Changes in the High-Latitude East-West Asymmetry of Cosmic Rays

Abstract

A large long-term decrease in the east-west asymmetry has been observed at Hobart ($\ensuremath{\lambda}=52\ifmmode^\circ\else\textdegree\fi{}$S; near sea level). This is apparently related to the level of solar activity. In 1950 the asymmetry amounted to $\ensuremath{\alpha}=0.0246\ifmmode\pm\else\textpm\fi{}0.0022$, while in 1954 (a year of sunspot minimum) it was only 0.0108\ifmmode\pm\else\textpm\fi{}0.0016. It is shown that the decrease cannot be explained by changes in the parameters involved in the Johnson theory of the high-latitude east-west asymmetry, leading to the conclusion that the primary particles capable of producing a sea-level penetrating component at these latitudes are not completely isotropically distributed when they reach the upper atmosphere. The asymmetry is to be regarded as a very sensitive indicator of such anisotropy.