Cosmic-Ray Intensity Fluctuations at Sea Level

Abstract

Geomagnetic and atmospheric influences on sea-level cosmic radiation have been studied at Berkeley, California (95-m elevation, 44\ifmmode^\circ\else\textdegree\fi{} N geomagnetic latitude). The hard (20-cm lead absorber) and total intensities were measured with wide-angle triple-coincidence counter telescopes, and fluctuations of intensity were compared statistically with changes of barometric pressure, pressure-altitude, and temperature of the lower stratosphere. The atmospheric coefficients found by Duperier were verified for the 100-millibar region, but radiosonde data were not complete enough to permit calculations for higher strata of the atmosphere. The hard and total intensity data, corrected to constant barometric pressure, were examined for fluctuations that could be correlated with geomagnetic disturbances. No apparent cosmic-ray changes accompanied any of seven geomagnetic sudden commencements. Of eighteen magnetic storm periods occurring over eight months, only four appeared definitely to be accompanied by cosmic-ray intensity decreases. No increases of intensity occurred during these periods. Of the four decreases observed, two were unusual in that the decrease occurred an appreciable time before the measurable geomagnetic disturbance (May 27 and June 25, 1951). These two events occurred during times of very great sunspot activity, but only a loose genetic relationship could be established between the sunspot behavior and the prestorm cosmic-ray decreases.