Increases of Ionization in the F2 Layer and Solar Corpuscular Radiation

Abstract

IN a recent communication, Orsini and Mazzilli¹ have directed attention to five further examples of sudden large increases of ionization in the F2, layer associated with major solar flares. Previous examples of such increases have been reported by Dieminger and Geisweid², Minnis and Bazzard³, Harrison⁴ and Knecht and Davies⁵. Table 1 shows when these events occurred, the geomagnetic threshold energies, E_c, for protons incident vertically at the stations where the increases in ionization were observed, and the associated, but generally delayed, increases in the intensity of energetic corpuscular radiation arriving in the vicinity of the Earth. These have been recorded by riometers, which are sensitive to particles such as protons arriving at the top of the atmosphere with energies of the order of 10 MeV. or more; by neutron monitors, which are affected by protons with energies greater than approximately 600 MeV.; and by ion chambers, which only record the arrival of primary protons having more than some 2 BeV.