Comparison between methods to compensate for the secular motion of the South Atlantic anomaly

Abstract

In order to avoid the prediction of artificially high particle fluxes, the static NASA trapped radiation models AP-8 and AE-8 should only be used with the same geomagnetic field models, for the same epochs, with which they were constructed. It is possible to correct for one aspect of the secular variation of the geomagnetic field, i.e. the secular drift of the local particle flux maximum in the South Atlantic Anomaly (SAA). The secular motion of the SAA may be compensated for by a coordinate transformation on the satellite trajectory corresponding to the inverse of the secular change of the geographic coordinates of the SAA. Three such transformations, defined by different approximations to the location of the centre of the SAA, are presented. The secular motion of the SAA is best represented by a longitudinal westward drift at a rate of 0.3°/year, in accordance with the findings of other authors. For a typical Shuttle orbit in the vicinity of the SAA, flux increases of a factor ten were found when the longitudinal correction is applied. In addition, the time of the encounter with the SAA may differ by as much as one orbital period from the time predicted without the correction.