Ulysses electron distributions fitted with Kappa functions

Maksimović, M.; Pierrard, V.; Riley, P. J.

doi:10.1029/97gl00992

Cited by 406 publications

(291 citation statements)

References 16 publications

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“…2). This is because the distribution function of solar wind electrons is complex, with a Maxwellian-like core and a halo (elevated wings) approximated by the Maxwellian or kappa-like function (Pilipp et al 1987;Maksimovic et al 1997). The abundance of the halo population relative to the core varies with heliocentric distance.…”

Section: Electron Impact Ionizationmentioning

confidence: 99%

Modulation of neutral interstellar He, Ne, O in the heliosphere. Survival probabilities and abundances at IBEX

Bzowski

Sokół

Kubiak

et al. 2013

A&A

111

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Context. Direct sampling of neutral interstellar (NIS) atoms by the Interstellar Boundary Explorer (IBEX) can potentially provide a complementary method for studying element abundances in the Local Interstellar Cloud (LIC) and processes in the heliosphere interface. Aims. We set the stage for abundance-aimed in-depth analysis of measurements of NIS He, Ne, and O by IBEX and determine systematic differences between abundances derived from various calculation methods and their uncertainties.Methods. Using a model of ionization rates of the NIS species in the heliosphere, based on independent measurements of the solar wind and solar EUV radiation, we developed a time-dependent method of calculating the survival probabilities of NIS atoms from the termination shock (TS) of the solar wind to IBEX. With them, we calculated densities of these species along the Earth's orbit and simulated the fluxes of NIS species as observed by IBEX. We studied pairwise ratios of survival probabilities, densities, and fluxes of NIS species at IBEX to calculate correction factors for inferring the abundances at TS. Results. The analytic method of calculating the survival probabilities gives acceptable results only for He and Ne during low solar activity. For the remaining portions of the solar cycle, and at all times for O, a fully time-dependent model should be used. Electronimpact ionization is surprisingly important for NIS O. Interpreting the IBEX observations using the time-dependent model yields the LIC Ne/O abundance of 0.16 ± 40%. The uncertainty is mostly due to uncertainties in the ionization rates and in the NIS gas flow vector. Conclusions. The Ne/He, O/He, and Ne/O ratios for survival probabilities, local densities, and fluxes scaled to TS systematically differ and thus an analysis based only on survival probabilities or densities is not recommended, except the Ne/O abundance for observations at low solar activity.

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Section: Electron Impact Ionizationmentioning

confidence: 99%

Modulation of neutral interstellar He, Ne, O in the heliosphere. Survival probabilities and abundances at IBEX

Bzowski

Sokół

Kubiak

et al. 2013

A&A

111

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“…1 appears to follow the notation of Maksimovic et al, 51 a paper cited in the Response to our Comment. However, the latter paper does not define T in the form given in Ref.…”

Section: ͑13͒mentioning

confidence: 99%

Comment on “Mathematical and physical aspects of Kappa velocity distribution” [Phys. Plasmas 14, 110702 (2007)]

Hellberg¹,

Mace²,

Baluku³

et al. 2009

Physics of Plasmas

354

240

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A recent paper [L.-N. Hau and W.-Z. Fu, Phys. Plasmas 14, 110702 (2007)] deals with certain mathematical and physical properties of the kappa distribution. We comment on the authors’ use of a form of distribution function that is different from the “standard” form of the kappa distribution, and hence their results, inter alia for an expansion of the distribution function and for the associated number density in an electrostatic potential, do not fully reflect the dependence on κ that would be associated with the conventional kappa distribution. We note that their definition of the kappa distribution function is also different from a modified distribution based on the notion of nonextensive entropy.

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“…Scudder & Olbert (1979) first suggested that the solar wind expansion combined with reduced Coulomb collisions for suprathermal electrons can give rise to nonthermal electron populations. Following Scudderʼs work, Maksimovic et al (1997a) developed a kinetic model of solar wind that is based on Kappa distributions for electrons and protons escaping from the corona, and this model is supported by the observed anticorrelation between the solar wind speed and the fitted κ index of halo electrons (Maksimovic et al 1997b). Vocks et al (2005) suggested that the resonant interactions between antisunward-travelling suprathermal electrons and sunwardpropagating whistler waves are capable of significantly pitchangle (PA) scattering suprathermal electrons, leading to the formation of the halo/strahl as observed in the IPM.…”

Section: Introductionmentioning

confidence: 99%

QUIET-TIME SUPRATHERMAL (∼0.1–1.5 keV) ELECTRONS IN THE SOLAR WIND

Tao

Wang

Zong

et al. 2016

ApJ

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We present a statistical survey of the energy spectrum of solar wind suprathermal (∼0.1-1.5 keV) electrons measured by the WIND3DP instrument at 1 AU during quiet times at the minimum and maximum of solar cycles 23 and 24. After separating (beaming) strahl electrons from (isotropic) halo electrons according to their different behaviors in the angular distribution, we fit the observed energy spectrum of both strahl and halo electrons at ∼0.1-1.5 keV to a Kappa distribution function with an index κ and effective temperature T eff . We also calculate the number density n and average energy E avg of strahl and halo electrons by integrating the electron measurements between ∼0.1 and 1.5 keV. We find a strong positive correlation between κ and T eff for both strahl and halo electrons, and a strong positive correlation between the strahl n and halo n, likely reflecting the nature of the generation of these suprathermal electrons. In both solar cycles, κ is larger at solar minimum than at solar maximum for both strahl and halo electrons. The halo κ is generally smaller than the strahl κ (except during the solar minimum of cycle 23). The strahl n is larger at solar maximum, but the halo n shows no difference between solar minimum and maximum. Both the strahl n and halo n have no clear association with the solar wind core population, but the density ratio between the strahl and halo roughly anti-correlates (correlates) with the solar wind density (velocity).

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Ulysses electron distributions fitted with Kappa functions

Cited by 406 publications

References 16 publications

Modulation of neutral interstellar He, Ne, O in the heliosphere. Survival probabilities and abundances at IBEX

Modulation of neutral interstellar He, Ne, O in the heliosphere. Survival probabilities and abundances at IBEX

Comment on “Mathematical and physical aspects of Kappa velocity distribution” [Phys. Plasmas 14, 110702 (2007)]

QUIET-TIME SUPRATHERMAL (∼0.1–1.5 keV) ELECTRONS IN THE SOLAR WIND

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