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| Titel |
A three-dimensional, iterative mapping procedure for the implementation of an ionosphere-magnetosphere anisotropic Ohm's law boundary condition in global magnetohydrodynamic simulations |
| VerfasserIn |
M. L. Goodman |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 13, no. 8 ; Nr. 13, no. 8, S.843-853 |
| Datensatznummer |
250011958
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| Publikation (Nr.) |
 copernicus.org/angeo-13-843-1995.pdf |
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| Zusammenfassung |
| The mathematical formulation of an iterative
procedure for the numerical implementation of an ionosphere-magnetosphere (IM)
anisotropic Ohm's law boundary condition is presented. The procedure may be used
in global magnetohydrodynamic (MHD) simulations of the magnetosphere. The basic
form of the boundary condition is well known, but a well-defined, simple,
explicit method for implementing it in an MHD code has not been presented
previously. The boundary condition relates the ionospheric electric field to the
magnetic field-aligned current density driven through the ionosphere by the
magnetospheric convection electric field, which is orthogonal to the magnetic
field B, and maps down into the ionosphere along equipotential
magnetic field lines. The source of this electric field is the flow of the solar
wind orthogonal to B. The electric field and current density in
the ionosphere are connected through an anisotropic conductivity tensor which
involves the Hall, Pedersen, and parallel conductivities. Only the
height-integrated Hall and Pedersen conductivities (conductances) appear in the
final form of the boundary condition, and are assumed to be known functions of
position on the spherical surface R=R1 representing the
boundary between the ionosphere and magnetosphere. The implementation presented
consists of an iterative mapping of the electrostatic potential ψ the
gradient of which gives the electric field, and the field-aligned current
density between the IM boundary at R=R1 and the inner
boundary of an MHD code which is taken to be at R2>R1.
Given the field-aligned current density on R=R2, as
computed by the MHD simulation, it is mapped down to R=R1
where it is used to compute ψ by solving the equation that is the IM
Ohm's law boundary condition. Then ψ is mapped out to R=R2,
where it is used to update the electric field and the component of velocity
perpendicular to B. The updated electric field and
perpendicular velocity serve as new boundary conditions for the MHD simulation
which is then used to compute a new field-aligned current density. This process
is iterated at each time step. The required Hall and Pedersen conductances may
be determined by any method of choice, and may be specified anew at each time
step. In this sense the coupling between the ionosphere and magnetosphere may be
taken into account in a self-consistent manner. |
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