L’impossible ambassade

Boland, André

doi:10.4000/books.pusl.10014

Cited by 6 publications

(7 citation statements)

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“…If the Doppler shifts represent a steady flow, then a velocity of even a few kilometers per second produces an enthalpy flux that is comparable to the energy transported by thermal conduction in these layers (e.g., Pneuman & Kopp 1978). Similarly, the nonthermal line broadening and its behavior as a function of temperature may hold clues to energy transport by magnetohydrodynamic waves (e.g., Boland et al 1975;Mariska 1992).…”

Section: Introductionmentioning

confidence: 98%

Doppler Shifts and Nonthermal Broadening in the Quiet Solar Transition Region: O [CSC]vi[/CSC] [CLC][/CLC]

Warren

Mariska

Wilhelm

et al. 1997

The Astrophysical Journal

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Using observations from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) experiment flown on the Solar and Heliospheric Observatory (SOHO) spacecraft, we have measured Doppler wavelength shifts and nonthermal broadening in the 1032 and 1038 Å emission lines of O VI and the 1036 and 1037 Å emission lines of C II. Near Sun center the C II lines exhibit an average redshift of 2 H 3 km s Ϫ1 , consistent with earlier observations in this temperature range. The O VI emission lines exhibit average Doppler velocities of 5 H 3 km s Ϫ1 , suggesting the presence of redshifted material at 2.9 ϫ 10 5 K. For the O VI lines, the average nonthermal component of the observed line width is 34 H 3 km s Ϫ1 .

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Section: Introductionmentioning

confidence: 98%

Doppler Shifts and Nonthermal Broadening in the Quiet Solar Transition Region: O [CSC]vi[/CSC] [CLC][/CLC]

Warren

Mariska

Wilhelm

et al. 1997

The Astrophysical Journal

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“…The observed intensity oscillations in coronal emission lines and continuum have been interpreted in terms of the existence of coronal waves, which are thought to be responsible for the heating of coronal plasma ( Tsubaki 1977;Koutchmy et al 1983;Pasachoff & Ladd 1987;Domingo et al 1995;Singh et al 1997;Schrijver et al 1999;Roberts 2000;Sakurai et al 2002;Minarovjech et al 2003). The widths of emission lines formed in the transition and coronal regions are greater than those expected from the thermal broadening due to the high temperature of the solar corona (e.g., Boland et al 1973Boland et al , 1975Doschek et al 1976;Shine et al 1976;Kjeldseth Moe & Nicolas 1977;Singh et al 1982). The observed excess line width has been attributed to the existence of nonthermal broadening due to turbulence or waves in the corona.…”

Section: Introductionmentioning

confidence: 99%

Do the Line Widths of Coronal Emission Lines Increase with Height above the Limb?

Singh

Sakurai

Ichimoto

2006

ApJ

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In our earlier studies we obtained off-the-limb spectroscopic observations in a number of forbidden emission lines ([ Fe x-xiv]) to study the physical properties and their temporal variations in steady coronal structures. Short exposure times adopted in those observations permitted us to study the variation in line widths up to about 150 00 above the limb. With a view to investigating the variations in the parameters of coronal emission lines up to about 500 00 , we made raster scans with exposure times that are longer than the earlier exposure times by a factor of about 10. We find that the FWHM of the [Fe xiv] 5303 8 line decreases up to 300 00 AE 50 00 and then remains more or less the same up to 500 00 , while that of the [ Fe x] 6374 8 line increases up to about 250 00 and subsequently remains unchanged. The FWHMs of the [Fe xi] 7892 8 and [ Fe xiii] 10747 8 lines show an intermediate behavior. Furthermore, the ratio of the FWHM of 6374 to 5303 8 increases from 0.93 at the limb to 1.18 at 200 00 above the limb. The nonvariability in the FWHM of emission lines after about 300 00 above the limb in steady coronal structures does not support the prevailing view that the nonthermal velocity increases with height due to either the coronal waves or the high-velocity solar wind. The present results indicate the inadequacy of the earlier coronal loop models. The observed variations in FWHM of the coronal emission lines with height above the limb can be explained by assuming the recent model of coronal loops proposed by Akiyama et al.

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“…The origin of excess optically thin spectral line widths beyond their thermal Doppler widths is unclear. Since a rocket flight analyzed by Boland et al (1975), it has been known that spectral lines from ions present in the solar transition region and corona have wider profiles than those expected from pure thermal Doppler broadening alone, based on the ionization equilibrium temperatures at which they are formed. The profiles of the majority of the lines are Gaussian or close to Gaussian, and the excess broadening does not appear to be a strong function of position on the solar disk.…”

Section: Introductionmentioning

confidence: 99%

Flows and Nonthermal Velocities in Solar Active Regions Observed with the EUV Imaging Spectrometer onHinode: A Tracer of Active Region Sources of Heliospheric Magnetic Fields?

Doschek¹,

Warren²,

Mariska³

et al. 2008

Astrophysical Journal

148

132

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From Doppler velocity maps of active regions constructed from spectra obtained by the EUV Imaging Spectrometer (EIS) on the Hinode spacecraft we observe large areas of outflow (20Y50 km s À1 ) that can persist for at least a day. These outflows occur in areas of active regions that are faint in coronal spectral lines formed at typical quietSun and active region temperatures. The outflows are positively correlated with nonthermal velocities in coronal plasmas. The bulk mass motions and nonthermal velocities are derived from spectral line centroids and line widths, mostly from a strong line of Fe xii at 195.12 8. The electron temperature of the outflow regions estimated from an Fe xiii to Fe xii line intensity ratio is about (1:2Y1:4) ; 10 6 K. The electron density of the outflow regions derived from a density-sensitive intensity ratio of Fe xii lines is rather low for an active region. Most regions average around 7 ; 10 8 cm À3 , but there are variations on pixel spatial scales of about a factor of 4. We discuss results in detail for two active regions observed by EIS. Images of active regions in line intensity, line width, and line centroid are obtained by rastering the regions. We also discuss data from the active regions obtained from other orbiting spacecraft that support the conclusions obtained from analysis of the EIS spectra. The locations of the flows in the active regions with respect to the longitudinal photospheric magnetic fields suggest that these regions might be tracers of long loops and/or open magnetic fields that extend into the heliosphere, and thus the flows could possibly contribute significantly to the solar wind.

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L’impossible ambassade

Cited by 6 publications

References 0 publications

Doppler Shifts and Nonthermal Broadening in the Quiet Solar Transition Region: O [CSC]vi[/CSC] [CLC][/CLC]

Doppler Shifts and Nonthermal Broadening in the Quiet Solar Transition Region: O [CSC]vi[/CSC] [CLC][/CLC]

Do the Line Widths of Coronal Emission Lines Increase with Height above the Limb?

Flows and Nonthermal Velocities in Solar Active Regions Observed with the EUV Imaging Spectrometer onHinode: A Tracer of Active Region Sources of Heliospheric Magnetic Fields?

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