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| Titel |
Non-spherical source-surface model of the heliosphere: a scalar formulation |
| VerfasserIn |
M. Schulz |
| 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 ; 15, no. 11 ; Nr. 15, no. 11, S.1379-1387 |
| Datensatznummer |
250013001
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| Publikation (Nr.) |
 copernicus.org/angeo-15-1379-1997.pdf |
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| Zusammenfassung |
| The source-surface method offers an
alternative to full MHD simulation of the heliosphere. It entails specification
of a surface from which the solar wind flows normally outward along straight
lines. Compatibility with MHD results requires this (source) surface to be
non-spherical in general and prolate (aligned with the solar dipole axis) in
prototypical axisymmetric cases. Mid-latitude features on the source surface
thus map to significantly lower latitudes in the heliosphere. The model is
usually implemented by deriving the B field (in the region surrounded by
the source surface) from a scalar potential formally expanded in spherical
harmonics, with coefficients chosen so as to minimize the mean-square tangential
component of B over this surface. In the simplified (scalar) version the
quantity minimized is instead the variance of the scalar potential over the
source surface. The scalar formulation greatly reduces the time required to
compute required matrix elements, while imposing essentially the same physical
boundary condition as the vector formulation (viz., that the coronal magnetic
field be, as nearly as possible, normal to the source surface for continuity
with the heliosphere). The source surface proposed for actual application is a
surface of constant F̃ ≡ r-kB̃,
where r is the heliocentric distance and B̃ is the scalar
magnitude of the B field produced by currents inside the Sun. Comparison
with MHD simulations suggests that k ≈ 1.4 is a good choice for the
adjustable exponent. This value has been shown to map the neutral line on the
source surface during Carrington Rotation 1869 (May–June 1993) to a range of
latitudes that would have just grazed the position of Ulysses during that month
in which sector structure disappeared from Ulysses' magnetometer observations. |
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