Physics
Scientific paper
Aug 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001jgr...10615599w&link_type=abstract
Journal of Geophysical Research, Volume 106, Issue A8, p. 15599-15608
Physics
5
Magnetospheric Physics: Magnetosphere-Inner, Magnetospheric Physics: Magnetosphere/Ionosphere Interactions, Magnetospheric Physics: Mhd Waves And Instabilities, Magnetospheric Physics: Numerical Modeling
Scientific paper
Ultralow frequency (ULF) waves at the geomagnetic equator are studied by using a small magnetometer array and a one-dimensional electromagnetic wave model. Most ULF waves observed at low latitudes have been associated with shear Alfven mode hydromagnetic resonances in the plasmasphere. Near the equator it is difficult to excite these resonances, and the wave activity is attributed to fast mode waves. The phase difference data recorded at longitudinally spaced, equatorial magnetometers shows a marked change around dawn when one station is sunlit while the other is still in darkness. The phase structure with latitude also shows large phase shifts near the equator, in agreement with previous studies. A model of ULF wave propagation through the equatorial ionosphere is presented and used to compare with the observed amplitude and phase properties. It is shown that the observed frequencies are in the vicinity of the wave cutoff frequency where the phase structure becomes complicated. For frequencies above the cutoff, the phase structure across dawn is directly related to dawn-associated changes in electron density in the ionosphere.
Brand Kate
Foulkes K.
Fraser Brian J.
Menk Frederick W.
Saka O.
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