Observations show the increase of high-frequency wave power nearmagnetic network cores and active regions in the solar loweratmosphere. This phenomenon can be explained by the interaction ofacoustic waves with a magnetic field. We consider small-scale,bipolar, magnetic field canopy structure near the network cores andactive regions overlying field-free cylindrical cavities of thephotosphere. Solving the plasma equations we get the analyticaldispersion relation of acoustic oscillations in the field-freecavity area. We found that the =1 mode, where is azimuthalwave number, cannot be trapped under the canopy due to energyleakage upwards. However, higher (≥2) harmonics can beeasily trapped leading to the observed acoustic power halos underthe canopy.
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