The polar wind and the terrestrial helium budget

Axford, W. I.

doi:10.1029/ja073i021p06855

Cited by 328 publications

(204 citation statements)

References 32 publications

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“…The classical picture of the polar wind is as an ambipolar flow in which H + and He + escape the Earth's gravity at supersonic speeds but the heavier O + does not [Axford, 1968;Banks and Holzer, 1968, 1969a, 1969b. The nonclassical polar wind includes other energization processes which can accelerate O + to escape energies and create nonthermal ion beams and conics (see Yau and André [1997], André and Yau [1997] Moore et al [1999], and Yau et al [2011] for reviews).…”

Section: Introductionmentioning

confidence: 99%

Heating of the sunlit polar cap ionosphere by reflected photoelectrons

2014

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Photoelectrons escape from the ionosphere on sunlit polar cap field lines. In order for those field lines to carry zero current without significant heavy ion outflow or cold electron inflow, field-aligned potential drops must form to reflect a portion of the escaping photoelectron population back to the ionosphere. Using a 1-D ionosphere-polar wind model and measurements from the Resolute Bay Incoherent Scatter Radar (RISR-N), this paper shows that these reflected photoelectrons are a significant source of heat for the sunlit polar cap ionosphere. The model includes a kinetic suprathermal electron transport solver, and it allows energy input from the upper boundary in three different ways: thermal conduction, soft precipitation, and potentials that reflect photoelectrons. The simulations confirm that reflection potentials of several tens of eV are required to prevent cold electron inflow and demonstrate that the flux tube integrated change in electron heating rate (FTICEHR) associated with reflected photoelectrons can reach 10 9 eV cm −2 s −1 . Soft precipitation can produce FTICEHR of comparable magnitudes, but this extra heating is divided among more electrons as a result of electron impact ionization. Simulations with no reflected photoelectrons and with downward field-aligned currents (FAC) primarily carried by the escaping photoelectrons have electron temperatures which are ∼250-500 K lower than the RISR-N measurements in the 300-600 km region; however, simulations with reflected photoelectrons, zero FAC, and no other form of heat flux through the upper boundary can satisfactorily reproduce the RISR-N data.

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Section: Introductionmentioning

confidence: 99%

Heating of the sunlit polar cap ionosphere by reflected photoelectrons

2014

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“…Axford [1968] argued that the outflow of plasma should be supersonic and referred to it as the "polar wind" in analogy to the solar wind. A simple hydrodynamic description predicted supersonic ion outflow at times compared to the ion transport times [Wilson, 1995;Hoet al,, 1997].…”

Section: Introductionmentioning

confidence: 99%

Self‐consistent simulation of the photoelectron‐driven polar wind from 120 km to 9 R_E altitude

Su¹,

Horwitz²,

Wilson³

et al. 1998

J. Geophys. Res.

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“…Because the polar wind (as termed in analogy with the solar wind (Axford 1968;Banks & Holzer 1968) is also an example of plasma outflow along open magnetic field lines, our present model retains the general features of the self-consistent hybrid model: it is based on an iterative scheme between fluid and kinetic calculations. In the fluid calculations, a set of equations determines the ambipolar electric field and the properties of the bulk thermal electrons, whose distributions are assumed to be in a drifting Maxwellian.…”

Section: Modelmentioning

confidence: 98%

Comparison of the effects of wave-particle interactions and the kinetic suprathermal electron population on the acceleration of the solar wind

Tam

Chang

2002

A&A

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Abstract. Kinetic effects due to wave-particle interactions and suprathermal electrons have been suggested in the literature as possible solar wind acceleration mechanisms. Ion cyclotron resonant heating, in particular, has been associated with some qualitative features observed in the solar wind. In terms of solar wind acceleration, however, it is interesting to compare the kinetic effects of suprathermal electrons with those due to the wave-particle interactions. The combined effects of the two acceleration mechanisms on the fast solar wind have been studied by Tam & Chang (1999a,b). In this study, we investigate the role of the suprathermal electron population in the acceleration of the solar wind. Our model follows the global kinetic evolution of the fast solar wind under the influence of ion cyclotron resonant heating, while taking into account Coulomb collisions, and the ambipolar electric field that is consistent with the particle distributions themselves. The kinetic effects due to the suprathermal electrons, which we define to be the tail of the electron distributions, can be included in the model as an option. By comparing the results with and without the inclusion of the suprathermal electron effects, we determine the relative importance of suprathermal electrons and wave-particle interactions in driving the solar wind. We find that although suprathermal electrons enhance the ambipolar electric potential in the solar wind considerably, their overall influence as an acceleration mechanism is relatively insignificant in a wave-driven solar wind.

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The polar wind and the terrestrial helium budget

Cited by 328 publications

References 32 publications

Heating of the sunlit polar cap ionosphere by reflected photoelectrons

Heating of the sunlit polar cap ionosphere by reflected photoelectrons

Self‐consistent simulation of the photoelectron‐driven polar wind from 120 km to 9 R_E altitude

Comparison of the effects of wave-particle interactions and the kinetic suprathermal electron population on the acceleration of the solar wind

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The polar wind and the terrestrial helium budget

Cited by 328 publications

References 32 publications

Heating of the sunlit polar cap ionosphere by reflected photoelectrons

Heating of the sunlit polar cap ionosphere by reflected photoelectrons

Self‐consistent simulation of the photoelectron‐driven polar wind from 120 km to 9 RE altitude

Comparison of the effects of wave-particle interactions and the kinetic suprathermal electron population on the acceleration of the solar wind

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Self‐consistent simulation of the photoelectron‐driven polar wind from 120 km to 9 R_E altitude