CATEGORIES
Magneto-acoustic wave propagation in the solar atmosphere: vertical magnetic field, disturbance $\delta B$
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13.03.2015
Affiliation
Kiepenheuer-Institut für Sonnenphysik, Freiburg, Germany
Main category
Natural Sciences (Astrophysics and Astrononmy)
Caption
Magnetic field perturbations, $\delta B/B_0$, for di fferent time steps and for the scenario of a vertical magnetic fi eld. The magneto-acoustic wave propagates from the source (piston) located at (x; z) = (1000;-750) km. The horizontal line shows the equipartition level, where the sound speed equals the Alfven speed, $c_\mathrm{s}=c_\mathrm{A}$. The vertical lines represent magnetic field lines.
Further information
The wave is launched below the equipartition level by the piston as a predominantly acoustic wave. Upon reaching the equipartition level, where the Alfven speed reaches the sound speed, $c_\mathrm{s}=c_\mathrm{A}$, the acoustic wave is partially transmitted, and changes from the fast to the slow branch of the magneto-acoustic waves. This slow mode is then guided along the magnetic field lines into the higher layers of the atmosphere . The part of the wave energy that is not transmitted, is converted into the fast magnetic mode. This fast mode emerges from the equipartition level and is then refracted due to the high gradient of the Alfven speed.