267 research outputs found
Evolution of the Kippenhahn-Schlueter Prominence Model Magnetic Field Under Cowling Resistivity
We present the results from 1.5D diffusion simulations of the
Kippenhahn-Schlueter prominence model magnetic field evolution under the
influence of the ambipolar terms of Cowling resistivity. We show that initially
the evolution is determined by the ratio of the horizontal and vertical
magnetic fields, which gives current sheet thinning (thickening) when this
ratio is large (small) and a marginal case where a new characteristic current
sheet length scale is formed. After a timespan greater than the Cowling
resistivity time, the current sheet thickens as a power law of independent
of the ratio of the field strengths. These results imply that when Cowling
resistivity is included in the model, the tearing instability time scale is
reduced by more than one order of magnitude when the ratio of the horizontal
field to the vertical field is 20\% or less. These results imply that, over the
course of its lifetime, the structure of the prominence can be significantly
altered by Cowling resistivity, and in some cases will allow the tearing
instability to occur.Comment: 9 pages, 6 figures, accepted for publication in PAS
Prominence Activation by Coronal Fast Mode Shock
An X5.4 class flare occurred in active region (AR) NOAA11429 on 2012 March 7.
The flare was associated with very fast coronal mass ejection (CME) with its
velocity of over 2500 km/s. In the images taken with STEREO-B/COR1, a dome-like
disturbance was seen to detach from expanding CME bubble and propagated
further. A Type-II radio burst was also observed at the same time. On the other
hand, in EUV images obtained by SDO/AIA, expanding dome-like structure and its
foot print propagating to the north were observed. The foot print propagated
with its average speed of about 670 km/s and hit a prominence located at the
north pole and activated it. While the activation, the prominence was strongly
brightened. On the basis of some observational evidence, we concluded that the
foot print in AIA images and the ones in COR1 images are the same, that is MHD
fast mode shock front. With the help of a linear theory, the fast mode mach
number of the coronal shock is estimated to be between 1.11 and 1.29 using the
initial velocity of the activated prominence. Also, the plasma compression
ratio of the shock is enhanced to be between 1.18 and 2.11 in the prominence
material, which we consider to be the reason of the strong brightening of the
activated prominence. The applicability of linear theory to the shock problem
is tested with nonlinear MHD simulation
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