Influence of the Magnetic Field Inclination on Magneto-Acoustic-Gravity Waves in the Solar Atmosphere

Observations indicate that the magnetic field inclination plays an important role in wave propagation in sunspots and active regions. We explore the properties of these waves using the exact solution of MHD equations in a plasma permeated by an inclined magnetic field. The obtained K - Omega (wavenumber-frequency) diagrams indicate a decrease in the cut-off frequency with increasing magnetic field inclination. Typical 5-min waves are allowed to propagate upwards to the chromosphere if the magnetic field is sufficiently tilted. The ratio of Alfven speed to sound speed plays a key role in determining the cut-off frequency. We find very low cut-off frequencies even when this ratio is small at the bottom of the model atmosphere. Wave-associated energy is investigated over the whole K - Omega domain under consideration. As the magnetic field inclination increases, we find that modes become progressively magneto-acoustic through a large portion of the K - Omega domain. Gravity-related energy becomes increasingly secondary. This effect depends on location in the K - Omega diagram and the inclination angle of the magnetic field. At small K and Omega, we find that the cut-off frequency is low even though the gravity-associated energy density is not small.