Abstract
Abstract. Observations show the increase of high-frequency wave power near magnetic network cores and active regions in the solar lower atmosphere. This phenomenon can be explained by the interaction of acoustic waves with a magnetic field. We consider small-scale, bipolar, magnetic field canopy structure near the network cores and active regions overlying field-free cylindrical cavities of the photosphere. Solving the plasma equations we get the analytical dispersion relation of acoustic oscillations in the field-free cavity area. We found that the m=1 mode, where m is azimuthal wave number, cannot be trapped under the canopy due to energy leakage upwards. However, higher (m≥2) harmonics can be easily trapped leading to the observed acoustic power halos under the canopy.
Highlights
Waves play an important role in the dynamics of the solar atmosphere
Observations show an increase of high-frequency power (ν>5 mHz) in the surroundings of active regions in velocity power maps sometimes called as photospheric power halos (Braun et al, 1992; Brown et al, 1992; Hindman and Brown, 1998; Jain and Haber, 2002)
We have studied the spectrum of acoustic oscillations in a cylindrical field-free cavity under a small-scale bipolar magnetic canopy in the solar atmosphere
Summary
Waves play an important role in the dynamics of the solar atmosphere. Observations show an increase of high-frequency power (ν>5 mHz) in the surroundings of active regions in velocity power maps sometimes called as photospheric power halos (Braun et al, 1992; Brown et al, 1992; Hindman and Brown, 1998; Jain and Haber, 2002). It has been shown that the quiet-Sun chromospheric magnetic network elements are surrounded by “magnetic shadows”, which lack the oscillatory power at higher frequency range (McIntosh and Judge, 2001; Krijger et al, 2001; Vecchio et al, 2007) Both the photospheric power halos and the chromospheric magnetic shadows probably reflect the same physical process of acoustic wave interaction with overlying magnetic field We suggest that granular cells may form field-free cylindrical cavities under the magnetic canopy due to the transport of magnetic flux towards boundaries These cavities may trap high-frequency acoustic oscillations, while the lower-frequency harmonics may propagate upwards in form of magneto-acoustic waves.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
