3 research outputs found
Numerical simulation of dark lanes in post-flare supra-arcade
We integrate the MHD ideal equations to simulate dark void sunwardly moving
structures in post--flare supra--arcades. We study the onset and evolution of
the internal plasma instability to compare with observations and to gain
insight into physical processes and characteristic parameters of these
phenomena. The numerical approach uses a finite-volume Harten-Yee TVD scheme to
integrate the 1D1/2 MHD equations specially designed to capture supersonic flow
discontinuities. The integration is performed in both directions, the sunward
radial one and the transverse to the magnetic field. For the first time, we
numerically reproduce observational dark voids described in Verwichte et al.
(2005). We show that the dark tracks are plasma vacuums generated by the
bouncing and interfering of shocks and expansion waves, upstream an initial
slow magnetoacoustic shock produced by a localized deposition of energy modeled
with a pressure perturbation. The same pressure perturbation produces a
transverse to the field or perpendicular magnetic shock giving rise to
nonlinear waves that compose the kink--like plasma void structures, with the
same functional sunward decreasing phase speed and constancy with height of the
period, as those determined by the observations.Comment: Accepted MNRAS, 6 pages, 7 figure
Numerical simulation of the internal plasma dynamics of post-flare loops
We integrate the MHD ideal equations of a slender flux tube to simulate the
internal plasma dynamics of coronal post-flare loops. We study the onset and
evolution of the internal plasma instability to compare with observations and
to gain insight into physical processes and characteristic parameters
associated with flaring events. The numerical approach uses a finite-volume
Harten-Yee TVD scheme to integrate the 1D1/2 MHD equations specially designed
to capture supersonic flow discontinuities. We could reproduce the
observational sliding down and upwardly propagating of brightening features
along magnetic threads of an event occurred on October 1st, 2001. We show that
high--speed downflow perturbations, usually interpreted as slow magnetoacoustic
waves, could be better interpreted as slow magnetoacoustic shock waves. This
result was obtained considering adiabaticity in the energy balance equation.
However, a time--dependent forcing from the basis is needed to reproduce the
reiteration of the event which resembles observational patterns -commonly known
as quasi--periodic pulsations (QPPs)- which are related with large scale
characteristic longitudes of coherence. This result reinforces the
interpretation that the QPPs are a response to the pulsational flaring
activity.Comment: Accepted MNRAS, 10 pages, 14 figures, 1 tabl