Seasonal variations of cosmic-ray intensity in polar regions

Abstract

A seasonal variation of cosmic-ray intensity has been observed at two opposite polar stations, one at Thule in Greenland and the other at Wilkes in Antarctica. They are in antiphase, with a maximum in local winter. The seasonal variation can be accounted for almost completely by atmospheric effects, although a small extraterrestrial contribution cannot yet be excluded. We have found abnormally large values for the atmospheric temperature effects at these stations (a coefficient −8.3±0.9% km for the reference level of 300 mb at Thule and −12.5±2.1%/km at Wilkes). This can be ascribed to a low altitude of the effective muon-production level in polar regions.