Atmospheric effects on cosmic-ray intensity near sea level

Abstract

Cosmic ray intensity variations of primary origin and those caused by meteorological changes appear superposed in records obtained from meson counter telescopes and neutron monitors at sea level. The study of either of these types of variation is thus greatly complicated by the presence of the other. In the present work, we have for the first time taken the step of processing the raw data to eliminate primary variations (and the inherent statistical fluctuations) so as to make possible a direct comparison of the remaining variations with the changes in atmospheric variables over the same period. The subsequent analysis confirms the expectation that there are no appreciable atmospheric effects on the intensity of the nucleonic component beyond the well-known effect associated with the sea level barometric pressure B. But in the meson case there is strong evidence that the widely used set of variables H₁₀₀, T₁₀₀ (the height and temperature of the 100-mb level) and B is not very suitable for representing atmospheric effects; it seems essential to include a variable representing temperatures in the lower part of the atmosphere, and the set of variables T₈₀₀ (temperature of the 800-mb layer), H₁₀₀, and B, with coefficients k_T = -.082 ± .008%/°C, k_H = -3.04 ± .61%/km, and k_B = -.134 ± .004%/mb appears to be the best. The theoretical formula of Dorman (1957), with a barometric coefficient β = -.147 ± .004%/mb and with the term representing the "temperature effect" reduced by a factor.76 ± .03, gives slightly better results. However, the improvement, at least in the case of the data we have analyzed, is too small to justify the great labor involved in using this formula.