The seasonal variation of auroral ion beams

Collin, H. L.; Peterson, W. K.; Lennartsson, O. W.; Drake, J. F.

doi:10.1029/1998gl900090

Cited by 62 publications

(71 citation statements)

References 15 publications

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“…Comparing radial distance bins below 2.5 R E for high K p conditions, the occurrence frequency in darkness is 0.05, which is 2.5 times higher than in sunlit conditions in the evening sector (18-22 MLT). Overall, this is in agreement with a previous study where a ratio of ∼3 was found in the occurrence frequency in darkness versus sunlit beams (Collin et al, 1998), although the beam selection criteria and thus the absolute occurrence frequencies are different in the two studies. It is also seen that in the evening sector between 2.5 and 3.5 R E the occurrence rate of ion beams is higher during darkness than during sunlit conditions, although the difference is not as large as below 2.5 R E .…”

Section: Mlt and Solar Illuminationsupporting

confidence: 82%

“…8 of Kondo et al (1990)), it was found that the ion fluxes increase as a function of K p , which probably reflects the general increase in auroral processes with K p . Using one year of TIMAS data it has also been found that ion beams below 10 000 km occur ∼3 times more often during wintertime than during summertime (Collin et al, 1998). This probably reflects the fact that during summertime, potential structures and their associated ion beams often reside at higher altitude, because of higher underlying ionospheric plasma density and thus were more often beyond the upper altitude limit of this study.…”

Section: Introductionmentioning

confidence: 89%

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The occurrence frequency of upward ion beams in the auroral zone as a function of altitude using Polar/TIMAS and DE-1/EICS data

2003

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Abstract.We study the occurrence frequency of upward auroral ion beams as a function of altitude using three years of Polar/TIMAS ion data combined with 11 years of DE-1/EICS ion data, in order to reach a complete altitude coverage between 5000 and 30 000 km. The most interesting result is that there is a peak in ion beam occurrence frequency and invariant energy flux and invariant particle flux at ∼3 R E radial distance. The peak exists at about the same altitude in both the evening and midnight MLT sectors. No solar cycle effects are found. We suggest that the peak could be due to a preferred altitude of auroral potential structures at ∼3 R E . To substantiate the suggestion, we also present a simple Monte Carlo simulation of ion beams. Another result is that the ion beam occurrence frequency and invariant (mapped to ionospheric altitude) energy and particle fluxes increase in the radial distance range 4-6 R E , suggesting that wave heating processes may take place in this altitude range.

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Section: Mlt and Solar Illuminationsupporting

confidence: 82%

Section: Introductionmentioning

confidence: 89%

The occurrence frequency of upward ion beams in the auroral zone as a function of altitude using Polar/TIMAS and DE-1/EICS data

2003

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“…As the electrons are accelerated by field-aligned electric field, protons are decelerated or accelerated upward. The observation of the seasonal variation of the upward ion beam was described in Collin et al (1998). Observations with the TIMAS instrument on board the POLAR satellite are similar to the seasonal variations of the intense electron aurora and are in agreement with the mechanism.…”

Section: Discussionsupporting

confidence: 57%

Global auroral conductance distribution due to electron and proton precipitation from IMAGE-FUV observations

et al. 2004

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Abstract. The Far Ultraviolet (FUV) imaging system on board the IMAGE satellite provides a global view of the north auroral region in three spectral channels, including the SI12 camera sensitive to Doppler shifted Lyman-α emission. FUV images are used to produce instantaneous maps of electron mean energy and energy fluxes for precipitated protons and electrons. We describe a method to calculate ionospheric Hall and Pedersen conductivities induced by auroral proton and electron ionization based on a model of interaction of auroral particles with the atmosphere. Different assumptions on the energy spectral distribution for electrons and protons are compared. Global maps of ionospheric conductances due to instantaneous observation of precipitating protons are calculated. The contribution of auroral protons in the total conductance induced by both types of auroral particles is also evaluated and the importance of proton precipitation is evaluated. This method is well adapted to analyze the time evolution of ionospheric conductances due to precipitating particles over the auroral region or in particular sectors. Results are illustrated with conductance maps of the north polar region obtained during four periods with different activity levels. It is found that the proton contribution to conductance is relatively higher during quiet periods than during substorms. The proton contribution is higher in the period before the onset and strongly decreases during the expansion phase of substorms. During a substorm which occurred on 28 April 2001, a region of strong proton precipitation is observed with SI12 around 14:00 MLT at ∼75 • MLAT. Calculation of conductances in this sector shows that neglecting the protons contribution would produce a large error. We discuss possible effects of the proton precipitation on electron precipitation in auroral arcs. The increase in the ionospheric conductivity, induced by a former proton precipitation can reduce the potential drop along field lines in the upward field-aligned currents by creating an opposite polarization electric field. This feedback mechanism possibly reduces the electron acceleration.

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“…Thus, it is possible that some ion heating on the nightside occurs above Freja altitudes in sunlit conditions. In a study of POLAR data from 5000 km altitude ion-beams were found predominantly during winter but transversely heated ion distributions were found with equal probabilities during summer and winter [Collin et al, 1998]. We note that distributions heated mainly at Freja altitudes would have been detected as field aligned beams in this investigation.…”

Section: Discussionmentioning

confidence: 88%

The importance of a dark ionosphere for ion heating and auroral arc formation

Hamrin

André

Norqvist

et al. 2000

Geophysical Research Letters

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Abstract.We present observations from the Freja Satellite to show that density reductions and ion heating at Freja heights are anticorrelated with solar illumination of the ionosphere. When the ionospheric foot-point of a flux-tube is in shadow, the ambient density is lower, transverse ion energization is more common and more intense, and the associated density cavities are deeper. In combination with the suggestion that the electrons must be accelerated to keV energies to carry an imposed current in a low density auroral cavity, these observations may explain the recent observation that auroras are more common when the ionosphere below is in darkness.

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The seasonal variation of auroral ion beams

Cited by 62 publications

References 15 publications

The occurrence frequency of upward ion beams in the auroral zone as a function of altitude using Polar/TIMAS and DE-1/EICS data

The occurrence frequency of upward ion beams in the auroral zone as a function of altitude using Polar/TIMAS and DE-1/EICS data

Global auroral conductance distribution due to electron and proton precipitation from IMAGE-FUV observations

The importance of a dark ionosphere for ion heating and auroral arc formation

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