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

Abstract

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 ULF modulation of equatorial 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.

Pc5 modulation of high energy electron precipitation: particle interaction regions and scattering efficiency

“…This dawn-side maximum is consistent with the results of earlier similar studies of riometer Pc5 activity (see, e.g. Nosé et al, 1998 andPaquette et al, 1994) and appears to be half of the in-situ distribution of high-energy electron pulsations reported by (Baker et al (1980) and Kremser et al (1998). Our results indicate an increase of a factor of 2 in Pc5 activity during the fall-winter (September-February).…”

“…The suggested that at least some Pc5 waves are caused by the local injection of high energy electrons into the morning sector and that a ground-observed Pc5 pulsation is the signature of the resonating small Birkland current system being split off from east to west by injected electrons. Paquette et al (1994) surveyed the South Pole magnetometer and riometer data for pulsations occurring in the 100-1000 s range. They identified pulsations occurring in both instruments but restricted their survey to dayside activity.…”

Case studies on the dynamics of Pi3 geomagnetic and riometer pulsations during auroral activations

“…We observed these pulsations in the magnetic field and in the energetic precipitation, but their existence in the optical aurora remains without confirmation, since the other time variations in the auroral activity efficiently shield the probable pulsation-type variations. Paquette et al (1994) studied simultaneous riometer and magnetic pulsation events that took place during the daytime. They tested the hypothesis suggested by Coroniti and Kennel (1970) which associates the coupled magnetic and precipitation pulsations with the ULF modulation of VLF waveparticle interactions that take place at the magnetospheric equator.…”

Alfven wave modulation of the auroral acceleration region

“…An extensive examination of 7 years of simultaneous riometer and magnetometer data from South Pole station by Paquette et al (1994) showed that only about a third of Pc4-5 events fit the predictions of Coroniti and Kennel, while in other events the onset of magnetic and precipitation pulsations was nearly simultaneous, and possible alternative generation mechanisms are to be explored.…”

“…The idea of quasiperiodic precipitation owing to the interactions of electrons with VLF turbulence was further developed by Davidson (1990) and Demekhov and Trakhtengerts (1994). However, quite often investigation of electron precipitation associated with ULF pulsations did not reveal either compressional pulsations (Nose et al, 1998) or background VLF turbulence (Paquette et al, 1994). Moreover, taking into consideration the ULF wave and electron transit times from an interaction Copy right c The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRA-PUB.…”