Statistics of high-altitude and high-latitude O&amp;lt;sup&amp;gt;+&amp;lt;/sup&amp;gt; ion outflows observed by Cluster/CIS

Arvelius, S.; Yamauchi, M.; Nilsson, Hans; Lundin, R.; Hobara, Y.; Rème, H.; Bavassano-Cattaneo, M. B.; Paschmann, G.; Korth, A.; Kistler, L. M.; Parks, G. K.

doi:10.5194/angeo-23-1909-2005

Cited by 28 publications

(43 citation statements)

References 21 publications

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“…Delcourt (1994) found that centrifugal effects could be important near the frontside magnetopause. This is in line with the results reported by Nilsson et al (2006b) and Arvelius et al (2005) who made simple estimates of the centrifugal acceleration based on high altitude Cluster spacecraft data, and found it to be significant.…”

Section: Introductionsupporting

confidence: 81%

“…The temporal term increased most with K p . In a previous study Arvelius et al (2005) found, based on essentially the same data set as in our study, that energization at altitudes above 7 R E was more prominent for high K p . The acceleration at higher altitude often show deceleration as well, see Fig.…”

Section: K P Dependencementioning

confidence: 86%

“…As shown by Nilsson et al (2006b) this similarity of the parallel bulk velocity for H + and O + ions is common already above the polar cap, from about 5 R E altitude. Ions at progressively higher altitudes are also further energized (Nilsson et al, 2004;Arvelius et al, 2005;Nilsson et al, 2006b). It is therefore of interest to study energization mechanisms in the high altitude polar cap.…”

Section: Introductionmentioning

confidence: 99%

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An assessment of the role of the centrifugal acceleration mechanism in high altitude polar cap oxygen ion outflow

et al. 2008

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Abstract. The role of the centrifugal acceleration mechanism for ion outflow at high altitude above the polar cap has been investigated. Magnetometer data from the four Cluster spacecraft has been used to obtain an estimate of magnetic field gradients. This is combined with ion moment data of the convection drift and the field-aligned particle velocity. Thus all spatial terms in the expression for the centrifugal acceleration are directly obtained from observations. The temporal variation of the unit vector of the magnetic field is estimated by predicting consecutive measurement-points through the use of observed estimates of the magnetic field gradients, and subtracting this from the consecutively observed value. The calculation has been performed for observations of outflowing O + beams in January to May for the years 2001-2003, and covers an altitude range of about 5 to 12 R E . The accumulated centrifugal acceleration during each orbit is compared with the observed parallel velocities to get an estimate of the relative role of the centrifugal acceleration. Finally the observed spatial terms (parallel and perpendicular) of the centrifugal acceleration are compared with the results obtained when the magnetic field data was taken from the Tsyganenko T89 model instead. It is found that the centrifugal acceleration mechanism is significant, and may explain a large fraction of the parallel velocities observed at high altitude above the polar cap. The magnetic field model results underestimate the centrifugal acceleration at the highest altitudes investigated and show some systematic differences as compared to the observations in the lower altitude ranges investigated. Our results indicate that for altitudes corresponding to magnetic field values of more than 50 nT a test particle Correspondence to: H. Nilsson (hans.nilsson@irf.se) model with a steady state magnetic field model, a realistic convection model and an initial velocity of about 20 k m s −1 at 5 R E should be able to reproduce the main part of our observational results.

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Section: Introductionsupporting

confidence: 81%

Section: K P Dependencementioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

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An assessment of the role of the centrifugal acceleration mechanism in high altitude polar cap oxygen ion outflow

et al. 2008

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“…Nilsson et al (2006) showed that the high altitude polar cap magnetosphere (6-12 R E geocentric distance) is not just a passive transport region, and that a significant perpendicular energization at high altitudes was a likely explanation for the reported measurements. Arvelius et al (2005) demonstrated that the statistical distribution of energetic ions (1 keV and above) in the 6-12 R E geocentric distance interval was not consistent with just a velocity filter effect in combination with a low altitude heating source. Nilsson et al (2006) found that O + is significantly transversely energized in the high altitude region (6-12 R E ), indicated both by increasing perpendicular temperatures with altitude as well as by a tendency towards higher perpendicular than parallel temperature for the highest observed temperatures.…”

Section: Introductionmentioning

confidence: 99%

Oxygen ion energization observed at high altitudes

et al. 2010

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Abstract. We present a case study of significant heating (up to 8 keV) perpendicular to the geomagnetic field of outflowing oxygen ions at high altitude (12 R E ) above the polar cap. The shape of the distribution functions indicates that most of the heating occurs locally (within 0.2-0.4 R E in altitude). This is a clear example of local ion energization at much higher altitude than usually reported. In contrast to many events at lower altitudes, it is not likely that the locally observed wave fields can cause the observed ion energization. Also, it is not likely that the ions have drifted from some nearby energization region to the point of observation. This suggests that additional fundamentally different ion energization mechanisms are present at high altitudes. One possibility is that the magnetic moment of the ions is not conserved, resulting in slower outflow velocities and longer time for ion energization.

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“…Transversely accelerated ions at altitudes ranging from a few hundred kilometers to several Earth radii at auroral and polar cusp latitudes have been observed (Klumpar et al, 1984;Winningham and Burch, 1984;Arnoldy et al, 1992;Lundin et al, 1995;Eklund et al, 1997;Moore et al, 1999;Huddleston et al, 2000;Arvelius et al, 2005). The ion acceleration through wave-particle interaction with plasma turbulence at high latitudes of the Earth's magnetosphere has generally been accepted to explain the origin of the above observations.…”

Section: Introductionmentioning

confidence: 88%

High-altitude and high-latitude O<sup>+</sup> and H<sup>+</sup> outflows: the effect of finite electromagnetic turbulence wavelength

et al. 2007

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Abstract. The energization of ions, due to interaction with electromagnetic turbulence (i.e. wave-particle interactions), has an important influence on H + and O + ions outflows in the polar region. The effects of altitude and velocity dependent wave-particle interaction on H + and O + ions outflows in the auroral region were investigated by using Monte Carlo method. The Monte Carlo simulation included the effects of altitude and velocity dependent wave-particle interaction, gravity, polarization electrostatic field, and divergence of auroral geomagnetic field within the simulation tube (1.2-10 earth radii, R E ). As the ions are heated due to wave-particle interactions (i.e. ion interactions with electromagnetic turbulence) and move to higher altitudes, the ion gyroradius ρ i may become comparable to the electromagnetic turbulence wavelength λ ⊥ and consequently (k ⊥ ρ i ) becomes larger than unity. This turns the heating rate to be negligible and the motion of the ions is described by using Liouville theorem. The main conclusions are as follows: (1) the formation of H + and O + conics at lower altitudes and for all values of λ ⊥ ; (2) O + toroids appear at 3.72 R E , 2.76 R E and 2 R E , for λ ⊥ =100, 10, and 1 km, respectively; however, H + toroids appear at 6.6 R E , 4.4 R E and 3 R E , for λ ⊥ =100, 10, and 1 km, respectively; and H + and O + ion toroids did not appear for the case λ ⊥ goes to infinity, i.e. when the effect of velocity dependent wave-particle interaction was not included; (3) As λ ⊥ decreases, H + and O + ion drift velocity decreases, H + and O + ion density increases, H + and O + ion perpendicular temperature and H + and O + ion parallel temperature decrease; (4) Finally, including the effect of finite electromagnetic turbulence wavelength, i.e. the effect of velocity dependent diffusion coefficient and consequently, the velocity dependent wave-particle interactions produce realistic H + and O + ion temperatures and H + and O + toroids, and this is, qualitatively, consistent with the observations of H + and O + ions in the auroral region at high altitudes.

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Statistics of high-altitude and high-latitude O<sup>+</sup> ion outflows observed by Cluster/CIS

Cited by 28 publications

References 21 publications

An assessment of the role of the centrifugal acceleration mechanism in high altitude polar cap oxygen ion outflow

An assessment of the role of the centrifugal acceleration mechanism in high altitude polar cap oxygen ion outflow

Oxygen ion energization observed at high altitudes

High-altitude and high-latitude O<sup>+</sup> and H<sup>+</sup> outflows: the effect of finite electromagnetic turbulence wavelength

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Statistics of high-altitude and high-latitude O&lt;sup&gt;+&lt;/sup&gt; ion outflows observed by Cluster/CIS

Cited by 28 publications

References 21 publications

An assessment of the role of the centrifugal acceleration mechanism in high altitude polar cap oxygen ion outflow

An assessment of the role of the centrifugal acceleration mechanism in high altitude polar cap oxygen ion outflow

Oxygen ion energization observed at high altitudes

High-altitude and high-latitude O&lt;sup&gt;+&lt;/sup&gt; and H&lt;sup&gt;+&lt;/sup&gt; outflows: the effect of finite electromagnetic turbulence wavelength

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Statistics of high-altitude and high-latitude O<sup>+</sup> ion outflows observed by Cluster/CIS

High-altitude and high-latitude O<sup>+</sup> and H<sup>+</sup> outflows: the effect of finite electromagnetic turbulence wavelength