Temporal Variation of Resonant Frequency at L=1.8
Physics Department, University of Newcastle, New South Wales, Australia 1
A technique based on the cross spectral phase of data recorded by closely spaced meridional ground stations is used to measure the eigenfrequency of magnetospheric field line resonances. This paper deals with Pc3 (22-100 mHz) ULF waves energy recorded by the University of Newcastle induction coil magnetometers located at Newcastle and Gloucester (L~1.8) and also two magnetometers at Launceston and Lemont (L~2.8). The resonances are seen almost every day for the daylight hours. At the lower latitude, there is often a decrease in frequency in the local morning. This is probably due to ionospheric refilling processes that load the magnetic field line and decrease the resonant frequency.
The paper in Geophysical Research Letters, Vol 18, p2293, 1991 showed data for 17 Oct, 1990. Here I have placed data recorded a few days later on 23 Oct, 1990. The FLR has been identified using a state vector polarisation technique. At the lower latitude (L=1.8), only a single harmonic is visible. However, at L=2.8 you can probably see at least 3 harmonics. We have seen multiple harmonics at the lower latitude and are currently preparing a paper on this.
Temporal Variation of Resonant Frequency at L=2.8