Low energy charged particle observations in the "auroral" magnetosphere: First results from the Akebono (EXOS-D) satellite.

Mukai, T.; Kaya, Nobuyuki; Sagawa, E.; Hirahara, Masafumi; Miyake, W.; Obara, Takao; Miyaoka, Hiroshi; Machida, S.; Yamagishi, Hisakazu; Ejiri, Masaki; Matsumoto, Hikaru; Itoh, Tohru

doi:10.5636/jgg.42.479

Cited by 70 publications

(40 citation statements)

References 19 publications

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“…We examined the current-voltage relationship in the acceleration region, using LEP (the low energy particle detector, Mukai et al, 1990) and MGF (the magnetometer, Fukunishi et al, 1990) data obtained by Akebono. The LEP data provide three-dimensional distribution functions of electrons and positive ions with a time resolution of ∼8 s. For magnetic field data, the 8-s (spin period) averaged fluxgate magnetometer data are used for the present analysis.…”

Section: Discussionmentioning

confidence: 99%

Current-voltage relationship in the auroral particle acceleration region

Mukai

Fukunishi

2004

Ann. Geophys.

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Abstract. The current-voltage relationship in the auroral particle acceleration region has been studied statistically by the Akebono (EXOS-D) satellite in terms of the charge carriers of the upward field-aligned current. The Akebono satellite often observed field-aligned currents which were significantly larger than the model value predicted by Knight (1973). We compared the upward field-aligned current estimated by three different methods, and found that low-energy electrons often play an important role as additional current carriers, together with the high-energy primary electrons which are expected from Knight's relation. Such additional currents have been observed especially at high and middle altitudes of the particle acceleration region. Some particular features of electron distribution functions, such as "cylindrical distribution functions" and "electron conics", have often been observed coinciding with the additional currents. They indicated time variability of the particle acceleration region. Therefore, we have concluded that the low-energy electrons within the "forbidden" region of electron phase space in the stationary model often contribute to charge carriers of the current because of the rapid time variability of the particle acceleration region. "Cylindrical distribution functions" are expected to be found below the time-varying potential difference. We statistically examined the locations of "cylindrical distribution function", and found that their altitudes are related to the location where the additional currents have been observed. This result is consistent with the idea that the lowenergy electrons can also carry significant current when the acceleration region changes in time.

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Section: Discussionmentioning

confidence: 99%

Current-voltage relationship in the auroral particle acceleration region

Mukai

Fukunishi

2004

Ann. Geophys.

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“…The satellite spin axis is directed toward the sun, and its spin period is about 8 s. The ion and electron instruments have the same view direction [Mukai et al, 1990] and also sweep their energy ranges in accord, from low-to high-energy steps and from high-to lowenergy steps. The electron beams and ion beams in Plate lb have low-energy.…”

Section: Datamentioning

confidence: 99%

Field‐aligned electron beams observed simultaneously with upflowing ion beams in the auroral acceleration region

Yoshioka¹,

Miyake²,

Mukai³

et al. 2000

J. Geophys. Res.

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Abstract. Upgoing, counterstreaming, and downgoing field-aligned electron beams observed simultaneously with upward ion beams in the auroral acceleration region on Akebono (Exos-D) satellite are studied statistically. These electron beams are narrowly collimated within the local loss cone, generally have lower energies per charge than the potential drop above the satellite, and are associated only with low-energy (<2 keV) ion beams. Their characteristics indicate that electrons of ionospheric origin are accelerated upward below the parallel auroral acceleration region (the region of upward electrostatic field) and are injected into the peripheral region of the parallel potential structure along the magnetic field line. Upflowing electron beams entering the bottom of the auroral acceleration region evolve into upgoing, counterstreaming, and possibly downgoing electrons, depending on the potential structure of the acceleration region. When the parallel potential drop is large enough to reflect the upflowing electrons back immediately within a short distance, then the electrons come down on the same field line and appear as counterstreaming electron beams. The upward and downward components of observed counterstreaming electron beams have the same energy and flux on average. Their occurrence decreases with increasing altitude. Upgoing electron beams are observed when the potential drop above the satellite is almost absent. Their occurrence shows no significant dependence on altitude, suggesting the penetration up to the top of parallel potential structure. A fraction of the downgoing electron beams are possibly caused by upflowing electron beams drifting to the adjacent magnetic field line being reflected back by the potential drop above the satellite. Some characteristics of downgoing electron beams, however, are different from those of upgoing and counterstreaming electron beams and suggest an alternative path of entering the parallel acceleration region.

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“…The Low Energy Particle (LEP) instrument on board (Mukai et al, 1990) was designed to observe energypitch angle distributions of auroral electrons and ions. It consists of two sets of E/Q analyzers separated at the symmetric position with respect to the satellite spin axis.…”

Section: Observationsmentioning

confidence: 99%

“…The observation of the Low Energy Particle (LEP) instrument (Mukai et al, 1990) on board Exos-D (Akebono) satellite has provided us with a large data set of ions and electrons over the polar region since its launch in 1989. From this data set, we can obtain the occurrence frequencies of ion conics as a function of altitude and conic angle.…”

Section: Introductionmentioning

confidence: 99%

Modeling of occurrence frequencies of ion conics as a function of altitude and conic angle

Miyake¹,

Mukai²,

Kaya³

2000

Ann. Geophys.

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Abstract. The occurrence frequencies of dayside ion conics with various conic angles are obtained as a function of altitude from Exos-D (Akebono) observations. We made a model calculation of ion conic evolution to match the observation results. The observed occurrence frequencies of ion conics with 80 to 90 conic angle are used as an input to the model and the occurrence frequencies of ion conics with smaller conic angles are numerically calculated at higher altitudes. The calculated occurrence frequencies are compared with the observed ones of ion conics with smaller conic angles. We take into account conic angle variation with altitude in both adiabatic and non-adiabatic cases, horizontal extension of ion conics due to E Â B drift, and evolution to elevated conics and ion beams in the model. In the adiabatic case, the conic angle decreases with increasing altitude much faster than was observed. The occurrence frequency of small-angle conics is much larger than the observed value without E Â B drift and evolution to the other UFIs. An agreement is obtained by assuming non-adiabatic variation of conic angles with altitude and an ion E Â B drift to gyro velocity ratio of 0.08 to 0.6, depending on geomagnetic activities.

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Low energy charged particle observations in the "auroral" magnetosphere: First results from the Akebono (EXOS-D) satellite.

Cited by 70 publications

References 19 publications

Current-voltage relationship in the auroral particle acceleration region

Current-voltage relationship in the auroral particle acceleration region

Field‐aligned electron beams observed simultaneously with upflowing ion beams in the auroral acceleration region

Modeling of occurrence frequencies of ion conics as a function of altitude and conic angle

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