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| Titel |
Uncertainties in field-line tracing in the magnetosphere. Part I: the axisymmetric part of the internal geomagnetic field |
| VerfasserIn |
D. M. Willis, J. Robin Singh, J. Comer |
| 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. 2 ; Nr. 15, no. 2, S.165-180 |
| Datensatznummer |
250012625
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| Publikation (Nr.) |
 copernicus.org/angeo-15-165-1997.pdf |
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| Zusammenfassung |
| The technique of tracing along magnetic field
lines is widely used in magnetospheric physics to provide a "magnetic frame
of reference'' that facilitates both the planning of experiments and the
interpretation of observations. The precision of any such magnetic frame of
reference depends critically on the accurate representation of the various
sources of magnetic field in the magnetosphere. In order to consider this
important problem systematically, a study is initiated to estimate first the
uncertainties in magnetic-field-line tracing in the magnetosphere that arise
solely from the published (standard) errors in the specification of the
geomagnetic field of internal origin. Because of the complexity in computing
these uncertainties for the complete geomagnetic field of internal origin,
attention is focused in this preliminary paper on the uncertainties in
magnetic-field-line tracing that result from the standard errors in just the
axisymmetric part of the internal geomagnetic field. An exact analytic equation
exists for the magnetic field lines of an arbitrary linear combination of
axisymmetric multipoles. This equation is used to derive numerical estimates of
the uncertainties in magnetic-field-line tracing that are due to the published
standard errors in the axisymmetric spherical harmonic coefficients (i.e.
gn0 ± δgn0). Numerical results determined
from the analytic equation are compared with computational results based on
stepwise numerical integration along magnetic field lines. Excellent agreement
is obtained between the analytical and computational methods in the axisymmetric
case, which provides great confidence in the accuracy of the computer program
used for stepwise numerical integration along magnetic field lines. This
computer program is then used in the following paper to estimate the
uncertainties in magnetic-field-line tracing in the magnetosphere that arise
from the published standard errors in the full set of spherical harmonic
coefficients, which define the complete (non-axisymmetric) geomagnetic field of
internal origin. Numerical estimates of the uncertainties in magnetic-field-line
tracing in the magnetosphere, calculated here for the axisymmetric part of the
internal geomagnetic field, should be regarded as "first approximations''
in the sense that such estimates are only as accurate as the published standard
errors in the set of axisymmetric spherical harmonic coefficients. However, all
procedures developed in this preliminary paper can be applied to the derivation
of more realistic estimates of the uncertainties in magnetic-field-line tracing
in the magnetosphere, following further progress in the determination of more
accurate standard errors in the spherical harmonic coefficients. |
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