Physics
Scientific paper
Apr 1968
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1968jatp...30..481d&link_type=abstract
Journal of Atmospheric and Terrestrial Physics, vol. 30, no. 4, pp. 481-486
Physics
4
Scientific paper
Published studies of ionospheric motions directly associated with geomagnetic variations have postulated three different models of the mechanism by which the interaction occurs. All the models predict relative amplitudes which agree with the observations within a few orders of magnitude, and their authors were unable to choose between them with any degree of certainty. The purpose of this communication is to report some new observations, and to discuss their bearing upon the three models. It is concluded that only one of the mechanisms is ordinarily compatible with the data, i.e. interaction with hydromagnetic waves at a height where the velocity of the waves is influenced by the ion-neutral particle collision frequency. The data and theory suggest that the interaction between the ionosphere and the fluctuating geomagnetic field which gives rise to the observed Doppler shifts at 2·7 and 4·6 MHz usually occurs in the daytime at heights between 135 and 300 km and somewhat lower down at night. During the daytime the hydromagnetic EM mode of propagation may be the Left circularly polarized mode propagating parallel to the geomagnetic field. At night, however, and particularly in the ease of Pt disturbances, the evidence supports the hypothesis that the principal hydromagnetic mode of propagation is the E--O, fast HM, or modified Alfvén wave propagating perpendicular to the geomagnetic field. There is also experimental evidence that this is not the only mechanism which may be involved in the association between rapid magnetic variations and ionospheric perturbations. In particular, infra-sonic waves perturbing, or produced by, electrojet currents appear to be observed on occasion.
Boyd Gary M.
Duffus H. J.
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