The Helium Abundance in Polar Coronal Holes and the Fast Solar Wind

Byhring, Hanne Sigrun

doi:10.1088/0004-637x/738/2/172

Cited by 8 publications

(7 citation statements)

References 31 publications

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“…However, many processes might cause differential flows even between ions of the same element, and their effects on the frozen-in wind charge states can be important (Ko et al 1998). Byhring et al (2011) found that differential flows could account for the intensity enhancement of several lines from key Fe ions in the visible corona measured by Habbal et al (2011); these enhancements could also be present in EUV spectral lines from the same ions. Differential flows affect the use of charge states as diagnostics of the solar corona since different ions respond to the presence of differential flows in a different way (Chen et al 2002).…”

Section: Possible Sources For Disagreement: Plasma Conditionsmentioning

confidence: 99%

Charge State Evolution in the Solar Wind. Iii. Model Comparison With Observations

Landi

Oran

Lepri

et al. 2014

ApJ

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We test three theoretical models of the fast solar wind with a set of remote sensing observations and in-situ measurements taken during the minimum of solar cycle 23. First, the model electron density and temperature are compared to SOHO/SUMER spectroscopic measurements. Second, the model electron density, temperature, and wind speed are used to predict the charge state evolution of the wind plasma from the source regions to the freeze-in point. Frozen-in charge states are compared with Ulysses/SWICS measurements at 1 AU, while charge states close to the Sun are combined with the CHIANTI spectral code to calculate the intensities of selected spectral lines, to be compared with SOHO/SUMER observations in the north polar coronal hole. We find that none of the theoretical models are able to completely reproduce all observations; namely, all of them underestimate the charge state distribution of the solar wind everywhere, although the levels of disagreement vary from model to model. We discuss possible causes of the disagreement, namely, uncertainties in the calculation of the charge state evolution and of line intensities, in the atomic data, and in the assumptions on the wind plasma conditions. Last, we discuss the scenario where the wind is accelerated from a region located in the solar corona rather than in the chromosphere as assumed in the three theoretical models, and find that a wind originating from the corona is in much closer agreement with observations.

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Section: Possible Sources For Disagreement: Plasma Conditionsmentioning

confidence: 99%

Charge State Evolution in the Solar Wind. Iii. Model Comparison With Observations

Landi

Oran

Lepri

et al. 2014

ApJ

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“…But this reliance on diffusion places a limit on the speed with which abundance modification may take place. There are some newer models (Pucci et al, 2010) investigating the changes in abundances with hydrogen flux through a chromospheric magnetic funnel, but this requires significant fine tuning for each element (Pucci et al, 2010, consider O, Ne, and Fe), and appears unlikely to be able to get every element right at the same time, even if the atmosphere was sufficiently quiescent (see also Byhring et al, 2011;Byhring, 2011). Bøet al (2013) make the point that above the chromospheric temperature minimum, the atmosphere is convectively stable, but ignore the fact that waves from the convectively unstable regions may continue to propagate upwards to perturb higher altitudes, as in e.g.…”

Section: Diffusion Models and Variationsmentioning

confidence: 99%

The FIP and Inverse FIP Effects in Solar and Stellar Coronae

Laming

2015

Living Rev. Sol. Phys.

287

304

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We review our state of knowledge of coronal element abundance anomalies in the Sun and stars. We concentrate on the first ionization potential (FIP) effect observed in the solar corona and slow-speed wind, and in the coronae of solar-like dwarf stars, and the "inverse FIP" effect seen in the corona of stars of later spectral type; specifically M dwarfs. These effects relate to the enhancement or depletion, respectively, in coronal abundance with respect to photospheric values of elements with FIP below about 10~eV. They are interpreted in terms of the ponderomotive force due to the propagation and/or reflection of magnetohydrodynamic waves in the chromosphere. This acts on chromospheric ions, but not neutrals, and so can lead to ion-neutral fractionation. A detailed description of the model applied to closed magnetic loops, and to open field regions is given, accounting for the observed difference in solar FIP fractionation between the slow and fast wind. It is shown that such a model can also account for the observed depletion of helium in the solar wind. The helium depletion is sensitive to the chromospheric altitude where ion-neutral separation occurs, and the behavior of the helium abundance in the closed magnetic loop strongly suggests that the waves have a coronal origin. This, and other similar inferences may be expected to have a strong bearing on theories of solar coronal heating. Chromospheric waves originating from below as acoustic waves mode convert, mainly to fast mode waves, can also give rise to ion-neutral separation. Depending on the geometry of the magnetic field, this can result in FIP or Inverse FIP effects. We argue that such configurations are more likely to occur in later-type stars (known to have stronger field in any case), and that this explains the occurrence of the Inverse FIP effect in M dwarfs.Comment: Review paper submitted to Living Reviews in Solar Physics. 74 pages. Some material revised and updated from astro-ph/0405230, arXiv:0901.3350, arXiv:1110.435

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“…For example, it has been shown that the solar wind speed squared is inversely proportional to the loop temperature (Fisk 2003;Gloeckler, Zurbuchen & Geiss 2003) and that hotter loops are typically larger (Feldman, Widing & Warren 1999). Rakowski & Laming (2012) showed that in larger loops the first ionization potential effect (Laming 2004) causes more helium depletion than in shorter loops, and argued that gravitational settling (Byhring 2011) is too slow to cause the variability seen. Combining these results suggests that slow solar wind originates from reconnection between open field and large, hot loops with depleted amounts of α-particles.…”

Section: Low α-Particle Abundancementioning

confidence: 99%

Plasma properties, switchback patches, and low α-particle abundance in slow Alfvénic coronal hole wind at 0.13 au

Woolley

Matteini

McManus

et al. 2021

Monthly Notices of the Royal Astronomical Society

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The Parker Solar Probe (PSP) mission presents a unique opportunity to study the near-Sun solar wind closer than any previous spacecraft. During its fourth and fifth solar encounters, PSP had the same orbital trajectory, meaning that solar wind was measured at the same latitudes and radial distances. We identify two streams measured at the same heliocentric distance (∼0.13au) and latitude (∼-3.5○) across these encounters to reduce spatial evolution effects. By comparing the plasma of each stream, we confirm that they are not dominated by variable transient events, despite PSP’s proximity to the heliospheric current sheet. Both streams are consistent with a previous slow Alfvénic solar wind study once radial effects are considered, and appear to originate at the Southern polar coronal hole boundary. We also show that the switchback properties are not distinctly different between these two streams. Low α-particle abundance (∼ 0.6 %) is observed in the encounter 5 stream, suggesting that some physical mechanism must act on coronal hole boundary wind to cause α-particle depletion. Possible explanations for our observations are discussed, but it remains unclear whether the depletion occurs during the release or the acceleration of the wind. Using a flux tube argument, we note that an α-particle abundance of ∼ 0.6 % in this low velocity wind could correspond to an abundance of ∼ 0.9 % at 1 au. Finally, as the two streams roughly correspond to the spatial extent of a switchback patch, we suggest that patches are distinct features of coronal hole wind.

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The Helium Abundance in Polar Coronal Holes and the Fast Solar Wind

Cited by 8 publications

References 31 publications

Charge State Evolution in the Solar Wind. Iii. Model Comparison With Observations

Charge State Evolution in the Solar Wind. Iii. Model Comparison With Observations

The FIP and Inverse FIP Effects in Solar and Stellar Coronae

Plasma properties, switchback patches, and low α-particle abundance in slow Alfvénic coronal hole wind at 0.13 au

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