Analysis of balloon observations during the April 1960, solar cosmic-ray events

Abstract

A series of balloon flights was conducted at Minneapolis, Minnesota, during the solar cosmic-ray events from April 1, 1960, through April 30, 1960. The largest event on April 1 was recorded by a balloon at high altitude, and for a power-law spectrum of the solar protons the exponent γ was determined to be 2.4. This spectrum, when extrapolated, agrees with the rates measured by the earth satellite Explorer 7 for the same event. It is shown that at Minneapolis a partial geomagnetic cutoff was in effect that limited the low-energy particles detected at balloon levels. Comparison of the simultaneous readings of the Pioneer 5 deep space probe confirms this picture. A relationship is established between the Deep River neutron monitor and various balloon instruments at high altitude, and the proportionality is determined during a large Forbush decrease. The event on April 28 was also detected at Minneapolis with balloons, and the data are consistent with time variations in the local geomagnetic cutoff. The paper includes many details of the construction of the ion chambers, counters, and telemetry system used for the balloon monitoring program at Minnesota.