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Raymond, J. C.; Kohl, J. L.; Noci, G.; Antonucci, E.; Tondello, G.; Huber, M. C. E.; Gardner, L. D.; Nicolosi, P.; Fineschi, Silvano; Romoli, M.; Spadaro, D.; Siegmund, O. H. W.; Benna, C.; Ciaravella, A.; Cranmer, Steven R.; Giordano, S.; Karovska, M.; Martin, R.; Michels, J.; Modigliani, A.; Naletto, G.; Panasyuk, A. V.; Pernechele, Claudio; Poletto, G.; Smith, Peter L.; Suleiman, R. M.; Strachan, L.

doi:10.1023/a:1004948423169

Cited by 252 publications

(185 citation statements)

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“…Both the radial profiles of T e and H i T ⊥ exhibit a slight decrease, practically overlapping between 2.5 and 3.3 R and then only slightly diverging at greater heliocentric distances. This agrees with the hypothesis of thermal equilibrium between electrons and hydrogen atoms (protons), suggested on the basis of the high-density and low-outflow conditions characterizing streamers, expecially at low heights (cf., Raymond et al 1997;Vásquez et al 2003). …”

Section: Diagnostics Of Physical Parametersmentioning

confidence: 99%

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Physical parameters of a mid-latitude streamer during the declining phase of the solar cycle

Spadaro

Susino

Ventura

et al. 2007

A&A

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Context. Investigating the physical properties of solar coronal streamers is important for understanding their role in the global magnetic structure of the extended solar atmosphere, as well as in the generation of the slow solar wind. Aims. We hope to contribute as completely as possible to the ongoing SOHO instruments campaign devoted to the study of the physical characteristics of coronal streamers at various heliocentric distances. Results. Electron densities and temperatures, H i and O vi kinetic temperatures, and outflow velocities were derived from the line intensities and widths, as well as from the O vi line intensity ratio in the 1.6−5 R range of heights, limited to the central region of the streamer. To our knowledge, the H i outflow velocities obtained in this work are the first ones determined inside a streamer structure. They are significantly lower than those of the O vi ions. This, together with the O vi kinetic temperatures that are much higher than the H i ones, suggest that the absorption of Alfvén waves at the ion cyclotron frequency might also occur inside streamers. Methods. We analyzed ultraviolet H iConclusions. In comparison with other streamers described in the literature, the structure examined in this work generally exhibits lower electron density and neutral hydrogen kinetic temperature. Conversely, the O vi kinetic temperature and outflow velocity radial profiles are consistent with the results for the other examined streamers.

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Section: Diagnostics Of Physical Parametersmentioning

confidence: 99%

“…Many recent works have focused on this topic (e.g., Marsch 1997;Noci et al 1997;Raymond et al 1997;Habbal et al 1997;Woo & Martin 1997), but -at present -a firm identification of the slow wind-source regions inside streamers is still an unresolved issue.…”

Section: Introductionmentioning

confidence: 99%

Physical parameters of a mid-latitude streamer during the declining phase of the solar cycle

Spadaro

Susino

Ventura

et al. 2007

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“…According to Gabriel et al (1971), the dominant excitation mechanism is almost exclusively caused by the resonant photo-excitation of coronal neutral hydrogen by the chromospherically produced Lα photons. For the Lβ line, there is a slightly dominant contribution from collisional excitations relative to photo-excitations, which in contrast for the Lγ line by far dominates (see Table 4 of Raymond et al 1997). Only in the case of photo-excitation can the scattered radiation become linearly polarised.…”

Section: Resultsmentioning

confidence: 99%

“…2a and 6a of their paper. The profiles and intensities of the chromospheric Lα and Lβ lines are taken from Lemaire et al (2005), while the Lγ line profile is assumed to be equal to that of the Lβ line with the difference in peak intensity taken from Raymond et al (1997). These lines are all formed by doublets at almost the same wavelength, and each doublet has the same lifetime, but, as already mentioned, only the J u = 3/2 → J = 1/2 transition can be linearly polarised in resonance scattering.…”

Section: Resultsmentioning

confidence: 99%

“…4, we "turned off" both the magnetic field and solar wind and show the effect of active regions on the solar surface by placing eight active regions symmetrically on both hemispheres at latitudes of ±π/4 and longitudes (measured from the plane of the sky) of 0, π/2, π, and 3π/2, respectively, reflecting more or less the starting configuration of activity at the beginning of the solar cycle. The values for the intensity contrast were taken from Raymond et al (1997), and the active regions are all assumed to have the same diameter of 30 000 km. We find rotations that locally attain values of the same order of magnitude as those found for magnetic fields and the solar wind, i.e.…”

Section: Resultsmentioning

confidence: 99%

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Spectropolarimetric forward modelling of the lines of the Lyman-series using a self-consistent, global, solar coronal model

Khan

Belluzzi

Degl’Innocenti

et al. 2011

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Context. The presence and importance of the coronal magnetic field is illustrated by a wide range of phenomena, such as the abnormally high temperatures of the coronal plasma, the existence of a slow and fast solar wind, the triggering of explosive events such as flares and CMEs. Aims. We investigate the possibility of using the Hanle effect to diagnose the coronal magnetic field by analysing its influence on the linear polarisation, i.e. the rotation of the plane of polarisation and depolarisation. Methods. We analyse the polarisation characteristics of the first three lines of the hydrogen Lyman-series using an axisymmetric, self-consistent, minimum-corona MHD model with relatively low values of the magnetic field (a few Gauss). Results. We find that the Hanle effect in the above-mentioned lines indeed seems to be a valuable tool for analysing the coronal magnetic field. However, great care must be taken when analysing the spectropolarimetry of the Lα line, given that a non-radial solar wind and active regions on the solar disk can mimic the effects of the magnetic field, and, in some cases, even mask them. Similar drawbacks are not found for the Lβ and Lγ lines because they are more sensitive to the magnetic field. We also briefly consider the instrumental requirements needed to perform polarimetric observations for diagnosing the coronal magnetic fields. Conclusions. The combined analysis of the three aforementioned lines could provide an important step towards better constrainting the value of solar coronal magnetic fields.

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Two‐dimensional hybrid models of H⁺‐He⁺⁺ expanding solar wind plasma heating

2014

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Preferential heating and acceleration of the solar wind He++ ions compared to protons in fast solar wind streams have been known for decades, thanks to in situ spacecraft measurements at 0.29–5 AU. Turbulent magnetic field fluctuations with approximate power law spectra have been observed as well. However, the exact causes of these processes are still not known due to the lack of detailed information on the magnetic field fluctuations and ion velocity distributions in the acceleration region of the solar wind. Here the collisionless heating processes in expanding solar wind plasma are investigated using 2‐D hybrid modeling with parameters appropriate to the heliocentric distance of 10 RS. In this study the ion dynamics is described kinetically, while electrons are treated as a background massless fluid in an expanding solar wind model. The source of free energy for the heating is introduced through an initial nonequilibrium state of the plasma with large He++ ion temperature anisotropy or with super‐Alfvénic relative ion drift. We also employ an externally imposed spectrum of magnetic fluctuations in the frequency range below the proton gyroresonant frequency to heat the He++ ions. We investigate the effects of solar wind radial expansion by modeling several values of the expansion rate in a parametric study. We find that the preferential ion heating is attained in both nonexpanding and expanding solar wind models. Thus, the expansion has little effect on the preferential He++ ion heating by the processes considered here. Moreover, the expansion leads to faster evolution of the magnetosonic drift instability, reducing the drift velocity to lower values sooner, and the corresponding generation of the magnetic fluctuations that heat the ions, compared to the nonexpanding case. This is due to the reduction of the perpendicular particle velocities in the expanding (inflated) frame. For cases with little proton perpendicular heating, the solar wind expansion leads to the reduction of the proton temperature anisotropy to values less than one in the low‐βp∥ solar wind acceleration region consistent with some observed values. However, this effect must be offset by perpendicular proton heating—likely by the same process that heats the He++ ions to be consistent with the full range of observed proton perpendicular temperature values.

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Cited by 252 publications

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Physical parameters of a mid-latitude streamer during the declining phase of the solar cycle

Physical parameters of a mid-latitude streamer during the declining phase of the solar cycle

Spectropolarimetric forward modelling of the lines of the Lyman-series using a self-consistent, global, solar coronal model

Two‐dimensional hybrid models of H⁺‐He⁺⁺ expanding solar wind plasma heating

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Cited by 252 publications

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Physical parameters of a mid-latitude streamer during the declining phase of the solar cycle

Physical parameters of a mid-latitude streamer during the declining phase of the solar cycle

Spectropolarimetric forward modelling of the lines of the Lyman-series using a self-consistent, global, solar coronal model

Two‐dimensional hybrid models of H+‐He++ expanding solar wind plasma heating

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Two‐dimensional hybrid models of H⁺‐He⁺⁺ expanding solar wind plasma heating