corresponds to a
dense and cold plasma residing in the dip of curved magnetic-field lines. With
the adaptation of these expressions, we solve numerically the 2D, nonlinear,
ideal MHD equations for a Pikelner's model of a prominence that is initially
perturbed by reducing the gas pressure at the dip of magnetic-field lines. Our
findings reveal that as a result of pressure perturbations the prominence
plasma starts evolving in time and this leads to the antisymmetric
magnetoacoustic--gravity oscillations as well as to the mass-density growth at
the magnetic dip, and the magnetic-field lines subside there. This growth
depends on the depth of magnetic dip. For a shallower dip, less plasma is
condensed and vice-versa. We conjecture that the observed long-period
magnetoacoustic-gravity oscillations in various prominence systems are in
general the consequence of the internal pressure perturbations of the plasma
residing in equilibrium at the prominence dip.
