Solar corpuscular radiation and polar ionospheric disturbances

Study of disturbances in the polar inosphere yields considerable evidence of the existence of energetic solar particles associated with solar flares. Radio blackouts due to enhanced ionizations are classified into two characteristic types: the polar-cap blackout, and the auroral-zone blackout. It is shown that the polar-cap blackout appears with some hours' delay after a major solar radio out-burst of type IV, and is confined within the geomagnetic latitude of about 60° to 65°. The estimated energies of particles causing it are of about 10 to 100 Mev. The auroral-zone blackout then follows, accompanied by geomagnetic storms and auroras; it may be caused by the so-called auroral particles of 1 Mev or less. The energy spectrum of solar particles associated with solar flares is discussed in view of the present results and of information from various observations of solar and terrestrial disturbances. It is concluded that solar particles have a conspicuous suprathermal non-Maxwellian tail extending from a few kev up to relativistic energy ranges, though the main part of corpuscular clouds consists of particles of rather low energy, which therefore are likely to be in the Maxwellian distribution. The nature of solar corpuscular clouds and their effect upon the terrestrial ionosphere are also discussed.