Solar activity and polar cap absorption events

Abstract

The known facts about visible characteristics of solar flares and flare associated solar radio emission, solar ultraviolet and x-rays, solar cosmic rays and polar cap absorption, and solar corpuscular streams are briefly reviewed. Tables of data of the occurrence of these phenomena in conjunction with polar cap absorption (PCA) events are given. It is shown that all large PCA events, which are caused by solar cosmic rays, are associated with large solar flares. The cosmic rays created by flares on the eastern part of the sun’s disk are found to take up to 65 hours to reach the earth, while flares from the western part generally reach the earth in one or two hours. Type II and Type IV solar radio emissions apparently occur more frequently during the flares which create PCA than with all class 3 flares. Types I and III occur with almost every PCA event. All the flares which create PCA also cause strong sudden short wave fadeout, and often cause sudden cosmic noise absorption and sudden enhancement of atmospherics. It was found that the more intense the PCA event the shorter the time was between the flare and the onset of a sudden commencement magnetic storm. The more intense PCA also appeared to be associated with a more intense Forbush decrease. The theories of origin of the various types of solar emission are discussed, as are the theories of interplanetary magnetic fields and their plausibility from the standpoint of the observed PCA events.