Abstract
As an extension of the trajectory calculations for asymptotic directions of cosmic-ray particles done by Hatton and Carswell (1963), the vertical threshold rigidities for 85 cosmic-ray stations have been determined with an accuracy of 0.1 GV. It is shown that the differences of the new threshold rigidities from those of Quenby and Wenk are not negligibly small for particular stations, and also that they are fairly sensitive to the difference of the geomagnetic field simulation adopted for the computation. The new rigidities are evaluated by applying them to typical cosmic-ray-disturbance events throughout the last solar cycle, namely a Forbush decrease in July, 1959, and two solar-flare particle increases in February, 1956, and November, 1960.
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