SOURCE REGIONS OF LONG-PERIOD PULSATION EVENTS IN ELECTRON-PRECIPITATION AND MAGNETIC-FIELDS AT SOUTH-POLE STATION

Citation
Ja. Paquette et al., SOURCE REGIONS OF LONG-PERIOD PULSATION EVENTS IN ELECTRON-PRECIPITATION AND MAGNETIC-FIELDS AT SOUTH-POLE STATION, J GEO R-S P, 99(A3), 1994, pp. 3869-3877
Citations number
24
Categorie Soggetti
Geosciences, Interdisciplinary","Astronomy & Astrophysics","Metereology & Atmospheric Sciences
Journal title
JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS
ISSN journal
21699380 → ACNP
Volume
99
Issue
A3
Year of publication
1994
Pages
3869 - 3877
Database
ISI
SICI code
2169-9380(1994)99:A3<3869:SROLPE>2.0.ZU;2-D
Abstract
Pulsation events with long (100-1000 s) periods with a consistent freq uency in both particle precipitation and surface geomagnetic field var iations have been reported in the past from measurements made at vario us geomagnetic latitudes. An examination of broad beam riometer and ma gnetometer 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 th e work of Coroniti and Kennel (1970). This mechanism ascribes the occu rrence of correlated magnetic and precipitation pulsations to ULF modu lation of equatorial VLF wave-particle interactions. For this reason, VLF data from South Pole Station were also examined. Taking into consi deration the ULF wave and particle transit times from an interaction r egion near the magnetic equator to the ground leads to an expectation that the onset of pulsations in the magnetometer data will lag the ons et of pulsations in the riometer data by several minutes. This dispari ty 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 ev ent can be explained by the above-cited theory. While about a third of the events fit the prediction of Coroniti and Kennel, another third d o not. In these events, the onset of magnetic and precipitation pulsat ions is nearly simultaneous, and possible alternative generation mecha nisms are explored. In the remaining third of the events, magnetic pul sations begin substantially earlier than precipitation pulsations. Eve nts of this type appear at first to be inexplicable in terms of any tr ansit 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 differ ing 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.