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| Titel |
Observations of Pc 3-4 and Pi 2 geomagnetic pulsations in the low-latitude ionosphere |
| VerfasserIn |
R. A. Marshall, F. W. Menk |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 17, no. 11 ; Nr. 17, no. 11, S.1397-1410 |
| Datensatznummer |
250013833
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| Publikation (Nr.) |
 copernicus.org/angeo-17-1397-1999.pdf |
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| Zusammenfassung |
Day-time Pc 3–4 (~5–60 mHz) and night-time Pi
2 (~5–20 mHz) ULF waves propagating down through the ionosphere can cause
oscillations in the Doppler shift of HF radio transmissions that are correlated
with the magnetic pulsations recorded on the ground. In order to examine
properties of these correlated signals, we conducted a joint HF
Doppler/magnetometer experiment for two six-month intervals at a location near L
= 1.8. The magnetic pulsations were best correlated with ionospheric
oscillations from near the F region peak. The Doppler oscillations were in phase
at two different altitudes, and their amplitude increased in proportion to the
radio sounding frequency. The same results were obtained for the O- and X-mode
radio signals. A surprising finding was a constant phase difference between the
pulsations in the ionosphere and on the ground for all frequencies below the
local field line resonance frequency, independent of season or local time. These
observations have been compared with theoretical predictions of the amplitude
and phase of ionospheric Doppler oscillations driven by downgoing Alfvén mode
waves. Our results agree with these predictions at or very near the field line
resonance frequency but not at other frequencies. We conclude that the majority
of the observations, which are for pulsations below the resonant frequency, are
associated with downgoing fast mode waves, and models of the wave-ionosphere
interaction need to be modified accordingly.
Key words. Ionosphere (ionosphere irregularities) ·
Magnetospheric physics (magnetosphere-ionosphere interactions) · Radio science
(ionospheric physics) |
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