Access of solar protons to the Earth's polar caps

Energetic solar proton observations (Ep ≳ 300 kev) in the interplanetary medium by Explorer 33 and Explorer 35 and over the polar caps by Injun 5 during the period September 1968 through March 1970 have been examined in detail. The solar proton intensities observed over the polar regions were compared with the interplanetary intensities on an absolute basis. The high polar latitude (HPL) proton intensities tracked the magnetic field aligned interplanetary intensities well (solar-antisolar intensities as determined from the sectored Explorer data). The tracking was in agreement with the open magnetosphere model about 90% of the time. That is, the intensities observed on the HPL magnetic lines of force, which would be connected to magnetic lines of force from the sun in an interconnected geomagnetic and interplanetary magnetic field, were in agreement with the maximum intensity of the interplanetary proton pitch angle distribution. The intensities observed at the HPL region of the opposite polar cap were in agreement with the minimum intensity of the interplanetary pitch angle distribution. The low polar latitude (LPL) intensities generally tracked the maximum interplanetary intensity very well. The solar protons appear to have access to the LPL regions via the neutral sheet region of the magnetotail. Interplanetary proton intensity structures were used to estimate the delay in access to the polar caps. Based on the assumption that the interplanetary intensity structures are convected past the earth at solar wind speeds, the estimated delay times correspond to access regions with distances from the earth of about 100 RE for the north LPL region and 260 RE for the north HPL region. No evidence was found to indicate that the delays in access depend on the direction of the interplanetary magnetic field.