Study of a Global Pc5 Oscillation During the September 1998 Magnetic Storm

On September 15, 1998 (during the September 1998 GEM storm interval), Pc5 pulsations were observed at ground stations on both the dayside and the nightside of the Earth. These pulsations occurred approximately 15 hours after the onset of the main phase of the storm, just before the recovery phase. Cusp and polar cap latitude data from the MACCS array in northern Canada and the U.S. AGO array in Antarctica indicated that the pulsations had low power and a frequency of ~2 mHz. However, data from the CANOPUS array in Canada and the BAS AGO array in Antarctica, both in the auroral zone, indicated high power, 3-4 mHz Pc5 pulsations just equatorward of the cusp region. Their latitude dependent frequency suggests local field line resonances. At the mid to low latitude UCLA and Korean arrays the power of the pulsations dropped off greatly and the frequency dropped back to ~2 mHz. The frequency of the pulsations was the same at high latitude regions as it was at mid to low latitude regions. This same frequency was also observed at mid to low latitude stations at noon and 02:00 magnetic local time.