The Physical Conditions in a Polar Coronal Hole and Nearby Regions from Norikura and<i>SOHO</i>Observations

Raju, K. P.; Sakurai, Takashi; Ichimoto, Kiyoshi; Singh, Jagdev

doi:10.1086/317143

Cited by 20 publications

(12 citation statements)

References 37 publications

(46 reference statements)

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“…The results that the line widths are narrower in plumes than in lanes confirm those of Antonucci et al (1997), Hassler et al (1997), Raju et al (2000), and Banerjee et al (2000a), but the difference found is larger than in most earlier studies.…”

Section: Discussionsupporting

confidence: 87%

Solar coronal-hole plasma densities and temperatures

Wilhelm¹

2006

A&A

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Polar plumes extending from the Sun into the solar corona have long been seen during eclipses, and can now be studied without this restriction with telescopes and spectrometers on board of spacecraft. Despite the large amount of observational data available on this prominent phenomenon, it is not clear whether plumes contribute substantially to the fast solar-wind streams emanating from coronal holes. An understanding of the processes leading to the formation of bright plumes and the surrounding darker inter-plume regions in coronal holes requires a good knowledge of the physical conditions in plumes and their environment. This investigation aims at measuring the electron densities and temperatures in these regions with the help of radiance ratios of ultraviolet emission lines obtained by SUMER on SOHO. It finds densities of about 7 × 10 7 cm −3 in bright plumes and 1.3 × 10 7 cm −3 in inter-plume lanes at ≈45 Mm above the limb. At this height, the total plume cross-section relative to the size of the coronal hole was found to be less than 8%. The densities drop by a factor of roughly two over the next 80 Mm in height, in lanes a little less than seen in plumes. In this height range, the electron temperatures in plumes are ≈7.5 × 10 5 K and ≈1.13 × 10 6 K in inter-plume regions. The effective ion temperatures, deduced from the line widths, are higher and nearly independent of the altitude in plumes, whereas they increase in inter-plume regions, starting from an even higher level. No systematic dependence of the line-of-sight bulk velocities on the brightness could be found in the coronal-hole plasma.

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Section: Discussionsupporting

confidence: 87%

Solar coronal-hole plasma densities and temperatures

Wilhelm¹

2006

A&A

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“…Hassler et al (1997), using SUMER data, report a broader line width in interplume regions, with respect to plumes. This result has been confirmed by further studies, from either groundbased coronagraph data (Raju et al, 2000), or from data acquired by space-borne experiments like SUMER (see, e.g., Banerjee et al, 1998Banerjee et al, , 2000b and CDS (see, e.g., Banerjee et al, 2000aBanerjee et al, , 2001O'Shea et al, 2003). A summary of the plume/interplume line widths can be found in Table 2 of Wilhelm (2012).…”

Section: The Plume Effective Temperaturesupporting

confidence: 57%

Solar Coronal Plumes

Poletto

2015

Living Rev. Sol. Phys.

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Polar plumes are thin long ray-like structures that project beyond the limb of the Sun polar regions, maintaining their identity over distances of several solar radii. Plumes have been first observed in white-light (WL) images of the Sun, but, with the advent of the space era, they have been identified also in X-ray and UV wavelengths (XUV) and, possibly, even in in situ data. This review traces the history of plumes, from the time they have been first imaged, to the complex means by which nowadays we attempt to reconstruct their 3-D structure. Spectroscopic techniques allowed us also to infer the physical parameters of plumes and estimate their electron and kinetic temperatures and their densities. However, perhaps the most interesting problem we need to solve is the role they cover in the solar wind origin and acceleration: Does the solar wind emanate from plumes or from the ambient coronal hole wherein they are embedded? Do plumes have a role in solar wind acceleration and mass loading? Answers to these questions are still somewhat ambiguous and theoretical modeling does not provide definite answers either. Recent data, with an unprecedented high spatial and temporal resolution, provide new information on the fine structure of plumes, their temporal evolution and relationship with other transient phenomena that may shed further light on these elusive features. Article RevisionsLiving Reviews supports two ways of keeping its articles up-to-date:Fast-track revision. A fast-track revision provides the author with the opportunity to add short notices of current research results, trends and developments, or important publications to the article. A fast-track revision is refereed by the responsible subject editor. If an article has undergone a fast-track revision, a summary of changes will be listed here.Major update. A major update will include substantial changes and additions and is subject to full external refereeing. It is published with a new publication number.For detailed documentation of an article's evolution, please refer to the history document of the article's online version at http://dx

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“…The high speed solar wind outflows are accelerated very close to the solar surface [62]. The solar wind originates from the coronal holes, which are open magnetic field regions with a temperature of ∼ 1 MK [63] (see also ref. [38]).…”

Section: Related Observationsmentioning

confidence: 99%

Observational evidence for gravitationally trapped massive axion(-like) particles

DiLella

Zioutas

2003

Astroparticle Physics

106

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Several unexpected astrophysical observations can be explained by gravitationally captured massive axions or axion-like particles, which are produced inside the Sun or other stars and are accumulated over cosmic times. Their radiative decay in solar outer space would give rise to a 'self-irradiation' of the whole star, providing the time-independent component of the corona heating source (we do not address here the flaring Sun). In analogy with the Sun-irradiated Earth atmosphere, the temperature and density gradient in the corona−chromosphere transition region is suggestive for an omnipresent irradiation of the Sun, which is the strongest evidence for the generic axion-like scenario. The same mechanism is compatible with phenomena like the solar wind, the X-rays from the dark-side of the Moon, the X-Ray Background Radiation, the diffuse X-ray excesses (below ∼ 1 keV), the non-cooling of oldest Stars, etc. A temperature of ∼ 10 6 K is observed in various places, while the radiative decay of a population of such elusive particles mimics a hot gas, which fits unexpected astrophysical X-ray observations. Furthermore, the recently reconstructed quiet solar X-ray spectrum during solar minimum supports this work, since it covers the expected energy range, and it is consistent with the result of a simulation based on Kaluza-Klein axions above ∼ 1 keV. The derived axion luminosity (L a ≈ 0.16L ) fits the cosmic energy density spectrum and is compatible within 2σ with the recent SNO result, showing the important interplay between any exotic energy loss mechanism and neutrino production. At lower energies, using also a ROSAT observation, only ∼ 3% of the X-ray intensity is explained. Data from orbiting X-ray Telescopes provide upper limits for particle decay rates 1 AU from the Sun, and suggest new types of searches on Earth or in space. In particular, X-ray observatories, with an unrivalled equivalent fiducial volume of ∼ 10 3 m 3 for the 0.1 -10 keV range, can search for the radiative decay of new particles even from existing data. This work introduces the elongation angle of the X-ray Telescope relative to the Sun as a relevant new parameter.

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The Physical Conditions in a Polar Coronal Hole and Nearby Regions from Norikura andSOHOObservations

Cited by 20 publications

References 37 publications

Solar coronal-hole plasma densities and temperatures

Solar coronal-hole plasma densities and temperatures

Solar Coronal Plumes

Observational evidence for gravitationally trapped massive axion(-like) particles

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