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  • 1
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    Modeling coronal evolution (1994)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Helmet streamers on the sun were observed to be the site of coronal mass ejections, dynamic events that eject coronal plasma and magnetic fields into the solar wind. A two dimensional (azimuthally symmetric) helmet streamer configuration was developed by computing solutions of the time dependent magnetohydrodynamic (MHD) equations, for a specified magnetic flux distribution on the sun. The helmet streamer is not symmetric about the equator. The evolution of the configuration, when differential rotation is applied, was investigated. It was found that after many rotations the configuration does not reach a steady state, but disrupts recurrently with the ejection of a plasmoid. These results suggest that differential rotation may be one of the mechanisms by which mass ejections are initiated.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 3rd SOHO Workshop on Solar Dynamic Phenomena and Solar Wind Consequences; p 249-252
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  • 2
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    Joint observations of the chromosphere, transition region, and corona from SOHO and NSO/Kitt Peak (1994)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The ground-based observing facilities of the National Solar Observatory (NSO) are reviewed from the perspective of joint observations with SOHO. A specific proposal is presented for observations of the HE-I 1083.0 nm line with the NASA/NSO spectromagnetograph and He 10830 video filtergraph/magnetograph in coordination with ultraviolet sensitive instruments on SOHO. The first task will be to look for associations of low-temperature transition-region lines with He 1083 nm absorption to investigate Andretta's conjecture, i.e. that the He 1083 nm line is formed in two layers where extreme ultraviolet radiation produced both in the low-temperature transition region (the upper layer) and in the surrounding corona products - a lower layer of absorption in the upper chromosphere.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 3rd SOHO Workshop on Solar Dynamic Phenomena and Solar Wind Consequences; p 345-354
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  • 3
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    Coronal fine structure as seen in the Skylab white light coronagraph (1994)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The white light coronograph (WLC) on Skylab provided an opportunity to study the corona at high spatial and temporal resolution. The spatial resolution of the instrument was approximately 25 cm with images taken approximately one per min. One set of images taken over a 10 min period was digitized, providing ten high spatial resolution images for analysis. The progress in data processing techniques available at the time was not sufficient to permit a reliable study of the fine structure in these images. Using current techniques an investigation of the sizes and lifetimes of the smallest scale features in the data was carried out. A preliminary analysis of an area between 2 and 3 Ro was completed. The results show that very narrow rays extend from at least 2 to 3 Ro. The narrowest of these rays has a thickness of approximately 75 cm. The contrast is so low that they are very close to the noise limit of the data. Most of the rays observed become unrecognizable after 10 min, although some remain visible over the entire time. Some notion seems to be detectable in the fine structure rays, but analysis of more frames will be needed to quantify these results.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 3rd SOHO Workshop on Solar Dynamic Phenomena and Solar Wind Consequences; p 227-230
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  • 4
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    X-ray absorbing structures in the Yohkoh images of the corona (1994)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Filaments, flare sprays, prominences and 'post-flare' loops are familiar to H alpha observers in their frequent appearances 'in absorption', dark against the chromospheric background or plages. Observations of the X-ray corona are generally interpreted as due to emission via optically thin thermal bremsstrahlung. Several cases of X-ray coronal structures in Yohkoh images, due to high opacity, absorbing matter in coronograph loops, are presented. The presence of the absorbing matter, mixed with emitting matter, complicates inference of physical parameters such as emission measures in X-ray sources. In the case of well defined features, absorption provides an opportunity to infer density. Quantitative estimates of the attenuation due to the absorption in example features are presented.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 3rd SOHO Workshop on Solar Dynamic Phenomena and Solar Wind Consequences; p 203-206
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  • 5
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    Acceleration of energetic particles which accompany coronal mass ejections (1994)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The causal association of major solar particle events seen at earth with coronal mass ejections (CME's), and not with solar flares, is discussed. Evidence that led to the demise of the flare dominated paradigm for major solar energetic particle events are described. The possibility of distinguishing particles from impulsive and gradual events using only observations is described. Particle acceleration at the CME level is discussed. Multi-spacecraft observations of CME events are described. Concerning the interplanetary CME, bidirectional proton events are discussed. Conclusions from progress in understanding the characteristics of solar energetic particles and their relation to the physical mechanisms of acceleration are given.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 3rd SOHO Workshop on Solar Dynamic Phenomena and Solar Wind Consequences; p 107-116
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  • 6
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    The deformation of flux tubes in the solar wind with applications to the structure of magnetic clouds and CMEs (1994)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Two dimensional magnetohydrodynamic simulations of the distortion of a magnetic flux tube, accelerated through ambient solar wind plasma, are presented. Vortices form on the trailing edge of the flux tube, and couple strongly to its interior. If the flux tube azimuthal field is weak, it deforms into an elongated banana-like shape after a few Alfven transit times. A significant azimuthal field component inhibits this distortion. In the case of magnetic clouds in the solar wind, it is suggested that the shape observed at 1 AU was determined by distortion of the cloud in the inner heliosphere. Distortion of the cloud beyond 1 AU takes many days. It is estimated that effective drag coefficients slightly greater than unity are appropriate for modeling flux tube propagation. Synthetic magnetic field profiles as would be seen by a spacecraft traversing the cloud are presented.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 3rd SOHO Workshop on Solar Dynamic Phenomena and Solar Wind Consequences; p 291-296
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  • 7
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    Near-Sun solar wind consequences of solar structure and dynamic phenomena observed by radio scintillation measurements (1994)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Since radio propagation measurements using either natural or spacecraft radio signals are used for probing the solar wind in the vicinity of the sun, they represent a key tool for studying the interplanetary consequences of solar structure and dynamic phenomena. New information on the near sun consequences was obtained from radio scintillation observations of coherent spacecraft signals. The results covering density fluctuations, fractional density fluctuations, coronal streamers, heliospheric current sheets, coronal mass ejections and interplanetary shocks are reviewed. A joint ICE S-band (13 cm wavelength) Doppler scintillation measurement with the SOHO white-light coronograph (LASCO) is described.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 3rd SOHO Workshop on Solar Dynamic Phenomena and Solar Wind Consequences; p 239-248
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  • 8
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    Features of the solar background velocity field (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The scaling properties of a time series of Doppler images obtained in good visibility conditions are studied. A 28 cm vacuum telescope and a vacuum spectroheliograph in video spectra-spectroheliograph mode, are used. Sixty line-of-sight Doppler images of an area of the quiet sun are investigated. They were taken at 60 sec intervals over a one hour span and have a 2 arcsec resolution. After the removal of the five-minute oscillations, the time-spatial spectrum is calculated. To study the turbulence of photospheric flows, two scaling parameters in the spectra, are estimated: the exponent of the spatial part of the power spectrum, and the exponent governing the scaling of time correlations. The implied diffusive behavior is discussed. This includes the estimation of a diffusion coefficient and the type of diffusion involved.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 2: Posters; p 249-252
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  • 9
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    Non-local transport in turbulent MHD convection (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The nonlocal non-diffusive transport of passive scalars in turbulent magnetohydrodynamic (MHD) convection is investigated using transilient matrices. These matrices describe the probability that a tracer particle beginning at one position in a flow will be advected to another position after some time. A method for the calculation of these matrices from simulation data which involves following the trajectories of passive tracer particles and calculating their transport statistics, is presented. The method is applied to study the transport in several simulations of turbulent, rotating, three dimensional compressible, penetrative MDH convection. Transport coefficients and other diagnostics are used to quantify the transport, which is found to resemble advection more closely than diffusion. Some of the results are found to have direct relevance to other physical problems, such as the light element depletion in sun-type stars. The large kurtosis found for downward moving particles at the base of the convection zone implies several extreme events.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 2: Posters; p 253-258
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  • 10
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    Tracking magnetogram proper motions by multiscale regularization (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Long uninterrupted sequences of solar magnetograms from the global oscillations network group (GONG) network and from the solar and heliospheric observatory (SOHO) satellite will provide the opportunity to study the proper motions of magnetic features. The possible use of multiscale regularization, a scale-recursive estimation technique which begins with a prior model of how state variables and their statistical properties propagate over scale. Short magnetogram sequences are analyzed with the multiscale regularization algorithm as applied to optical flow. This algorithm is found to be efficient, provides results for all the spatial scales spanned by the data and provides error estimates for the solutions. It is found that the algorithm is less sensitive to evolutionary changes than correlation tracking.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 2: Posters; p 227-232
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