Solar magneto-atmospheric oscillations

Estimates of wave energy fluxes in the solar photosphere and chromosphere suggest that gravity waves carry more energy than co-spatial acoustic waves. This work presents an exploration of the upward propagation of gravity waves from the photosphere to the chromosphere, in a realistic model of the solar atmosphere. The purpose is to determine what happens to upward propagating gravity waves when they reach regions where the magnetic forces dominate. Wave motions are assumed linear and the atmosphere is static and horizontally invariant. Dispersion and ray diagrams provide insight into the mode con¬version mechanism. Numerical solution of the linear adiabatic wave equations quantify wave energy fluxes. The analysis shows that typically even weak magnetic fields cause the gravity wave to reflect back downwards as a slow magneto-acoustic wave well before the Alfven-acoustic equipartition level, and it fails to reach the chromosphere. However, highly inclined magnetic fields allow gravity waves to penetrate the equipartition level and experience substantial mode conversion to up-going Alfven waves, or field-guided acoustic waves. Wave energy fluxes are sensitive to the magnetic field orientation and short radiative damping times, but are insensitive to the magnetic field strengths over the range considered (lOG -100 G). The mode conversion pathways found in adiabatic analyses are preserved in the presence of damping. Mode conversion of gravity waves to Alfven waves is a possible pathway to the upper atmosphere for wave energy. The cause of the high frequency enhancement (the acoustic glory) in seismic power surrounding large active regions with complex field structures is not yet understood. This work presents an investigation of the properties of the seismic emission power and acoustic power of large active regions that have acoustic glories. Helioseismic holography is used to create seismic emission power maps for six large active regions with complex magnetic field structures. Acoustic glories are visible in high-frequency seismic emission power maps (5.0 mHz -7.0 mHz) for all active regions studied. The analysis of acoustic power about large active regions, in high and low frequency regimes, confirms behaviours that are consistent with the findings of previous analyses of smaller active regions. Several new properties of high frequency seismic emission power associated with large active regions are identified: The maximum enhancements in seismic emission and acoustic power occur at different spatial locations; acoustic glories are most prominent in seismic emission power maps in the 5.0 mHz -6.0 mHz bandwidth; the radius of the acoustic glory reduces as frequency increases; and the mean value of high frequency (above 5.0 mHz) seismic emission power for the active regions studied was enhanced at intermediate line-of-sight magnetic flux densities (50 G -300 G).