SIMBAD references

Applying 2D linear isothermal, perturbations to a magnetostatic arcade, we have obtained the MHD equations for the induced velocity field. We have considered the limit of very large wavenumbers in the direction perpendicular to the equilibrium magnetic field, which gives rise to what can be described as quasiperpendicular propagation. At comparatively low frequencies, the MHD wave equations decouple into two independent ordinary differential equations that can be easily solved either by numerical means or analytically, using the WKB method. The solutions are derived for an isothermal basic state when both the magnetic field intensity and the plasma density have arbitrary dependences on the flux function ψ. The obtained waves represent the Alfven and the slow magnetoacoustic modes, both modified by gravity and by the profile of the magnetic field. On the other hand, the high frequency domain yields only the fast MHD mode, that propagates along the tunnel of the arcade. A characteristic feature of these waves is that they are stable in the presence of a magnetic arcade, contrary to the case of a purely horizontal magnetic field when the magnetic buoyancy instability can set in.