Acoustic oscillations in the field-free, gravitationally stratified cavities under solar bipolar magnetic canopies

Details Acoustic oscillations in the field-free, gravitationally stratified cavities under solar bipolar magnetic canopies Acoustic oscillations in the field-free, gravitationally stratified cavities under solar bipolar magnetic canopies

Oct 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009a%26a...505..763k&link_type=abstract

Astronomy and Astrophysics, Volume 505, Issue 2, 2009, pp.763-770

Astronomy and Astrophysics

Astrophysics

10

Sun: Photosphere, Sun: Oscillations

Scientific paper

Aims: The main goal here is to study the dynamics of the gravitationally stratified, field-free cavities in the solar atmosphere, located under small-scale, cylindrical magnetic canopies, in response to explosive events in the lower-lying regions (due to granulation, small-scale magnetic reconnection, etc.). Methods: We derive the two-dimensional Klein-Gordon equation for isothermal density perturbations in cylindrical coordinates. The equation is first solved by a standard normal mode analysis to obtain the free oscillation spectrum of the cavity. Then, the equation is solved in the case of impulsive forcing associated to a pressure pulse specified in the lower lying regions. Results: The normal mode analysis shows that the entire cylindrical cavity of granular dimensions tends to oscillate with frequencies of 5-8 mHz and also with the atmospheric cut-off frequency. Furthermore, the passage of a pressure pulse, excited in the convection zone, sets up a wake in the cavity oscillating with the same cut-off frequency. The wake oscillations can resonate with the free oscillation modes, which leads to an enhanced observed oscillation power. Conclusions: The resonant oscillations of these cavities explain the observed power halos near magnetic network cores and active regions.

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