Mathematics – Logic
Scientific paper
Aug 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984jgr....89.6749r&link_type=abstract
Journal of Geophysical Research (ISSN 0148-0227), vol. 89, Aug. 1, 1984, p. 6749-6757. Research supported by the Natural Science
Mathematics
Logic
20
Geomagnetic Micropulsations, Magnetic Storms, Picosecond Pulses, Convective Flow, Kelvin-Helmholtz Instability, Morning, Polar Substorms, Power Spectra, Secular Variations, Solar Wind Velocity
Scientific paper
Since substorm expansive phase activity in the midnight sector and Pc 4,5 pulsation activity in the morning sector are both colocated with the auroral oval, it is logical to assume that sudden changes in plasma and field parameters in the oval would cause perturbations in the activity level of both types of activity. In an earlier study, Samson and Rostoker (1981) demonstrated that the frequency of Pc 4,5 pulsations on the dayside increased at the onset of a substorm expansive phase in the night sector. In that study, only pulsations recorded near noon were investigated for their frequency content. This paper considers the response of pulsation activity across the entire morning sector to substorm onsets near midnight. Using superposed epoch analyses it is demonstrated that the conclusions of Samson and Rostoker (1981) are valid across the morning sector. However close to dawn, Pc 5 activity appears to be initiated at substorm onset rather than decreasing by shifting frequency toward the Pc 5 band, as appears to be the case closer to noon. A model of Pc 4,5 activity is presented to explain this phenomenon in which the origin of the pulsations is proposed to be a Kelvin-Helmholtz instability at the interface between the low-latitude boundary and the central plasma sheet.
Rostoker Gordon
Samson John C.
Spadinger I.
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