Figure 4. Horizontal power spectra of observatories at Srobarova, Slovakia, and Tihany, Hungary, on Jan. 9, 1998. Local noon is at 10:00 UT, with ULF energy nearly symmetric at this time. Note the slight attenuation from outer to inner L-shell.
Figure 5. Horizontal Cross-Spectra between Srobarova & Tihany, Jan. 9, 1998. The amplitude ratio (Figure a) and phase difference (Figure b) plots reveal dayside pulsation resonance at 50 mHz.
Figure 6. Cross-Spectra between Srobarova & Tihany, on March 6, 1997.
Figure b depicts strong phase difference signatures especially at 14:00 and 16:00. Note that for these strong signatures the phase increases almost proportionally with frequency, revealed as constant time difference of 6 and 9 seconds respectively in Figure c, revealing that the ULF energy arriving at Srobarova is nearly an echo of the energy arriving at Tihany.
Figure 7. Cross-Correlation between Srobarova & Tihany, on March 6, 1997. This time-domain correlation shows time shifted signals; note the narrow banded pulses in Figure c at 14:30 and 16:30 here show as 7 and 10 second shifts. There is then a change of shift from 10 to 1 second starting at 17:00.
Figure 8. Magnetograms of Srobarova and Tihany, on Sept. 21, 1997.
10 minute time plot starting at 14:30 of the comparative horizontal and declination magnetic components observed at Srobarova, Slovakia and Tihany, Hungary. There is a frequency independent time lead of about 6 seconds of Tihany over Srobarova.
Figure 9. Refined spectra of Srobarova and Tihany, with waveforms above spectra. The sample is 1024 seconds starting at 14:23 UT, using a reassigned smoothed pseudo Wigner Ville distribution. Most of the energy is below 30 mHz (Courtesy of Zoltan Voros).
Figure 10. Horizontal Cross-Spectra between Srobarova and Tihany during Heavy Pulsation Activity in September of 1997.
This wide bandwidth of activity has an unusually long time duration, extending well into the nightside. Note in Figure 3.6.4b how the phase difference increases at a low frequency and increases as the frequency increases, very prominent at the magnetic noon at 9:30 UT. Figure c show this as a near constant time displacement of 4 seconds.
Figures 11. Declination Cross-Spectra between Srobarova and Tihany during Heavy Pulsation Activity in September of 1997.
As with the horizontal component, the declination component has both matching pulsation activity and time difference signature, generally uncommon. Also there is the time displacement of 4 seconds.
Figure 12. Magnetograms between Srobarova and Tihany during Heavy Pulsation Activity on September 21, 1997.
Even though the wave is complex, there is a near constant time difference of signal arrival at Srobarova after Tihany.
