1996 Volume 48 Issue 11 Pages 1421-1430
In order to understand the characteristics of lower-latitude Pi 2 geomagnetic pulsations along a magnetic meridian, we have analyzed 1 year's data from the Adelaide (geomagnetic latitude Ψ=-46.72°), Birdsville (-37.08°), Weipa (-23.06°), Guam (9.02°), Chichijima (20.65°), Kagoshima (25.23°), and Moshiri (37.76°) stations along the 210° magnetic meridian. The characteristics of the lower-latitude (|Ψ| < 50°) Pi 2 pulsations are summarized as follows: (1) 80% of H- and D-component Pi 2 events show very similar wave forms and the same frequency component; (2) not only H-component Pi 2 events but also D-component Pi 2 events are observed within ±5 s; (3) H-component Pi 2 amplitudes are of almost the same order, but D-component Pi 2 pulsations have a minimum near the magnetic equator and increase exponentially from lower to higher latitudes; (4) the observed amplitudes of both H- and D-component Pi 2 pulsations are larger in the summer hemisphere than in the winter hemisphere. Results 1 and 2 show that lower-latitude Pi 2 pulsations are not propagating-mode but global-mode oscillations in the inner magnetosphere. Result 4 cannot be explained by the ordinary screening effect in the ionosphere but gives a clue to the unresolved generation mechanism of lower-latitude Pi 2 pulsations.
