Universität zu Köln

Duling, Stefan, Saur, Joachim ORCID: 0000-0003-1413-1231 and Wicht, Johannes (2014). Consistent boundary conditions at nonconducting surfaces of planetary bodies: Applications in a new Ganymede MHD model. J. Geophys. Res-Space Phys., 119 (6). S. 4412 - 4441. WASHINGTON: AMER GEOPHYSICAL UNION. ISSN 2169-9402

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Abstract

The interaction of planetary bodies with their surrounding magnetized plasma can often be described with the magnetohydrodynamic (MHD) equations, which are commonly solved by numerical models. For these models it is necessary to define physically correct boundary conditions for the plasma mass and energy density, the plasma velocity, and the magnetic field. Many planetary bodies have surfaces whose electrical conductivity is negligibly small and thus no electric current penetrates their surfaces. Magnetic boundary conditions, which consider that the associated radial electric current at the planetary surface is zero, are difficult to implement because they include the curl of the magnetic field. Here we derive new boundary conditions by a decomposition of the magnetic field in poloidal and toroidal parts. We find that the toroidal part of the magnetic field needs to vanish at the surface of the insulator. For the spherical harmonics coefficients of the poloidal part, we derive a Cauchy boundary condition, which also matches a possible intrinsic field by including its Gauss coefficients. Thus, we can additionally include planetary dynamo fields as well as time-variable induction fields within electrically conductive subsurface layers. We implement the nonconducting boundary condition in the MHD simulation code ZEUS-MP using spherical geometry and provide a numerical implementation in Fortran 90 as supporting information on the JGR website. We apply it to a model for Ganymede's plasma environment. Our model also includes a consistent set of boundary conditions for the other MHD variables density, velocity, and energy. With this model we can describe Galileo spacecraft observations in and around Ganymede's minimagnetosphere very well.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Duling, Stefan UNSPECIFIED UNSPECIFIED UNSPECIFIED Saur, Joachim UNSPECIFIED orcid.org/0000-0003-1413-1231 UNSPECIFIED Wicht, Johannes UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-436352
DOI:	10.1002/2013JA019554
Journal or Publication Title:	J. Geophys. Res-Space Phys.
Volume:	119
Number:	6
Page Range:	S. 4412 - 4441
Date:	2014
Publisher:	AMER GEOPHYSICAL UNION
Place of Publication:	WASHINGTON
ISSN:	2169-9402
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language RADIATION MAGNETOHYDRODYNAMICS CODE; IRRADIANCE COMPARISON EXPERIMENT-1; 2 SPACE DIMENSIONS; MAGNETIC-FIELD; JOVIAN MAGNETOSPHERE; GALILEAN SATELLITES; ASTROPHYSICAL FLOWS; EUROPA; SIMULATIONS; CONSTRAINTS Multiple languages Astronomy & Astrophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/43635