| Summary: | Short period geomagnetic micropulsations termed IPDPs (Intervals of Pulsations of Diminishing Period) are investigated using ground station data, geosynchronous satellite magnetograms, and the Kp and Dst geomagnetic indices. A model for the generation of IPDPs is described, and consideration is given to three mechanisms which could be responsible for the IPDP frequency rise: the inward motion, azimuthal drift, and increasing background magnetic field mechanisms. A simplified IPDP generation model containing the first two of these mechanisms is tested by computer simulation. Results from this simulation indicate the possibility of significant source region inward motion without actual plasmapause displacement, and the possibility of eastward developing IPDPs. Using amplitude variations along a north-south line of ground stations, two methods, each applicable under different ionospheric propagation conditions, are developed for quantitatively determining the inward motion of the IPDP source region. A system for qualitatively determining the potential influence of the increasing background field mechanism on an IPDP using the Dst index and geosynchronous satellite magnetograms is also formulated. Lastly, a technique for the assessment of the effects of the azimuthal drift mechanism, in conjunction with the inward motion mechanism, is developed. This technique assumes that only these two mechanisms are operating. In addition to addressing the frequency shift mechanisms, it provides estimates of the injection boundary position and the magnitude of any (ring current created) magnetic field depression in the IPDP source region. The frequency rises of two IPDPs are analyzed in detail using these methods. In both cases, the inward motion effect is the dominant factor in producing the frequency rise, with the increasing background field mechanism having no significant effect. The azimuthal drift mechanism is a secondary factor in creating one event's frequency rise, and actually suppresses the frequency rise of the other event. The computer simulation calculations also generally show the inward motion mechanism to be the dominant effect in producing IPDP frequency rises. Longitudinal variations within an IPDP event are also examined. The results of this examination are consistent with the IPDP generation model used here, which includes showing significant variations between stations spaced comparatively closely in longitude. === Science, Faculty of === Earth, Ocean and Atmospheric Sciences, Department of === Graduate
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