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

Ganushkina, N. Y.; Pulkkinen, Tuija; Kubyshkina, M. V.; Сергеев, В. А.; Lvova, E. A.; Yahnina, T. A.; Yahnin, A. G.; Fritz, T. A.

doi:10.5194/angeo-23-1839-2005

Cited by 28 publications

(38 citation statements)

References 29 publications

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“…Of the two mechanisms, the CSS process operates at all times and in all MLT sectors. A number of papers have identified CSS as the main (though not necessarily exclusive) mechanism for IB formation during quiet time (Ganushkina et al, ; Haiducek et al, ; Sergeev & Tsyganenko, ; Sergeev et al, ). However, at times EMIC scattering may cause the IB to be observed at a lower latitude than would occur if CSS were the operative mechanism.…”

Section: Introductionmentioning

confidence: 99%

The Role of Current Sheet Scattering in the Proton Isotropic Boundary Formation During Geomagnetic Storms

et al. 2019

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There is considerable evidence that current sheet scattering (CSS) plays an important role in isotropic boundary (IB) formation during quiet time. However, IB formation can also result from scattering by electromagnetic ion cyclotron waves, which are much more prevalent during storm time. The effectiveness of CSS can be estimated by the parameter K=Rcrg, the ratio of the field line radius of curvature to the particle gyroradius. Using magnetohydrodynamic and empirical models, we estimated the parameter K associated with storm time IB observations on the nightside. We used magnetic field observations from spacecraft in the magnetotail to estimate and correct for errors in the K values computed by the models. We find that the magnetohydrodynamic and empirical models produce fairly similar results without correction and that correction increases this similarity. Accounting for uncertainty in both the latitude of the IB and the threshold value of K required for CSS, we found that 29–54% of the IB observations satisfied the criteria for CSS. We found no correlation between the corrected K and magnetic local time, which further supports the hypothesis that CSS played a significant role in forming the observed IBs.

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Section: Introductionmentioning

confidence: 99%

The Role of Current Sheet Scattering in the Proton Isotropic Boundary Formation During Geomagnetic Storms

et al. 2019

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“…For the protons with energies ranging between a few tens and 100 keV, the boundary between adiabatic and nonadiabatic particle motion occurs near the center of the tail current sheet on the nightside at r ∼ 6 − 9 Re (e.g., Sergeev and Tsyganenko, 1982;Shevchenko et al, 2010;Wang et al, 2012;Yue et al, 2014). Tailward of that boundary a strong current sheet scattering (CSS) provides the nearly isotropic proton angular distributions in the tail plasma sheet (e.g., Ganushkina et al, 2005;Yue et al, 2014) whose precipitation forms an extended isotropic proton precipitation region, the proton auroral oval (Sergeev et al, 1983;Donovan et al, 2003;Meurant et al, 2007). The equatorward boundary at which the ratio of precipitated to trapped fluxes quickly drops down below 1 (called the isotropy boundary, IB) is usually sharply de-fined and well-observed at any particular energy.…”

Section: Introductionmentioning

confidence: 99%

Magnetospheric conditions near the equatorial footpoints of proton isotropy boundaries

et al. 2015

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Abstract. Data from a cluster of three THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft during February-March 2009 frequently provide an opportunity to construct local data-adaptive magnetospheric models, which are suitable for the accurate mapping along the magnetic field lines at distances of 6-9 Re in the nightside magnetosphere. This allows us to map the isotropy boundaries (IBs) of 30 and 80 keV protons observed by low-altitude NOAA POES (Polar Orbiting Environmental Satellites) to the equatorial magnetosphere (to find the projected isotropy boundary, PIB) and study the magnetospheric conditions, particularly to evaluate the ratio K IB (R c /r c ; the magnetic field curvature radius to the particle gyroradius) in the neutral sheet at that point. Special care is taken to control the factors which influence the accuracy of the adaptive models and mapping. Data indicate that better accuracy of an adaptive model is achieved when the PIB distance from the closest spacecraft is as small as 1-2 Re. For this group of most accurate predictions, the spread of K IB values is still large (from 4 to 32), with the median value K IB ∼ 13 being larger than the critical value K cr ∼ 8 expected at the inner boundary of nonadiabatic angular scattering in the current sheet. It appears that two different mechanisms may contribute to form the isotropy boundary. The group with K ∼ [4, 12] is most likely formed by current sheet scattering, whereas the group having K IB ∼ [12, 32] could be formed by the resonant scattering of low-energy protons by the electromagnetic ion-cyclotron (EMIC) waves. The energy dependence of the upper K limit and close proximity of the latter event to the plasmapause locations support this conclusion.We also discuss other reasons why the K ∼ 8 criterion for isotropization may fail to work, as well as a possible relationship between the two scattering mechanisms.

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“…The distinctive feature of the CSS mechanism is a specific energy-latitude dispersion pattern near the equatorward boundary of proton IB, with a sharp isotropic precipitation boundary occurring at higher (lower) latitude for protons having lower (higher) energy. Such dispersions have been previously demonstrated in the magnetosphere (West et al, 1978), at low altitudes (Imhof, et al 1977(Imhof, et al , 1979Sergeev et al, 2012;Yue et al, 2013) and at middle altitudes (a few R e ) (e.g., Ganushkina et al, 2005). This forms the basic frame of energy-latitude dispersion, which does not change between quiet and disturbed conditions (see, e.g., Fig.…”

Section: Discussionmentioning

confidence: 91%

“…In the Earth's magnetosphere, for the protons with energies of a few keV to hundreds of keV, the boundary between adiabatic and non-adiabatic particle motion is located near the center of the tail current sheet on the nightside at r ∼ 6-9 R e (e.g., Sergeev and Tsyganenko, 1982;Yue et al, 2014). This mechanism (later referred to as the current sheet scattering, or CSS-related) is rather well investigated: it is now widely recognized as the main mechanism which causes the nearly isotropic proton angular distributions in the tail plasma sheet (e.g., Ganushkina et al, 2005;Wang et al, 2012; and which provides the extended proton precipitation into the auroral oval (Donovan et al, 2003;Meurant et al, 2007). In the ionosphere, the distinctive signature of the CSS mechanism is the energy-dispersed equatorward…”

Section: Introductionmentioning

confidence: 99%

Energy–latitude dispersion patterns near the isotropy boundaries of energetic protons

et al. 2015

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Abstract. Non-adiabatic motion of plasma sheet protons causes pitch-angle scattering and isotropic precipitation to the ionosphere, which forms the proton auroral oval. This mechanism related to current sheet scattering (CSS) provides a specific energy-latitude dispersion pattern near the equatorward boundary of proton isotropic precipitation (isotropy boundary, IB), with precipitation sharply decreasing at higher (lower) latitude for protons with lower (higher) energy. However, this boundary maps to the inner magnetosphere, where wave-induced scattering may provide different dispersion patterns as recently demonstrated by . Motivated by the potential usage of the IBs for the magnetotail monitoring as well as by the need to better understand the mechanisms forming the proton IB, we investigate statistically the details of particle flux patterns near the proton IB using NOAA-POES polar spacecraft observations made during September 2009. By comparing precipitatedto-trapped flux ratio (J 0 /J 90 ) at >30 and >80 keV proton energies, we found a relatively small number of simple CSStype dispersion events (only 31 %). The clear reversed (waveinduced) dispersion patterns were very rare (5 %). The most frequent pattern had nearly coinciding IBs at two energies (63 %). The structured precipitation with multiple IBs was very frequent (60 %), that is, with two or more significant J 0 /J 90 dropouts. The average latitudinal width of multiple IB structures was about 1 • . Investigation of dozens of paired auroral zone crossings of POES satellites showed that the IB pattern is stable on a timescale of less than 2 min (a few proton bounce periods) but can evolve on a longer (several minutes) scale, suggesting temporal changes in some mesoscale structures in the equatorial magnetosphere.We discuss the possible role of CSS-related and waveinduced mechanisms and their possible coupling to interpret the emerging complicated patterns of proton isotropy boundaries.

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

Cited by 28 publications

References 29 publications

The Role of Current Sheet Scattering in the Proton Isotropic Boundary Formation During Geomagnetic Storms

The Role of Current Sheet Scattering in the Proton Isotropic Boundary Formation During Geomagnetic Storms

Magnetospheric conditions near the equatorial footpoints of proton isotropy boundaries

Energy–latitude dispersion patterns near the isotropy boundaries of energetic protons

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