Dynamic Fibrils Are Driven by Magnetoacoustic Shocks

Hansteen, V. H.; Pontieu, Bart De; Voort, L. Rouppe van der; Noort, M. van; Carlsson, Mats

doi:10.1086/507452

Cited by 286 publications

(403 citation statements)

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“…In the observations of Hansteen et al (2006) andDe Pontieu et al (2007) dynamic fibrils appear as dark "fingers" extending and retracting on top of a brighter background. They seem to be optically thick.…”

Section: Discussionmentioning

confidence: 99%

“…In this section we describe our implementation of Sollum's method in the MHD code developed in Oslo (Hansteen 2004). This code is based on the staggered grid code described in Dorch & Nordlund (1998), Mackay & Galsgaard (2001) and by Galsgaard & Nordlund 1 .…”

Section: Methodsmentioning

confidence: 99%

“…In addition, it treats radiative losses in strong lines and continua of hydrogen and Ca II in the upper chromosphere and transition region using an approximation based on detailed 1D computation with the RADYN code of Carlsson & Stein (1992). Thermal conduction along magnetic field lines is taken into account (Hansteen 2004).…”

Section: Methodsmentioning

confidence: 99%

“…We have performed a two-dimensional simulation including non-equilibrium hydrogen ionization in a setup similar to the one used by Hansteen et al (2006) andDe Pontieu et al (2007). It has a horizontal extent of 16.64 Mm with a resolution of 32.5 km and 512 cells in the horizontal direction.…”

Section: Simulation Setupmentioning

confidence: 99%

“…In this paper we first present our implementation of Sollum's method including back-coupling of the non-equilibrium ionization into the equation of state in the Oslo MHD code described by Hansteen (2004) which uses a finite difference scheme for the hydrodynamics. We then discuss an extensive 2D simulation of chromospheric fine-structure evolution with this code and analyze the results in terms of the hydrogen ionization balance, with separation between the chromospheric behavior above a magnetic element and in an area resembling quiet-sun internetwork.…”

Section: Introductionmentioning

confidence: 99%

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Non-equilibrium hydrogen ionization in 2D simulations of the solar atmosphere

Leenaarts

Carlsson

Hansteen

et al. 2007

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Context. The ionization of hydrogen in the solar chromosphere and transition region does not obey LTE or instantaneous statistical equilibrium because the timescale is long compared with important hydrodynamical timescales, especially of magneto-acoustic shocks. Since the pressure, temperature, and electron density depend sensitively on hydrogen ionization, numerical simulation of the solar atmosphere requires non-equilibrium treatment of all pertinent hydrogen transitions. The same holds for any diagnostic application employing hydrogen lines. Aims. To demonstrate the importance and to quantify the effects of non-equilibrium hydrogen ionization, both on the dynamical structure of the solar atmosphere and on hydrogen line formation, in particular Hα. Methods. We implement an algorithm to compute non-equilibrium hydrogen ionization and its coupling into the MHD equations within an existing radiation MHD code, and perform a two-dimensional simulation of the solar atmosphere from the convection zone to the corona. Results. Analysis of the simulation results and comparison to a companion simulation assuming LTE shows that: a) non-equilibrium computation delivers much smaller variations of the chromospheric hydrogen ionization than for LTE. The ionization is smaller within shocks but subsequently remains high in the cool intershock phases. As a result, the chromospheric temperature variations are much larger than for LTE because in non-equilibrium, hydrogen ionization is a less effective internal energy buffer. The actual shock temperatures are therefore higher and the intershock temperatures lower. b) The chromospheric populations of the hydrogen n = 2 level, which governs the opacity of Hα, are coupled to the ion populations. They are set by the high temperature in shocks and subsequently remain high in the cool intershock phases. c) The temperature structure and the hydrogen level populations differ much between the chromosphere above photospheric magnetic elements and above quiet internetwork. d) The hydrogen n = 2 population and column density are persistently high in dynamic fibrils, suggesting that these obtain their visibility from being optically thick in Hα also at low temperature.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%