Extracting the February 1956 ground level enhancement event from legacy cosmic ray recordings

Abstract

Early continuous recordings of cosmic rays, as measured with Carnegie Type C Ionization Chambers, were made on rolls of photographic paper. This paper describes the extraction of the ionization data of the February 1956 ground level enhancement (GLE) event from the ionization chamber recordings of three stations, viz.: Godhavn, Cheltenham, and Christchurch. To verify the accuracy of the extraction algorithm a ground truth image of historic cosmic ray recordings was first constructed from the original image. A synthetic version of the ground truth image, which to some degree, reproduced the distortions and optical artefacts present in the original image was then created from the ground truth image. The detection algorithm was then applied to the synthetic image and the extracted values compared to the ground truth image to evaluate the detection capabilities of the algorithm, using measures such as MSE, precision, accuracy and recall The ionization data of the February 1956 GLE event was then extracted from the ionization chamber recordings and converted to percentage increase above background cosmic ray levels, for comparison to existing neutron monitor data which was sourced from a GLE database. The images share common attributes, and these include a sharp rise to a peak that tapers off more slowly. This trend is seen in all three data sets, and can be considered to be consistent with the neutron monitor data