We present new results of an international joint observing campaign, which was carried out in September 2000 to study the oscillatory behaviour of solar active regions. We concentrate on oscillations in the lower layers of the solar atmosphere as observed with the Michelson Doppler Imager (MDI, Scherrer et al. 1995, Sol. Phys., 162, 129). The resulting photospheric oscillation power maps are compared with chromospheric maps from simultaneous UV continuum data (taken with the TRACE instrument).

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... rom a magnetic field extrapolation of the MDI magnetograms we infer that the reduction in chromospheric high frequency power and enhancement of photospheric high frequency power may be explained by the interaction of acoustic waves with the magnetic canopy.