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Coordinates studies for mapping the radiation belt fluxes in low-altitude environment
 
The mapping of the low-altitude radiation belt environments in the classical (B, L) invariant coordinates is rather poorly resolved at low altitudes where the SAMPEX and DEMETER missions are collecting scientific data. This lack of adequate spatial resolution at low altitudes has been pointed out several times since 1986. A simple solution to this standing problem is is study at the CSR. It applies specially for mapping and modeling particle flux measurements collected from LEO missions.
Alternative coordinates were proposed in the 90s to improve the spatial resolution of binning meshes and radiation belt maps in the low-altitude region: i.e. near the atmospheric cut-off. We have defined a new coordinate system: the invariant altitude hinv (that we recommend instead of B or other invariant drift shell coordinates like B/B0 or Alpha0), and the equatorial pitch angle. In McIlwain's reference dipole the new drift shell coordinate, hinv, corresponds to the altitude (in units of km) of mirror points of particles which have given values of B and I or L, calculated by using a geomagnetic field model like the IGRF. The advantages and limitations of the new hinv coordinate have been studied. For comparison, the distributions of the omnidirectional fluxes of electrons and protons predicted by the standard AE8 and AP8 radiation belt models has been displayed using this new invariant coordinate, as well as by using alternative invariant coordinates like B/B0 or Alpha0.
A set of orbits of the SAMPEX, DEMETER and CRRES spacecraft has been displayed in these different coordinate systems, to illustrate the advantage of using the invariant altitude hinv to map the radiation belt environment at low altitudes.
 
See the article in Space Weather Journal.
Cabrera, J., and J. Lemaire (2007),
Using invariant altitude (hinv) for mapping of the radiation belt fluxes in the low-altitude environment,
Space Weather, 5, S04007, doi:10.1029/2006SW000263.
 
Download the code used in this article roberts.zip based on the Roberts algorithm

Contacts: Dr. Juan Cabrera
 
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