Global Pc5 wave activity observed using SuperDARN radars and ground magnetometers during an extended period of northward IMF

Observations are presented of long-lived global Pc5 ULF wave activity observed at a wide range of local times. The event was monitored in the high latitude ionosphere (similar to 60-80 degrees magnetic latitude) by several SuperDARN HF radars and 5 magnetometer chains in Scandinavia, Greenland, Canada, Alaska and Russia. The event coincided with a protracted period (similar to 36 h) of northward interplanetary magnetic field (IMF). The study focuses on 4 It during which distinct dawn/dusk asymmetries in the wave characteristics were observed with multiple field line resonance (FLR) structures observed in the dawn flank at 1.7, 2.6, 3.3, 4.2 and 5.4mHz and compressional oscillations in the dusk flank at 1.7 and 2.3 mHz. The data indicated an anti-sunward propagation in both the dawn and dusk flanks and a low azimuthal m number (vertical bar m vertical bar similar to 6) suggesting a generation mechanism external to the Earth's magnetosphere. A sudden increase in the solar wind dynamic pressure followed by a period of strongly northward, B-z dominated IMF, coincides with the observations and also a large increase in Pc5 wave power observed in the dawn flank. The observed enhancements in the wave activity and FLR structures are thought to be due to a Kelvin-Helmholtz driven waveguide mode. Additionally, there is no evidence that the frequencies of the FLRs are intrinsic to the solar wind. It thus seems that the frequencies were determined by the dimensions of the magnetospheric cavity. (c) 2006 Elsevier Ltd. All rights reserved.