The hot ion component of the magnetospheric plasma and some relations to the electron component-observations and physical implications

Hultqvist, B.

doi:10.1007/bf00212357

Cited by 37 publications

(22 citation statements)

References 94 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These count rates are due to the precipitation of plasma sheet ions, found to occur together with electron precipitation already in the ESRO 1 data (see e.g. Hultqvist, 1979). Most of the plasma sheet ions have energies above the upper energy limit of the Freja instrument, but ions from the plasma sheet, visible as a weak background flux at high energies, appears in most of the ion energy spectrograms.…”

Section: Observationsmentioning

confidence: 63%

Downward ion acceleration at auroral latitudes: cause of parallel electric field

Hultqvist

2002

Ann. Geophys.

View full text Add to dashboard Cite

Abstract.Observations with the Freja satellite at about 1700 km altitude of downward accelerated ions in the keV and sub-keV energy range are described and analysed. The observations show the following: (1) Processes involving velocity dispersion are not important; (2) Ion pitch-angle distributions are mostly somewhat field aligned but not far from isotropic, so the ions are effectively spread in pitch-angle; (3) As all ion species, H + , O + , and He + , are found to be accelerated to the same energy, the only possible known acceleration mechanism is a potential difference along the magnetic field lines; (4) No significant Birkeland current features are associated with the ion precipitation; (5) Precipitation of energetic electrons from the plasma sheet is always present when the downward accelerated ions are observed; (6) Ion precipitation is generally not seen in regions with primary auroral Birkeland currents associated with electron inverted-V distributions; (7) Precipitated ions are mostly observed at low and medium disturbance levels, but they are also found in strongly disturbed conditions; (8) Downward accelerated ions occur fairly frequently at auroral latitudes near Freja apogee altitudes and are seen at all local times. The present investigation is limited to the nightside.The above observational results are found to be consistent with the physical mechanism for producing a downwardpointing parallel electric field proposed by Hultqvist (1971). That mechanism is basically one of an ambipolar potential difference set up by the energetic electrons from the plasma sheet.

show abstract

Section: Observationsmentioning

confidence: 63%

Downward ion acceleration at auroral latitudes: cause of parallel electric field

Hultqvist

2002

Ann. Geophys.

View full text Add to dashboard Cite

show abstract

“…The downward proton ux incident at 800 km is assumed to be isotropic over the downward hemisphere (Hultqvist, 1979;Basu et al, 1987); its energy distribution is taken equal to a Maxwellian with a characteristic energy of 10 keV and with an energy¯ux of 1a erg Á cm À2 Á s À1 . The parameter is an attenuation parameter which is applied to the incident¯ux in order to take the spreading of the beam into consideration (Jasperse and Basu, 1982).…”

Section: In¯uence On Particle¯uxesmentioning

confidence: 99%

“…However, satellite and rocket measurements have shown that generally the pitch angle distributions of incident downward¯ux are roughly isotropic from 1 to several hundreds of keV in diuse aurora (Hultqvist, 1979;Basu et al, 1987) as well as in auroral arcs (Urban, 1981). Therefore, even though its action seems negligible, no de®nite conclusion can be drawn to date about the in¯uence of the magnetic mirroring eect on the red shift.…”

Section: Introductionmentioning

confidence: 99%

Proton transport model in the ionosphere. 2. Influence of magnetic mirroring and collisions on the angular redistribution in a proton beam

Galand

Lilensten²,

Kofman³

et al. 1998

Ann Geophysicae

View full text Add to dashboard Cite

Abstract. We investigate the in¯uence of magnetic mirroring and elastic and inelastic scattering on the angular redistribution in a proton/hydrogen beam by using a transport code in comparison with observations. H-emission Doppler pro®les viewed in the magnetic zenith exhibit a red-shifted component which is indicative of upward¯uxes. In order to determine the origin of this red shift, we evaluate the in¯uence of two angular redistribution sources which are included in our proton/ hydrogen transport model. Even though it generates an upward¯ux, the redistribution due to magnetic mirroring eect is not sucient to explain the red shift. On the other hand, the collisional angular scattering induces a much more signi®cant red shift in the lower atmosphere. The red shift due to collisions is produced by`1 -keV protons and is so small as to require an instrumental bandwidth`0X2 nm. This explains the absence of measured upward proton/hydrogen¯uxes in the Proton I rocket data because no useable data concerning protons`1 keV are available. At the same time, our model agrees with measured ground-based H-emission Doppler pro®les and suggests that previously reported red shift observations were due mostly to instrumental bandwidth broadening of the pro®le. Our results suggest that Doppler pro®le measurements with higher spectral resolution may enable us to quantify better the angular scattering in proton aurora.

show abstract

“…Wave-particle interactions were for a long time considered to be the main mechanism leading to particle precipitation, see, for example, a review by Hultqvist (1979). However, the ability of waves to produce the strong diffusion required to fill the loss cone isotropically is still under question.…”

Section: Introductionmentioning

confidence: 99%

Proton isotropy boundaries as measured on mid- and low-altitude satellites

et al. 2005

View full text Add to dashboard Cite

Abstract. Polar CAMMICE MICS proton pitch angle distributions with energies of 31-80 keV were analyzed to determine the locations where anisotropic pitch angle distributions (perpendicular flux dominating) change to isotropic distributions. We compared the positions of these mid-altitude isotropic distribution boundaries (IDB) for different activity conditions with low-altitude isotropic boundaries (IB) observed by NOAA 12. Although the obtained statistical properties of IDBs were quite similar to those of IBs, a small difference in latitudes, most pronounced on the nightside and dayside, was found. We selected several events during which simultaneous observations in the same local time sector were available from Polar at mid-altitudes, and NOAA or DMSP at low-altitudes. Magnetic field mapping using the Tsyganenko T01 model with the observed solar wind input parameters showed that the low-and mid-altitude isotropization boundaries were closely located, which leads us to suggest that the Polar IDB and low-altitude IBs are related. Furthermore, we introduced a procedure to control the difference between the observed and model magnetic field to reduce the large scatter in the mapping. We showed that the isotropic distribution boundary (IDB) lies in the region where R c /ρ∼6, that is at the boundary of the region where the non-adiabatic pitch angle scattering is strong enough. We therefore conclude that the scattering in the large field line curvature regions in the nightside current sheet is the main mechanism producing isotropization for the main portion of proton population in the tail current sheet. This mechanism controls the observed positions of both IB and IDB boundaries. Thus, this tail region can be probed, in its turn, with observations of these isotropy boundaries.

show abstract

The hot ion component of the magnetospheric plasma and some relations to the electron component-observations and physical implications

Cited by 37 publications

References 94 publications

Downward ion acceleration at auroral latitudes: cause of parallel electric field

Downward ion acceleration at auroral latitudes: cause of parallel electric field

Proton transport model in the ionosphere. 2. Influence of magnetic mirroring and collisions on the angular redistribution in a proton beam

Proton isotropy boundaries as measured on mid- and low-altitude satellites

Contact Info

Product

Resources

About