A geomagnetic cutoff rigidity interpolation tool: Accuracy verification and application to space weather

Abstract

We have developed a fast and accurate geomagnetic vertical cutoff rigidity interpolation tool that has general space weather applications. The interpolation tool utilizes vertical cutoff rigidity values determined from 5° by 5° world grids of geomagnetic cutoff rigidities obtained by tracing cosmic ray trajectories through the Tsyganenko magnetospheric field model combined with the International Geomagnetic Reference Field. The world grids for each UT hour were calculated for a 450-km satellite altitude for all magnetic conditions parameterized by the integer magnetic Kp index ranging from very quiet to extremely disturbed. The interpolation tool extrapolates from the grid positions at 450 km to any other position or altitude. We demonstrate the accuracy of vertical geomagnetic cutoff values obtained from this interpolation tool by reproducing the orbital radiation dose profile from solar protons recorded during the STS-28 space shuttle mission. We also predict the cutoff latitudes of the 8–15 MeV per nucleon α particle flux and compare these values with those determined by the SAMPEX (Solar Anomalous and Magnetospheric Particle Explorer) spacecraft observations for six independent solar particle events under a variety of geomagnetic conditions. In general our predicted cutoff latitudes are within about one degree of the observed cutoff latitudes for low levels of geomagnetic activity.