VLF Phase Disturbances, HF Absorption, and Solar Protons in the PCA Events of 1967

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The ionization model developed in conjunction with VLF and HF propagation parameters from our analysis of the PCA's of August 28 and September 2, 1966, is applied in unmodified form to the 1967 events of January 28, February 2, May 23, and May 28. As for the 1966 events, proton intensities, energies, and cutoffs measured on the polar orbiting satellite 1963–38C are successfully connected to VLF phase disturbances and multifrequency riometer absorption increases. Considering all these events, the model provides the following rms fits between observed and computed values: 4.0 μ sec for 141 daytime and nighttime VLF phase values for seven paths at five frequencies during six proton events; 0.45 db for 181 riometer absorption values at 30 MHz during the six events; and 0.20 db for 36 riometer absorption values at 50 MHz during the two events that produced this absorption. The variability of the proton intensities and spectrums provides a rigorous test of the validity and internal consistency of the ionospheric model deduced through the complementary use of riometer absorption and VLF propagation changes occurring during PCA's. In the present analysis, as in the preceding one, the temporal variations in the proton cutoffs play an important role in the VLF analysis as a result of the lengths of the VLF transmission paths in relation to the polar‐cap area disturbed by the solar protons.