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| Titel |
LANL* V1.0: a radiation belt drift shell model suitable for real-time and reanalysis applications |
| VerfasserIn |
J. Koller, G. D. Reeves, R. H. W. Friedel |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 2, no. 2 ; Nr. 2, no. 2 (2009-07-29), S.113-122 |
| Datensatznummer |
250000540
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| Publikation (Nr.) |
 copernicus.org/gmd-2-113-2009.pdf |
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| Zusammenfassung |
| We describe here a new method for calculating the magnetic drift
invariant, L*, that is used for modeling radiation belt dynamics
and for other space weather applications. L* (pronounced L-star) is
directly proportional to the integral of the magnetic flux contained
within the surface defined by a charged particle moving in the Earth's
geomagnetic field. Under adiabatic changes to the geomagnetic field L*
is a conserved quantity, while under quasi-adiabatic fluctuations
diffusion (with respect to a particle's L*) is the primary term in
equations of particle dynamics. In particular the equations of motion
for the very energetic particles that populate the Earth's radiation
belts are most commonly expressed by diffusion in three dimensions:
L*, energy (or momentum), and pitch angle (the dot product of velocity
and the magnetic field vector). Expressing dynamics in these
coordinates reduces the dimensionality of the problem by referencing
the particle distribution functions to values at the magnetic
equatorial point of a magnetic "drift shell" (or L-shell) irrespective
of local time (or longitude). While the use of L* aids in simplifying
the equations of motion, practical applications such as space weather
forecasting using realistic geomagnetic fields require sophisticated
magnetic field models that, in turn, require computationally intensive
numerical integration. Typically a single L* calculation can require
on the order of 105 calls to a magnetic field model and each point in
the simulation domain and each calculated pitch angle has a different
value of L*. We describe here the development and validation of a
neural network surrogate model for calculating L* in sophisticated
geomagnetic field models with a high degree of fidelity at
computational speeds that are millions of times faster than direct
numerical field line mapping and integration. This new surrogate model
has applications to real-time radiation belt forecasting, analysis of
data sets involving tens of satellite-years of observations, and other
problems in space weather. |
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