1,194 research outputs found
Relation between trees of fragmenting granules and supergranulation evolution
Context: The determination of the underlying mechanisms of the magnetic
elements diffusion over the solar surface is still a challenge. Understanding
the formation and evolution of the solar network (NE) is a challenge, because
it provides a magnetic flux over the solar surface comparable to the flux of
active regions at solar maximum. Aims: We investigate the structure and
evolution of interior cells of solar supergranulation. From Hinode
observations, we explore the motions on solar surface at high spatial and
temporal resolution. We derive the main organization of the flows inside
supergranules and their effect on the magnetic elements. Method: To probe the
superganule interior cell, we used the Trees of Fragmenting Granules (TFG)
evolution and their relations to horizontal Results: Evolution of TFG and their
mutual interactions result in cumulative effects able to build horizontal
coherent flows with longer lifetime than granulation (1 to 2 hours) over a
scale up to 12\arcsec. These flows clearly act on the diffusion of the
intranetwork (IN) magnetic elements and also on the location and shape of the
network. Conclusions: From our analysis during 24 hours, TFG appear as one of
the major elements of the supergranules which diffuse and advect the magnetic
field on the Sun's surface. The strongest supergranules contribute the most to
magnetic flux diffusion in the solar photosphere.Comment: 13 pages, 17 figures, accepted in Astronomy and Astrophysics movie :
http://www.lesia.obspm.fr/perso/jean-marie-malherbe/Hinode2007/hinode2007.htm
Can prominences form in current sheets
Two-dimensional numerical simulations of the formation of cold condensations in a vertical current sheet have been performed using the radiative, resistive MHD equations with line-tied boundary conditions at one end of the sheet. Prominence-like condensations are observed to appear above and below an X-line produced by the onset of the tearing-mode instability. Cooling in the sheet is initiated by Ohmic decay, with the densest condensations occurring in the region downstream of a fast-mode shock. This shock, which is due to the line-tied boundary conditions, terminates one of the two supermagnetosonic reconnection jets that develop when the tearing is fully developed. The condensation properties of shock waves, which may trigger or considerably enhance the conditions for thermal condensation are emphasized
On the thermal durability of solar prominences, or how to evaporate a prominence
The thermal disappearance of solar prominences under strong perturbations due to wave heating, Ohmic heating, viscous heating or conduction was investigated. Specifically, how large a thermal perturbation is needed to destroy a stable thermal equilibrium was calculated. It was found that the prominence plasma appears to be thermally very rugged. Its cold equilibrium may most likely be destroyed by either strong magnetic heating or conduction in a range of parameters which is relevant to flares
Radio Frequency Interference /RFI/ design guide for aerospace communications systems
Radio frequency interference design guide for aerospace communications system
DU Explorer et Comprendre l'Univers: introduction Ă la physique du Soleil
LicenceCe cours de niveau L1 donne les principales clefs pour comprendre les questions qui se posent en physique du Soleil
Controlling the composition of a confined fluid by an electric field
Starting from a generic model of a pore/bulk mixture equilibrium, we propose
a novel method for modulating the composition of the confined fluid without
having to modify the bulk state. To achieve this, two basic mechanisms -
sensitivity of the pore filling to the bulk thermodynamic state and electric
field effect - are combined. We show by Monte Carlo simulation that the
composition can be controlled both in a continuous and in a jumpwise way. Near
the bulk demixing instability, we demonstrate a field induced population
inversion in the pore. The conditions for the realization of this method should
be best met with colloids, but being based on robust and generic mechanisms, it
should also be applicable to some molecular fluids.Comment: 9 pages, 5 figure
Investigation of dynamic stresses in detona- tion technical note no. 7
Axial and hoop stress calculation in blast loaded thin walled cylindrical pressure vessel
The New 2018 Version of the Meudon Spectroheliograph
Daily full-disk observations of the solar photosphere and chromosphere
started at Meudon Observatory in 1908. After a review of the scientific context
and the historical background, we describe the instrumental characteristics and
capabilities of the new version operating since 2018. The major change is the
systematic recording of full line profiles over the entire solar disk providing
3D data cubes. Spectral and spatial sampling are both improved. Classical 2D
images of the Sun at fixed wavelength are still delivered. We summarize the
different processing levels of on-line data and briefly review the new
scientific perspectives.Comment: 14 pages, 5 figures; Published in Solar Physic
The photospheric solar oxygen project: II. Non-concordance of the oxygen abundance derived from two forbidden lines
In the Sun, the two forbidden [OI] lines at 630 and 636 nm were previously
found to provide discrepant oxygen abundances. aims: We investigate whether
this discrepancy is peculiar to the Sun or whether it is also observed in other
stars. method: We make use of high-resolution, high signal-to-noise ratio
spectra of four dwarf to turn-off stars, five giant stars, and one sub-giant
star observed with THEMIS, HARPS, and UVES to investigate the coherence of the
two lines. results: The two lines provide oxygen abundances that are
consistent, within observational errors, in all the giant stars examined by us.
On the other hand, for the two dwarf stars for which a measurement was
possible, for Procyon, and for the sub-giant star Capella, the 636 nm line
provides systematically higher oxygen abundances, as already seen for the Sun.
conclusions: The only two possible reasons for the discrepancy are a serious
error in the oscillator strength of the NiI line blending the 630 nm line or
the presence of an unknown blend in the 636 nm line, which makes the feature
stronger. The CN lines blending the 636 nm line cannot be responsible for the
discrepancy. The CaI autoionisation line, on the red wing of which the 636 nm
line is formed, is not well modelled by our synthetic spectra. However, a
better reproduction of this line would result in even higher abundances from
the 636 nm, thus increasing the discrepancy.Comment: A&A accepte
Constraints on filament models deduced from dynamical analysis
The conclusions deduced from simultaneous observations with the Ultra-Violet Spectrometer and Polarimeter (UVSP) on the Solar Maximum Mission satellite, and the Multichannel Subtractive Double Pass (MSPD) spectrographs at Meudon and Pic du Midi observatories are presented. The observations were obtained in 1980 and 1984. All instruments have almost the same field of view and provide intensity and velocity maps at two temperatures. The resolution is approx. 0.5 to 1.5" for H alpha line and 3" for C IV. The high resolution and simultaneity of the two types of observations allows a more accurate description of the flows in prominences as functions of temperature and position. The results put some contraints on the models and show that dynamical aspects must be taken into account
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