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On 2 December 1999, the magnetometer stations in northern Finland registered\udstructured Pc1 activity simultaneously in three distinct frequency bands. Using simultaneous\udEISCAT radar measurements of the high-latitude ionosphere, we have studied the\udionospheric resonator properties during this multiband Pc1 event. The frequencies of the three\udstructured Pc1 bands were found to closely correspond to the second, third and fourth\udharmonic of the calculated fundamental frequency of the ionospheric Alfvén resonator (IAR). In\udaddition, those frequencies of the three pearl bands that were closest to the exact IAR\udharmonics were found to have the strongest intensities. The results demonstrate that the resonator\udcan have an important role on ground-based Pc1 activity over a notably large frequency\udrange, favoring transmission of waves with frequencies close to the resonator's\udeigenfrequencies. Since the frequencies of all three bands correspond to the maximum rather than\udthe minimum of the transmission coefficient, the traditional bouncing wave packet model\udneeds to be revised.  \ud<b>Key words.</b> Ionosphere (auroral ionosphere; ionosphere\udmagnetosphere interactions; wave propagation

An effect of the ionospheric Alfvén resonator on multiband Pc1 pulsations