The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
S Yashiro - One of the best experts on this subject based on the ideXlab platform.
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magnetic field strength in the upper Solar Corona using white light shock structures surrounding Coronal mass ejections
The Astrophysical Journal, 2012Co-Authors: Yong-jae Moon, Roksoon Kim, N Gopalswamy, K Cho, S YashiroAbstract:To measure the magnetic field strength in the Solar Corona, we examined 10 fast (1000 km s −1 ) limb Coronal mass ejections(CMEs) that show clear shock structures in Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph images. By applying the piston‐shock relationship to the observed CME’s standoff distance and electron density compression ratio, we estimated the Mach number, Alfv´ en speed, and magnetic field strength in the height range 3‐15 Solar radii (Rs). The main results from this study are as follows: (1) the standoff distance observed in the Solar Corona is consistent with those from a magnetohydrodynamic model and near-Earth observations; (2) the Mach number as a shock strength is in the range 1.49‐3.43 from the standoff distance ratio, but when we use the density compression ratio, the Mach number is in the range 1.47‐1.90, implying that the measured density compression ratio is likely to be underestimated owing to observational limits; (3) the Alfv´ en speed ranges from 259 to 982 km s −1 and the magnetic field strength is in the range 6‐105mG when the standoff distance is
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magnetic field strength in the upper Solar Corona using white light shock structures surrounding Coronal mass ejections
arXiv: Solar and Stellar Astrophysics, 2011Co-Authors: Yong-jae Moon, Roksoon Kim, N Gopalswamy, K Cho, S YashiroAbstract:To measure the magnetic field strength in the Solar Corona, we examined 10 fast (> 1000 km/s) limb CMEs which show clear shock structures in SOHO/LASCO images. By applying piston-shock relationship to the observed CME's standoff distance and electron density compression ratio, we estimated the Mach number, Alfven speed, and magnetic field strength in the height range 3 to 15 Solar radii (Rs). Main results from this study are: (1) the standoff distance observed in Solar Corona is consistent with those from a magnetohydrodynamic (MHD) model and near-Earth observations; (2) the Mach number as a shock strength is in the range 1.49 to 3.43 from the standoff distance ratio, but when we use the density compression ratio, the Mach number is in the range 1.47 to 1.90, implying that the measured density compression ratio is likely to be underestimated due to observational limits; (3) the Alfven speed ranges from 259 to 982 km/s and the magnetic field strength is in the range 6 to 105 mG when the standoff distance is used; (4) if we multiply the density compression ratio by a factor of 2, the Alfven speeds and the magnetic field strengths are consistent in both methods; (5) the magnetic field strengths derived from the shock parameters are similar to those of empirical models and previous estimates.
K Cho - One of the best experts on this subject based on the ideXlab platform.
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magnetic field strength in the upper Solar Corona using white light shock structures surrounding Coronal mass ejections
The Astrophysical Journal, 2012Co-Authors: Yong-jae Moon, Roksoon Kim, N Gopalswamy, K Cho, S YashiroAbstract:To measure the magnetic field strength in the Solar Corona, we examined 10 fast (1000 km s −1 ) limb Coronal mass ejections(CMEs) that show clear shock structures in Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph images. By applying the piston‐shock relationship to the observed CME’s standoff distance and electron density compression ratio, we estimated the Mach number, Alfv´ en speed, and magnetic field strength in the height range 3‐15 Solar radii (Rs). The main results from this study are as follows: (1) the standoff distance observed in the Solar Corona is consistent with those from a magnetohydrodynamic model and near-Earth observations; (2) the Mach number as a shock strength is in the range 1.49‐3.43 from the standoff distance ratio, but when we use the density compression ratio, the Mach number is in the range 1.47‐1.90, implying that the measured density compression ratio is likely to be underestimated owing to observational limits; (3) the Alfv´ en speed ranges from 259 to 982 km s −1 and the magnetic field strength is in the range 6‐105mG when the standoff distance is
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magnetic field strength in the upper Solar Corona using white light shock structures surrounding Coronal mass ejections
arXiv: Solar and Stellar Astrophysics, 2011Co-Authors: Yong-jae Moon, Roksoon Kim, N Gopalswamy, K Cho, S YashiroAbstract:To measure the magnetic field strength in the Solar Corona, we examined 10 fast (> 1000 km/s) limb CMEs which show clear shock structures in SOHO/LASCO images. By applying piston-shock relationship to the observed CME's standoff distance and electron density compression ratio, we estimated the Mach number, Alfven speed, and magnetic field strength in the height range 3 to 15 Solar radii (Rs). Main results from this study are: (1) the standoff distance observed in Solar Corona is consistent with those from a magnetohydrodynamic (MHD) model and near-Earth observations; (2) the Mach number as a shock strength is in the range 1.49 to 3.43 from the standoff distance ratio, but when we use the density compression ratio, the Mach number is in the range 1.47 to 1.90, implying that the measured density compression ratio is likely to be underestimated due to observational limits; (3) the Alfven speed ranges from 259 to 982 km/s and the magnetic field strength is in the range 6 to 105 mG when the standoff distance is used; (4) if we multiply the density compression ratio by a factor of 2, the Alfven speeds and the magnetic field strengths are consistent in both methods; (5) the magnetic field strengths derived from the shock parameters are similar to those of empirical models and previous estimates.
Roksoon Kim - One of the best experts on this subject based on the ideXlab platform.
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magnetic field strength in the upper Solar Corona using white light shock structures surrounding Coronal mass ejections
The Astrophysical Journal, 2012Co-Authors: Yong-jae Moon, Roksoon Kim, N Gopalswamy, K Cho, S YashiroAbstract:To measure the magnetic field strength in the Solar Corona, we examined 10 fast (1000 km s −1 ) limb Coronal mass ejections(CMEs) that show clear shock structures in Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph images. By applying the piston‐shock relationship to the observed CME’s standoff distance and electron density compression ratio, we estimated the Mach number, Alfv´ en speed, and magnetic field strength in the height range 3‐15 Solar radii (Rs). The main results from this study are as follows: (1) the standoff distance observed in the Solar Corona is consistent with those from a magnetohydrodynamic model and near-Earth observations; (2) the Mach number as a shock strength is in the range 1.49‐3.43 from the standoff distance ratio, but when we use the density compression ratio, the Mach number is in the range 1.47‐1.90, implying that the measured density compression ratio is likely to be underestimated owing to observational limits; (3) the Alfv´ en speed ranges from 259 to 982 km s −1 and the magnetic field strength is in the range 6‐105mG when the standoff distance is
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magnetic field strength in the upper Solar Corona using white light shock structures surrounding Coronal mass ejections
arXiv: Solar and Stellar Astrophysics, 2011Co-Authors: Yong-jae Moon, Roksoon Kim, N Gopalswamy, K Cho, S YashiroAbstract:To measure the magnetic field strength in the Solar Corona, we examined 10 fast (> 1000 km/s) limb CMEs which show clear shock structures in SOHO/LASCO images. By applying piston-shock relationship to the observed CME's standoff distance and electron density compression ratio, we estimated the Mach number, Alfven speed, and magnetic field strength in the height range 3 to 15 Solar radii (Rs). Main results from this study are: (1) the standoff distance observed in Solar Corona is consistent with those from a magnetohydrodynamic (MHD) model and near-Earth observations; (2) the Mach number as a shock strength is in the range 1.49 to 3.43 from the standoff distance ratio, but when we use the density compression ratio, the Mach number is in the range 1.47 to 1.90, implying that the measured density compression ratio is likely to be underestimated due to observational limits; (3) the Alfven speed ranges from 259 to 982 km/s and the magnetic field strength is in the range 6 to 105 mG when the standoff distance is used; (4) if we multiply the density compression ratio by a factor of 2, the Alfven speeds and the magnetic field strengths are consistent in both methods; (5) the magnetic field strengths derived from the shock parameters are similar to those of empirical models and previous estimates.
N Gopalswamy - One of the best experts on this subject based on the ideXlab platform.
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magnetic field strength in the upper Solar Corona using white light shock structures surrounding Coronal mass ejections
The Astrophysical Journal, 2012Co-Authors: Yong-jae Moon, Roksoon Kim, N Gopalswamy, K Cho, S YashiroAbstract:To measure the magnetic field strength in the Solar Corona, we examined 10 fast (1000 km s −1 ) limb Coronal mass ejections(CMEs) that show clear shock structures in Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph images. By applying the piston‐shock relationship to the observed CME’s standoff distance and electron density compression ratio, we estimated the Mach number, Alfv´ en speed, and magnetic field strength in the height range 3‐15 Solar radii (Rs). The main results from this study are as follows: (1) the standoff distance observed in the Solar Corona is consistent with those from a magnetohydrodynamic model and near-Earth observations; (2) the Mach number as a shock strength is in the range 1.49‐3.43 from the standoff distance ratio, but when we use the density compression ratio, the Mach number is in the range 1.47‐1.90, implying that the measured density compression ratio is likely to be underestimated owing to observational limits; (3) the Alfv´ en speed ranges from 259 to 982 km s −1 and the magnetic field strength is in the range 6‐105mG when the standoff distance is
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magnetic field strength in the upper Solar Corona using white light shock structures surrounding Coronal mass ejections
arXiv: Solar and Stellar Astrophysics, 2011Co-Authors: Yong-jae Moon, Roksoon Kim, N Gopalswamy, K Cho, S YashiroAbstract:To measure the magnetic field strength in the Solar Corona, we examined 10 fast (> 1000 km/s) limb CMEs which show clear shock structures in SOHO/LASCO images. By applying piston-shock relationship to the observed CME's standoff distance and electron density compression ratio, we estimated the Mach number, Alfven speed, and magnetic field strength in the height range 3 to 15 Solar radii (Rs). Main results from this study are: (1) the standoff distance observed in Solar Corona is consistent with those from a magnetohydrodynamic (MHD) model and near-Earth observations; (2) the Mach number as a shock strength is in the range 1.49 to 3.43 from the standoff distance ratio, but when we use the density compression ratio, the Mach number is in the range 1.47 to 1.90, implying that the measured density compression ratio is likely to be underestimated due to observational limits; (3) the Alfven speed ranges from 259 to 982 km/s and the magnetic field strength is in the range 6 to 105 mG when the standoff distance is used; (4) if we multiply the density compression ratio by a factor of 2, the Alfven speeds and the magnetic field strengths are consistent in both methods; (5) the magnetic field strengths derived from the shock parameters are similar to those of empirical models and previous estimates.
Eckart Marsch - One of the best experts on this subject based on the ideXlab platform.
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kinetic simulation of slow magnetosonic waves and quasi periodic upflows in the Solar Corona
The Astrophysical Journal, 2016Co-Authors: Wenzhi Ruan, Eckart Marsch, C. Vocks, Lei Zhang, Hardi Peter, Linghua WangAbstract:Quasi-periodic disturbances of emission-line parameters are frequently observed in the Corona. These disturbances propagate upward along the magnetic field with speeds of ~100 km s−1. This phenomenon has been interpreted as evidence of the propagation of slow magnetosonic waves or has been argued to be a signature of intermittent outflows superposed on the background plasmas. Here we aim to present a new "wave + flow" model to interpret these observations. In our scenario, the oscillatory motion is a slow-mode wave, and the flow is associated with a beam created by the wave–particle interaction owing to Landau resonance. With the help of a kinetic model, we simulate the propagation of slow-mode waves and the generation of beam flows. We find that weak periodic beam flows can be generated by to Landau resonance in the Solar Corona, and the phase with the strongest blueward asymmetry is ahead of that with the strongest blueshift by about 1/4 period. We also find that the slow wave damps to the level of 1/e after the transit time of two wave periods, owing to Landau damping and Coulomb collisions in our simulation. This damping timescale is similar to that resulting from thermal conduction in the MHD regime. The beam flow is weakened/attenuated with increasing wave period and decreasing wave amplitude since Coulomb collisions become more and more dominant over the wave action. We suggest that this "wave + flow" kinetic model provides an alternative explanation for the observed quasi-periodic propagating perturbations in various parameters in the Solar Corona.
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kinetic simulation of slow magnetosonic waves and quasi periodic upflows in the Solar Corona
arXiv: Solar and Stellar Astrophysics, 2016Co-Authors: Wenzhi Ruan, Eckart Marsch, C. Vocks, Lei Zhang, Hardi Peter, Linghua WangAbstract:Quasi-periodic disturbances of emission-line parameters are frequently observed in the Corona. These disturbances propagate upward along the magnetic field with speeds $\sim100~\rm{km~s}^{-1}$. This phenomenon has been interpreted as evidence of the propagation of slow magnetosonic waves or argued to be signature of the intermittent outflows superposed on the background plasmas. Here we aim to present a new "wave + flow" model to interpret these observations. In our scenario, the oscillatory motion is a slow mode wave, and the flow is associated with a beam created by the wave-particle interaction owing to Landau resonance. With the help of a Vlasov model, we simulate the propagation of the slow mode wave and the generation of the beam flow. We find that weak periodic beam flows can be generated owing to Landau resonance in the Solar Corona, and the phase with strongest blueward asymmetry is ahead of that with strongest blueshift by about 1/4 period. We also find that the slow wave damps to the level of 1/e after the transit time of two wave periods, owing to Landau damping and Coulomb collisions in our simulation. This damping time scale is similar to that resulting from thermal-conduction in the magnetohydrodynamics regime. The beam flow is weakened/attenuated with increasing wave period and decreasing wave amplitude since Coulomb collision becomes more and more dominant over the wave action. We suggest that this "wave + flow" kinetic model provides an alternative explanation for the observed quasi-periodic propagating perturbations in various parameters in the Solar Corona.
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Kinetic physics of the Solar Corona and Solar wind
Living Reviews in Solar Physics, 2006Co-Authors: Eckart MarschAbstract:Kinetic plasma physics of the Solar Corona and Solar wind are reviewed with emphasis on the theoretical understanding of the in situ measurements of Solar wind particles and waves, as well as on the remote-sensing observations of the Solar Corona made by means of ultraviolet spectroscopy and imaging. In order to explain Coronal and interplanetary heating, the microphysics of the dissipation of various forms of mechanical, electric and magnetic energy at small scales (e.g., contained in plasma waves, turbulences or non-uniform flows) must be addressed. We therefore scrutinise the basic assumptions underlying the classical transport theory and the related collisional heating rates, and also describe alternatives associated with wave-particle interactions. We elucidate the kinetic aspects of heating the Solar Corona and interplanetary plasma through Landau- and cyclotron-resonant damping of plasma waves, and analyse in detail wave absorption and micro instabilities. Importan! t aspects (virtues and limitations) of fluid models, either single- and multi-species or magnetohydrodynamic and multi-moment models, for Coronal heating and Solar wind acceleration are critically discussed. Also, kinetic model results which were recently obtained by numerically solving the Vlasov Boltzmann equation in a Coronal funnel and hole are presented. Promising areas and perspectives for future research are outlined finally.
