Observations of Magnetohydrodynamic Oscillations in the Solar Atmosphere with Properties of Alfven Waves

This paper reports observations of magnetohydrodynamic oscillations in the solar atmosphere with properties of Alfvén waves. These oscillations have periods in the 5 minute band. Phase relations between magnetic field variations and velocity variations are consistent with outgoing Alfvén waves. The aperture used for the observations is large, 20" x 20", and the velocity amplitude is reduced due to the resultant spatial filtering. If the magnetic and velocity variations are scaled up to be typical of the 5 minute oscillations as observed with 2" x 2" resolution, the outward energy flux is of order 3 x 107 ergs cm-2 s-1 in regions with a high magnetic field. Observations employing two parts of the Na D1 line separated by roughly 150-225 km in altitude of formation show phase lags in the magnetic field variations appropriate for outgoing waves. Velocity phase lags are very well determined and show that the vertical group velocity is larger in the magnetic regions than in the nonmagnetic regions. The power spectrum of the magnetic variations includes a peak at frequencies greater than the center of the 5 minute velocity oscillations superimposed on a background spectrum that includes substantial power at low frequencies.