CHARACTERISTICS OF LOW-LATITUDE PI-2 PULSATIONS ALONG THE 210-DEGREESMAGNETIC MERIDIAN

In order to understand the characteristics of lower-latitude Pi 2 geom agnetic pulsations along a magnetic meridian, we have analyzed 1 year' s data from the Adelaide (geomagnetic latitude Phi = -46.72 degrees), Birdsville (-37.08 degrees), Weipa (-23.06 degrees), Guam (9.02 degree s), Chichijima (20.65 degrees), Kagoshima (25.23 degrees), and Moshiri (37.76 degrees) stations along the 210 degrees magnetic meridian. The characteristics of the lower-latitude (\Phi\ < 50 degrees) Pi 2 pulsa tions are summarized as follows: (1) 80% of H- and D-component Pi 2 ev ents 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 ar e observed within +/-5 s; (3) H-component Pi 2 amplitudes are of almos t the same order, but D-component Pi 2 pulsations have a minimum near the magnetic equator and increase exponentially from lower to higher l atitudes; (4) the observed amplitudes of both H- and D-component Pi 2 pulsations are larger in the summer hemisphere than in the winter hemi sphere. Results 1 and 2 show that lower-latitude Pi 2 pulsations are n ot propagating-mode but global-mode oscillations in the inner magnetos phere. Result 4 cannot be explained by the ordinary screening effect i n the ionosphere but gives a clue to the unresolved generation mechani sm of lower-latitude Pi 2 pulsations.