Low frequency geomagnetic ®eld ̄uctuations at low latitude during the passage of a higher pressure solar wind region

The passage of a higher pressure solar wind region at the Earth's orbit marked the onset of low latitude …L ˆ 1:6† ̄uctuations in the frequency range (0.8±5.5 mHz) for both the horizontal geomagnetic ®eld components. Spectral peaks mostly occur at the same frequencies as the spectral enhancements which appeared in the long term analysis of experimental measurements from the same station and were tentatively interpreted in terms of ground signatures of global magnetospheric modes. A comparison with simultaneous observations discussed by previous investigations allows us to conclude that the same set of frequencies is enhanced in a wide portion of the Earth's magnetosphere.