Figure 1: Power spectrum of the magnetic field observed at DU between 06:03 and 06:24 UT on May 9, 1979, and the cross-phase spectrum for the station pair DU-LL for the same time interval. Also included is the wave power of the H component at DU for a time interval (0002-0023 UT on the same day) when no pulsation activity was observed.
Figure 2: Eigenfrequencies identified by the cross-phase spectra for the H component of five pairs of adjacent stations. The latitude of the resonant field line is assumed to be at the center of the station pair. If a continuum of field line resonances is not present, this assumption will not be valid. A set of curves representing the first six harmonics following the calculation by Schulz .
Figure 3: The cross-phase spectra for the H component of DU and other lower-latitude stations at similar longitude. The separation of station pairs ranges from 175 km (DU-LL) to 800 km (DU-HA). The phase change generally increases with increasing separation.
Figure 4: Schematic diagram showing the cross-phase spectrum interpreted in terms of field line resonance theory. The top panel shows the phase as a function of latitudes for three examples of resonant L-shells with resonant frequencies , , . The phase difference between the signals observed at the two stations is shown in the bottom panel. The phase difference becomes greater as the separation of stations increases.
© 1998 American Geophysical Union