Entity

Time filter

Source Type


Zhang Y.Z.,CAS Center for Space Science and Applied Research
Astrophysical Journal | Year: 2015

Using a 2.5-dimensional MHD simulation, we investigate the role played by the inner coronal null point in the formation and evolution of solar quiescent prominences. The flux rope is characterized by its magnetic fluxes, the toroidal magnetic flux Φ p and the poloidal flux Φφ. It is found that for a given Φ p , the catastrophe does not occur in the flux rope system until Φφ increases to a critical point. Moreover, the magnetic flux of the null point is the maximum value of the magnetic flux in the quadrupole background magnetic field, and represented by ψ N . The results show that the bigger ψ N usually corresponds to the smaller catastrophic point, the lower magnetic energy of the flux rope system, and the lesser magnetic energy inside the flux rope. Our results confirm that catastrophic disruption of the prominence occurs more easily when there is a bigger ψ N . However, ψ N has little influence on the maximum speed of the coronal mass ejections (CMEs) with an erupted prominence. Thus we argue that a topological configuration with the inner coronal null point is a necessary structure for the formation and evolution of solar quiescent prominences. In conclusion, it is easier for the prominences to form and to erupt as a core part of the CMEs in the magnetic structure with a greater ψ N . © 2015. The American Astronomical Society. All rights reserved.. Source


Zhang Y.Z.,CAS Center for Space Science and Applied Research
Astrophysical Journal | Year: 2013

Following the two-stage catastrophic flux rope model presented by Zhang et al., we investigate how magnetic flux emergence affects the formation and evolution of solar quiescent prominences. The magnetic properties of the flux rope are described with its toroidal magnetic flux per radian Φp and poloidal flux Φφ, and Φp is defined as the emerging strength (ES) of the magnetic flux. After the first catastrophe, the quiescent prominences are supported by the vertical current sheet and located in cavities below the curved transverse current sheet in the inner corona, for which both ES and Φφ are in the certain ranges. We calculate the strength range as 0.25 < ES < 0.50 for the quadrupolar field, and obtain the equation Φp Φφ = const., that is, the relationship between Φp and Φφ of the emerging flux for which the quiescent prominences are formed in the inner corona. After the second catastrophe, the quiescent prominences would either fall down onto the solar surface or erupt as an important part of coronal mass ejections. During the eruption of the quiescent prominences, most of the magnetic energy in the flux rope is lost, and less than half of the energy loss of the rope is released in the form of Alfvèn waves. We argue that there would be two important conditions required for the formation and eruption of solar quiescent prominences, a complicated source region and emerging toroidal magnetic flux that exceeds a critical strength. © 2013. The American Astronomical Society. All rights reserved. Source


Li G.,University of Alabama in Huntsville | Miao B.,Anhui University of Science and Technology | Hu Q.,University of Alabama in Huntsville | Qin G.,CAS Center for Space Science and Applied Research
Physical Review Letters | Year: 2011

The MHD turbulence theory developed by Iroshnikov and Kraichnan predicts a k-1.5 power spectrum. Solar wind observations, however, often show a k-5/3 Kolmogorov scaling. Based on 3 years worth of Ulysses magnetic field data where over 28000 current sheets are identified, we propose that the current sheet is the cause of the Kolmogorov scaling. We show that for 5 longest current-sheet-free periods the magnetic field power spectra are all described by the Iroshnikov-Kraichnan scaling. In comparison, for 5 periods that have the most number of current sheets, the power spectra all exhibit Kolmogorov scaling. The implication of our results is discussed. © 2011 American Physical Society. Source


Wang Y.,CAS Center for Space Science and Applied Research | Qin G.,CAS Center for Space Science and Applied Research
Astrophysical Journal | Year: 2015

This paper investigates the onset time of solar energetic particle (SEP) events with numerical simulations and analyzes the accuracy of the velocity dispersion analysis (VDA) method. Using a three-dimensional focused transport model, we calculate the fluxes of protons observed in the ecliptic at 1 AU in the energy range between 10 MeV and 80 MeV. In particular, three models are used to describe different SEP sources produced by flare or coronal shock, and the effects of particle perpendicular diffusion in the interplanetary space are also studied. We have the following findings. When the observer is disconnected from the source, the effects of perpendicular diffusion in the interplanetary space and particles propagating in the solar atmosphere have a significant influence on the VDA results. As a result, although the VDA method is valid with impulsive source duration, low background, and weak scattering in the interplanetary space or fast diffusion in the solar atmosphere, the method is not valid with gradual source duration, high background, or strong scattering. © 2015. The American Astronomical Society. All rights reserved.. Source


Wang Y.,CAS Center for Space Science and Applied Research | Qin G.,CAS Center for Space Science and Applied Research
Astrophysical Journal | Year: 2015

The spatial and temporal invariance in the spectra of energetic particles in gradual solar events is reproduced in simulations. Based on a numerical solution of the focused transport equation, we obtain the intensity time profiles of solar energetic particles (SEPs) accelerated by an interplanetary shock in three-dimensional interplanetary space. The shock is treated as a moving source of energetic particles with a distribution function. The time profiles of particle fluxes with different energies are calculated in the ecliptic at 1 AU. According to our model, we find that shock acceleration strength, parallel diffusion, and adiabatic cooling are the main factors in forming the spatial invariance in SEP spectra, and perpendicular diffusion is a secondary factor. In addition, the temporal invariance in SEP spectra is mainly due to the effects of adiabatic cooling. Furthermore, a spectra invariant region, which agrees with observations but is different from the one suggested by Reames et al. is proposed based on our simulations. © 2015. The American Astronomical Society. All rights reserved. Source

Discover hidden collaborations