Brief Description:
Prediction of magnetic rigidity (momentum/charge) cutoffs or thresholds
for penetration of energetic cosmic ray particles from interplanetary
space through Earth's geomagnetic field to the lower atmosphere was
pioneered by Carl Stoermer in 1930 as the true nature of these particles
was just becoming known. In the 1950's and thereafter the development of
increasingly fast computers allowed detailed predictions of charged
particle trajectories through complex multipolar models of the
geomagnetic field. From the 1970's to the present the standard software
for such computations has been that of Margaret (Peggy) A. Shea and Don
F. Smart, both originally at the old Air Force Geophysics Laboratory in
Massachusetts and now affiliated with the University of Alabama at
Huntsville. Updated FORTRAN 77 versions of this software, test files for
input and output, and accompanying documentation in Microsoft Word format,
have recently been archived at the National Space Science Data Center
through funding support from NASA Grant NAG5-8009. This software
determines allowed trajectories reaching specified locations near or
above the Earth's surface for a given range of magnetic rigidities and
incidence directions. The lower limit of the rigidity range for allowed
trajectories approximately defines the local cosmic ray cutoff. Cutoff
averaging is needed at some locations and directions for penumbral
effects of partial shadowing by the body of the Earth. Choices of models
for the geomagnetic field include IGRF-95 and other older models in the
NASA ALLMAG subroutines.
Availability: The Fortran code is available from the NSSDC/SPDF archive at ftp://nssdcftp.gsfc.nasa.gov/models/cosmic_rays/cutoff_rigidity_sw/.
References:
Included in software documentation.
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