On the behavior of O<sup>+5</sup> in coronal holes: Importance of sunward propagating waves

Hollweg, Joseph V.

doi:10.1029/2006ja011917

Cited by 10 publications

(4 citation statements)

References 33 publications

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“…3 indicates the UVCS data from Kohl et al (1998); values of V ⊥ for particles resonating with outgoing waves do not resemble the data at all, while particles resonating with inward waves show a better match. Hollweg (2006c) also finds that the observed behavior of the bulk flow speed of O +5 is better explained by interactions with ingoing waves. Detailed modeling of the ion resonances will have to carefully consider the mix of sunward-propagating and antisunward-propagating waves.…”

Section: The Ion-cyclotron Resonancementioning

confidence: 86%

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The solar wind: Our current understanding and how we got here

Hollweg

2008

J Astrophys Astron

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In the original theory for the solar wind, the electron pressure gradient was the principal accelerating force. This was soon recognized to be insufficient to drive the high-speed streams. Subsequently, the discovery of Alfvén waves in the solar wind led to a long series of models in which wave pressure provided additional acceleration, but these wavedriven models ultimately failed to explain the rapid acceleration of the fast wind close to the Sun. An alternate view was that the pressure of hot protons close to the Sun could explain the rapid acceleration, with the proton heating coming from the cyclotron resonance. SOHO has provided remarkable data which have verified some of the predictions of this view, and given impetus to ongoing studies of the ion-cyclotron resonance in the fast wind. After a historical review, we discuss the basic ideas behind current research, emphasizing the importance of particle kinetics. We conclude with some guesses as to how work might proceed in the future.

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Section: The Ion-cyclotron Resonancementioning

confidence: 86%

“…The efficacy of this idea has been illustrated in a simple "proof of principle" model of the acceleration of O +5 in a coronal hole (Hollweg 2006c). In Fig.…”

Section: The Ion-cyclotron Resonancementioning

confidence: 98%

The solar wind: Our current understanding and how we got here

Hollweg

2008

J Astrophys Astron

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“…The line widths of the Lyα, O VI, and Mg X ultraviolet lines measured in coronal holes by UVCS imply kinetic temperatures of the heavier ions that are more than mass-proportional; T O > 16T p and T Mg > 24T p (Kohl et al 1997;Cranmer et al 1999). This requires strong preferential heating of oxygen and magnesium, which is usually attributed to absorption of wave energy at the cyclotron resonant frequencies as the turbulent cascade transfers energy to small scales and high frequencies (Cranmer et al 1999;Hollweg 2006), though it could also be explained by stochastic heating by lower-frequency waves (Chandran et al 2010). A cyclotron resonance heating process might also explain the factor of 100 variation in the 3 He/ 4 He ratio over the course of a Carrington rotation reported by Gloeckler et al (2016).…”

Section: Dissipation Of Alfvénic Wavesmentioning

confidence: 99%

Dropouts of Fully Stripped Ions in the Solar Wind: A Diagnostic for Wave Heating versus Reconnection

Raymond

Asgari-Targhi

Wilson

et al. 2022

ApJ

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The SWICS instrument on board the ACE satellite has detected frequent intervals in the slow solar wind and interplanetary coronal mass ejections in which C6+ and other fully stripped ions are strongly depleted, though the ionization states of elements such as Si and Fe indicate that those ions should be present. It has been suggested that these “outlier” or “dropout” events can be explained by the resonant cyclotron heating process, because these ions all have the same cyclotron frequency as He2+. We investigate the region in the corona where these outlier events form. It must be above the ionization freeze-in height and the transition to collisionless plasma conditions, but low enough that the wind still feels the effects of solar gravity. We suggest that the dropout events correspond to relatively dense blobs of gas in which the heating is reduced because local variations in the Alfvén speed change the reflection of Alfvén waves and the turbulent cascade. As a result, the wave power at the cyclotron frequency of the fully stripped ions is absorbed by He2+ and may not be able to heat the other fully stripped ions enough to overcome solar gravity. If this picture is borne out, it may help to discriminate between resonant cyclotron heating and stochastic heating models of the solar wind.

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“…The whistler wave spectrum is set up as a power law, B ω ∝ ω −α , and the index α is set to 1.3. The total wave power is chosen in such a way that the total energy content of the full spectrum, from the 5-min oscillations up to the electron cyclotron frequency, corresponds to a wave energy flux density of 275 Wm −2 (Hollweg 2006). The waves propagate into the loop, and the evolution of the wave spectrum due to the spatial variation of the phase speed and the absorption by electrons are considered in the model.…”

Section: Coronal Loop Background Modelmentioning

confidence: 99%

Formation of suprathermal electron distributions in the quiet solar corona

Vocks¹,

Mann²,

Rausche³

2008

A&A

104

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Context. Solar wind electron velocity distribution functions (VDFs) show enhanced levels of suprathermal electrons as compared to a Maxwellian distribution. Previous studies show that the suprathermal tails of solar wind VDFs can be fitted by kappa distributions, and that a coronal origin of the suprathermal electrons is possible. Aims. The generation of suprathermal electrons by resonant interaction with whistler waves in the corona is investigated under quiet solar conditions without any flare activity. The magnetic field geometry is that of a closed magnetic loop. The electron-whistler interaction is described within the framework of quasilinear theory, that leads to pitch-angle diffusion of the electrons in the reference frame of the waves. Methods. A study of electron VDFs requires a kinetic description of the electrons. The model used in this paper is based on a numerical solution of the Boltzmann-Vlasov equation for the electrons, considering Coulomb collisions and wave-electron interaction. The waves are assumed to enter the simulation box with a given power-law spectrum, which evolves inside the box due to wave propagation and absorption by the electrons. Starting from a nearly Maxwellian initial electron VDF, the temporal evolution of the VDF is calculated until a final steady state has been reached. Results. The results show that a population of suprathermal electrons develops in a closed coronal loop. The electron VDF can be approximated by a power-law in the energy range of 4-10 keV. The power-law index is in agreement with the solar wind observations. For lower energy, the electrons are thermalized in the dense model coronal loop, and the efficiency of the acceleration mechanism decreases for higher energies. The energy range of the simulation box has to be chosen sufficiently large, and the influence of the loop geometry on the results is also studied. Conclusions. These numerical studies show that the quiet solar corona is capable of producing suprathermal electron VDFs with similar characteristics to those observed in the solar wind. This study is focused on a closed region in the solar corona, but if such an electron population is present in the corona, it should also appear in the solar wind.

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On the behavior of O⁺⁵ in coronal holes: Importance of sunward propagating waves

Cited by 10 publications

References 33 publications

The solar wind: Our current understanding and how we got here

The solar wind: Our current understanding and how we got here

Dropouts of Fully Stripped Ions in the Solar Wind: A Diagnostic for Wave Heating versus Reconnection

Formation of suprathermal electron distributions in the quiet solar corona

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On the behavior of O+5 in coronal holes: Importance of sunward propagating waves

Cited by 10 publications

References 33 publications

The solar wind: Our current understanding and how we got here

The solar wind: Our current understanding and how we got here

Dropouts of Fully Stripped Ions in the Solar Wind: A Diagnostic for Wave Heating versus Reconnection

Formation of suprathermal electron distributions in the quiet solar corona

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Product

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On the behavior of O⁺⁵ in coronal holes: Importance of sunward propagating waves