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| Titel |
A Global 3D Bow Shock Model Valid for a Wide Range of Upstream Mach Numbers |
| VerfasserIn |
Jan Merka, David Sibeck, Yongli Wang |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250099195
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| Publikation (Nr.) |
 EGU/EGU2014-14978.pdf |
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| Zusammenfassung |
| Interaction of the supersonic solar wind with Earth’s magnetosphere creates fast mode
magnetosonic waves that travel back upstream, combine and steepen to form the bow
shock wave. The bow shock wave has been studied for more than four decades but
existing models are still often inaccurate. Previous studies established that bow shock
shape and position are primarily controlled by solar wind pressure, upstream Mach
numbers, interplanetary magnetic ?eld orientation and magnetopause shape and
position.
We have collected a total of 28,287 bow shock crossings identi?ed in observations from
the Cluster 1-4, Geotail, IMP-8, Interball-1, MAGION-4, THEMIS A-E and WIND
spacecraft and use this database to predict bow shock position as a function of solar wind
parameters. The large dataset appeared sufficient for employing a modelling technique that
does not assume a prescribed shock shape to eliminate a potential bias: The Support Vector
Regression Machine (SVRM) technique for mapping multi-dimensional data into a high-
dimensional feature space via nonlinear mapping through a selected kernel function and
performing a linear regression in this space. After a thorough study, we have concluded that
even though the employed number of shock crossings is the largest used by at least
an order of magnitude, the fitted data points are still unevenly distributed in the
modeled phase space and that severely limits the validity and applicability of the
SVRM-produced bow shock models. Therefore, the same database of bow shock
crossings is fitted using a method similar to Peredo et al. [1995] which presumes a
general 3D second-order bow shock shape parameterized by the upstream dynamic
pressure and Alfven Mach number values. The use of a prescribed shock shape
results in a model that provides accurate predictions for Alfven Mach numbers
as low as 2 and can be used with confidence up to 40 Re along the magnetotail. |
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