Numerical MHD Simulation of the Coupled Evolution of Plasma and Magnetic Field in the Solar Chromosphere. I. Gradual and Impulsive Energisationстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 12 января 2016 г.
Аннотация:The dynamical coupling between solar chromospheric plasma and the magnetic
field is investigated by numerically solving a fully self-consistent, two-dimensional initialvalue
problem for the nonlinear collisional MHD equations including electric resistivity,
thermal conduction, and, in some cases, gas-dynamic viscosity. The processes in the contact
zone between two horizontal magnetic fields of opposite polarities are considered. The
plasma is assumed to be initially motionless and to have a temperature of 50,000 K uniform
throughout the plasma volume; the characteristic magnetic field corresponds to a plasma
β 1. In a physical time interval of 17 seconds typically covered by a computational run,
the plasma temperature gradually increases by a factor of two to three. Against this background,
an impulsive (in 0.1 seconds or less) increase in the current-aligned plasma velocity
occurs at the site of the current-layer thinning (sausage-type deformation, or m = 0 pinch
instability). This velocity burst can be interpreted physically as an event of suprathermalproton
generation. Further development of the sausage instability results in an increase in
the kinetic temperature of the protons to high values, even to those observed in flares. The
form of our system of MHD equations indicates that this kind of increase is a property of
the exact solution of the system for an appropriate choice of parameters. Magnetic reconnection
does not manifest itself in this solution: it would generate flows forbidden by the
chosen geometry. Therefore, the pinch-sausage effect can act as an energiser of the upper
chromosphere and be an alternative to the magnetic-reconnection process as the producer of
flares.