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
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.