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On 24 August 2005,an impulse of solar wind dynamic pressure (Psw) hit the magnetosphere.Using the high resolution geomagnetic field data from 15 ground stations and the data from Geotail and TC-1,we have studied the geomagnetic pulsations at auroral latitudes driven by the sharp decrease of Psw at the trailing edge of the impulse.The results show that the sharp decrease of Psw can excite a global pulsation in the frequency range 4.3-11.6 mHz.The reversal of polarization between two auroral latitude stations,a larger power spectral density (PSD) close to resonant latitude and increasing frequency with decreasing latitude,all indicate that the pulsations are associated with field line resonance (FLR).