MAGNETO-ACOUSTIC WAVES IN SUNSPOTS: FIRST RESULTS FROM A NEW THREE-DIMENSIONAL NONLINEAR MAGNETOHYDRODYNAMIC CODE

Journal Article · Tue Aug 10 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/719/1/357· OSTI ID:21455008

Felipe, T; Khomenko, E; Collados, M ^[1]

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1. Instituto de Astrofisica de Canarias, 38205, C/ Via Lactea, s/n, La Laguna, Tenerife (Spain)

Waves observed in the photosphere and chromosphere of sunspots show complex dynamics and spatial patterns. The interpretation of high-resolution sunspot wave observations requires modeling of three-dimensional (3D) nonlinear wave propagation and mode transformation in the sunspot upper layers in realistic spot model atmospheres. Here, we present the first results of such modeling. We have developed a 3D nonlinear numerical code specially designed to calculate the response of magnetic structures in equilibrium to an arbitrary perturbation. The code solves the 3D nonlinear MHD equations for perturbations; it is stabilized by hyper-diffusivity terms and is fully parallelized. The robustness of the code is demonstrated by a number of standard tests. We analyze several simulations of a sunspot perturbed by pulses of different periods at a subphotospheric level, from short periods, introduced for academic purposes, to longer and realistic periods of 3 and 5 minutes. We present a detailed description of the 3D mode transformation in a non-trivial sunspot-like magnetic field configuration, including the conversion between fast and slow magneto-acoustic waves and the Alfven wave, by calculation of the wave energy fluxes. Our main findings are as follows: (1) the conversion from acoustic to the Alfven mode is only observed if the driving pulse is located out of the sunspot axis, but this conversion is energetically inefficient; (2) as a consequence of the cutoff effects and refraction of the fast magneto-acoustic mode, the energy of the evanescent waves with periods around 5 minutes remains almost completely below the level {beta} = 1; (3) waves with frequencies above the cutoff propagate field aligned to the chromosphere and their power becomes dominating over that of evanescent 5 minute oscillations, in agreement with observations.

• OSTI ID: 21455008
• Journal Information: Astrophysical Journal, Vol. 719, Issue 1; Other Information: DOI: 10.1088/0004-637X/719/1/357; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ALFVEN WAVES
CHROMOSPHERE
MAGNETIC FIELD CONFIGURATIONS
MAGNETOHYDRODYNAMICS
NONLINEAR PROBLEMS
PERTURBATION THEORY
PHOTOSPHERE
SIMULATION
SUN
SUNSPOTS
THREE-DIMENSIONAL CALCULATIONS
WAVE PROPAGATION
ATMOSPHERES
FLUID MECHANICS
HYDRODYNAMICS
HYDROMAGNETIC WAVES
MAIN SEQUENCE STARS
MECHANICS
SOLAR ACTIVITY
SOLAR ATMOSPHERE
STARS
STARSPOTS
STELLAR ACTIVITY
STELLAR ATMOSPHERES