Timelines of cosmic ray intensity, Ap, IMF, and sunspot numbers since 1937

Abstract

An empirical approach is used to compute the equivalent annual mean hourly rates (%) for the Climax neutron monitor back to 1937, using the data of Forbush ion chamber at Cheltenham-Fredericksburg. They are compared with those given by McCracken and Beer (2007). We find their values to be systematically overestimated for 1937-1956 by a significant amount; also McCracken (2001) has understated the value of the mean rigidity of response to cosmic ray differential rigidity spectrum for polar 10Be data by as much as a factor of ∼2 too low. The annual mean values of the interplanetary magnetic field intensity (B) at Earth orbit are also computed to 1937, using Ap data, inferring that B has a floor at 3.3 nT. Comparing our pseudo-B values with those estimated by Svalgaard and Cliver (2007b), we find that their estimates are higher than ours in the late 1950s, 1940s, and 1930s. The pseudo neutron monitor rates are also used to compute the annual mean rates (%) for the low-energy ions at high altitudes and latitudes. They are compared with the sporadic balloon measurements made by Neher during 1933-1965. We infer that the higher flux measured by Neher in 1940 (of an unknown cause) for a few days did not persist long enough to show up in the annual mean ion chamber rate. © 2011 by the American Geophysical Union.