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UBC Theses and Dissertations

A theory for the generation of "intervals of pulsations of diminishing period" Roxburgh, Kenneth R.


Micropulsation data recorded at Palo Alto, California during 1963-4 and Ralston, Alberta during 1967 have been used to study "Intervals of pulsations of diminishing period" (IPDP). IPDP's are found to be generated in the dusk-midnight quadrant of the magnetosphere at an equatorial distance of about 6 earth radii. An intensive study of the Ralston data reveals that IPDP's occur during the expansive phase of magnetospheric substorms. It is proposed that IPDP's are generated by a cyclotron instability between energetic protons and left-hand ion cyclotron waves. Their main characteristics are determined by the perturbations of the dusk-midnight sector of the magnetosphere by magnetospheric substorms. One of the main disturbances in that region is a slow decrease and then sudden increase in the magnetic field corresponding to the buildup and decay of a partial ring current. IPDP's show an increase in midfrequency due to the change in the cyclotron instability frequency produced by the increasing magnetic field. This theory is tested by a comparison of frequency increase of IPDP's observed at Ralston and magnetic field increase in the magnetosphere observed by the ATS-1 satellite. Other conditions necessary for IPDP generation are then discussed. It is shown that different combinations of these conditions result in the generation of hm emissions and band type micropulsations.

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