1 / 12

Simulating Coronal Flux Tube Twisting by Photospheric Vortex Motions

This study simulates the twisting of a potential coronal flux tube by photospheric vortex motions. The flux tube evolves slowly, forming a helical shape, and shows potential eruption behavior above a critical twist. This model has the potential to lead to a better understanding of Coronal Mass Ejections (CMEs).

ecarey
Download Presentation

Simulating Coronal Flux Tube Twisting by Photospheric Vortex Motions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Abstract • We simulate the twisting of an initially potential coronal flux tube by photospheric vortex motions. • The flux tube starts to evolve slowly(quasi-statically) and possess helical shape. • There exists a critical twist, above which the flux tube would be observed as an eruption. • If the density is provided more realistically, this model is expected to lead to the structure of CMEs.

  2. 2. Numerical model2.1. Basic equations Compressible ideal MHD equations (β= 0) T: kinematic viscosity

  3. y 2.2. Initial configuration z two dipoles moment ±nz at (0, ±y0, -z0)

  4. 2.3. Imposed vortex motions A twisting velocity field is prescribed in the base plane and is chosen such that the velocity always point along the contours of Bz.

  5. 2.4. Numerical implementation simulation domain : [−100, 100]×[0, 100]×[0, 100] grid size : 195×165×150, nonuniform Cartesian grid time step : variable step according to the CFL criterion bottom boundary : u is given by imposed vortex motion Bx,y are obtained by extrapolation, ρ=ρ0 upper and lateral boundaries : ρ=ρ0, u = 0, and B = B0

  6. 3. Quasi-static and dynamic evolution …3.1. Flux tube expansion

  7. 3.2. Evolution of energy, current, Lorentz forces, and twist t = 54 (solid), t =75 (dotted), and t = 102 (dashed)

  8. 3.3. Influence of the central sheer Evolution of apex height and rise velocity of the central field line, and different dipole half distances. The evolution of the twisted flux tube is qualitatively similar for all cases. This shows that a sufficiently twisted tube erupt also in absence ob share.

  9. 3.4. Influence of the initial density distribution and the driving velocity Evolution of apex height and rise velocity of the central field line for different initial density profiles. The distribution of density should have no influence on the evolution in the quasi-static phase. It is, however, expected to have a strong influence on the expansion of the system in the dynamic phase

  10. 5. Sigmoidal shape The highest current density in our system does not occur on the central field line (left). The flux bundle from the highest current density has an inverse S shape (right), in agreement with the tendency of soft X-ray sigmoids that are rooted in α < 0 regions

  11. 6. Conclusion (1) A twisted magnetic flux tube start to evolve quasi-statically through a sequence of stable ideal-MHD equilibria to a good approximation. (2) There is a critical end-to-end twist, Φc. Above Φc the flux tube begin to erupt. (3) Essential properties remain unchanged if shear is created between the vortices. (4) 2.5π< Φc < 2.75π(for a particular set of parameters) (5) In a more realistic model, it is expected to form a configuration observed in CMEs.

More Related