Evolution of magnetohydrodynamic waves in low layers of a coronal hole

Journal Article · Thu Nov 20 00:00:00 EST 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/796/1/43· OSTI ID:22370193

Pucci, Francesco; Malara, Francesco ^[1]; Onofri, Marco ^[2]

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1. Dipartimento di Fisica, Università della Calabria, Rende (CS), I-87036 (Italy)
2. Tri Alpha Energy, PO Box 7010, Rancho Santa Margarita, CA 92688 (United States)

Although a coronal hole is permeated by a magnetic field with a dominant polarity, magnetograms reveal a more complex magnetic structure in the lowest layers, where several regions of opposite polarity of typical size of the order of 10{sup 4} km are present. This can give rise to magnetic separatrices and neutral lines. MHD fluctuations generated at the base of the coronal hole by motions of the inner layer of the solar atmosphere may interact with such inhomogeneities, leading to the formation of small scales. This phenomenon is studied on a 2D model of a magnetic structure with an X-point, using 2D MHD numerical simulations. This model implements a method of characteristics for boundary conditions in the direction outer-pointing to Sun surface to simulate both wave injection and exit without reflection. Both Alfvénic and magnetosonic perturbations are considered, and they show very different phenomenology. In the former case, an anisotropic power-law spectrum forms with a dominance of perpendicular wavevectors at altitudes ∼10{sup 4} km. Density fluctuations are generated near the X-point by Alfvén wave magnetic pressure and propagate along open fieldlines at a speed comparable to the local Alfvén velocity. An analysis of energy dissipation and heating caused by the formation of small scales for the Alfvénic case is presented. In the magnetosonic case, small scales form only around the X-point, where a phenomenon of oscillating magnetic reconnection is observed to be induced by the periodic deformation of the magnetic structure due to incoming waves.

• OSTI ID: 22370193
• Journal Information: Astrophysical Journal, Vol. 796, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ALFVEN WAVES
ANISOTROPY
BOUNDARY CONDITIONS
DEFORMATION
DENSITY
DISTURBANCES
ENERGY LOSSES
FLUCTUATIONS
HYDROMAGNETIC WAVES
LAYERS
MAGNETIC FIELDS
MAGNETIC RECONNECTION
MAGNETOHYDRODYNAMICS
PERIODICITY
PERTURBATION THEORY
REFLECTION
SOLAR ATMOSPHERE
SPECTRA
STAR EVOLUTION
SUN