Long-term variations of geomagnetic rigidity cutoffs

Using trajectory calculations of cosmic rays in the geomagnetic field, the changes of vertical cutoff rigidities in the past are discussed. The computations are done for selected positions at the Earth's surface using the IGRF model data for 1900-2000. The contour maps of vertical cutoff rigidities using the set of ten Gauss coefficients for the period of years between 0 and 1600 are obtained. The trends in long-term variability of cutoffs at different positions on the Earth's surface are described.