Source regions of long-period pulsation events in electron precipitation and magnetic fields at South Pole Station

Details Source regions of long-period pulsation events in electron precipitation and magnetic fields at South Pole Station Source regions of long-period pulsation events in electron precipitation and magnetic fields at South Pole Station

Mar 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994jgr....99.3869p&link_type=abstract

Journal of Geophysical Research (ISSN 0148-0227), vol. 99, no. A3, p. 3869-3877

Other

10

Antarctic Regions, Electron Precipitation, Geomagnetic Micropulsations, Magnetic Equator, Time Measurement, Wave-Particle Interactions, Magnetometers, Riometers

Scientific paper

Pulsation events with long (100-1000 s) periods with a consistent frequency in both particle precipitation and surface geomagnetic field variations have been reported in the past from measurements made at various geomagnetic latitudes. An examination of broad beam riometer and magnetometer data from South Pole Station for the interval from 1982 to 1989 revealed nearly 200 such events. The onset times of these events were determined, and the results compared with predictions based on the work of Coroniti and Kennel (1970). This mechanism ascribes the occurrence of correlated magnetic and precipitation pulsations to ultra low frequency (ULF) modulation of equatorial very low frequency (VLF) wave-particle interactions. For this reason, VLF data from South Pole Station were also examined. Taking into consideration the ULF wave and particle transit times from an interaction region near the magnetic equator to the ground leads to an expectation that the onset of pulsations in the magnetometer data will lag the onset of pulsations in the riometer data by several minutes. This disparity in onset times, together with modulation of VLF emissions in the 0.5-1 kHz band, serves as an important indicator of whether or not an event can be explained by the above-cited theory. While about a third of the events fit the prediction of Coroniti and Kennel, another third do not. In these events, the onset of magnetic and precipitation pulsations is nearly simultaneous, and possible alternative generation mechanisms are explored. In the remaining third of the events, magnetic pulsations begin substantially earlier than precipitation pulsations. Events of this type appear at first to be inexplicable in terms of any transit time argument. However, data from the imaging riometer at South Pole Station indicate that this third class of events is probably not physically distinct from the first two but is the result of the differing areas to which the riometer and magnetometer are sensitive and can be accounted for by considering the effects of transverse motion of a persistent precipitation region.

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