High-Altitude Cosmic-Ray Latitude Effect from 51° to 65°N Geomagnetic Latitude

Abstract

A significant latitude effect of approximately 45% for the total vertical cosmic-ray flux has been found over the region 51\ifmmode^\circ\else\textdegree\fi{}N to 65\ifmmode^\circ\else\textdegree\fi{}N at 10 g/${\mathrm{cm}}^{2}$ atmosphere depth in 1955. No evidence for a primary "knee" can be found separated from the air-path saturation effect with latitude. Since there is evidence that the $\ensuremath{\alpha}$ spectrum is flat north of 55\ifmmode^\circ\else\textdegree\fi{}, one concludes that the rigidity spectra of primary protons and $\ensuremath{\alpha}'\mathrm{s}$ differ over the corresponding rigidity region. Comparison of these data with telescope measurements of Pomerantz and McClure in 1950 does not show the anticorrelation with sunspot numbers found by Neher for ionchamber measurements. The data are not in disagreement with latitude coordinates 4\ifmmode^\circ\else\textdegree\fi{} higher suggested by studies of $\ensuremath{\alpha}$ particles, and, in fact, the observed latitude "saturation" effects are in better agreement with these new coordinates. A greatly increased counting rate was observed both at Minneapolis and Flin Flon, Manitoba, on August 26, 1955 at high altitude.