Latitude-intensity structure and pitch-angle distributions of low-energy solar cosmic rays at low altitude

Solar protons (1.1–1.6 Mev) and alpha particles (4.1–15 Mev) were observed over the polar caps associated with the proton event of August 28, 1966. Persistent latitudinal structure in the proton flux was observed. Ordering of the structure by magnetic latitude over both polar caps during a given orbit shows that it is a spatial effect associated with nonuniform access of solar protons to high latitudes. Examples of the latitudinal structure are shown. Pitch-angle distributions were observed that clearly delineated a region of quasi-trapping; the changes in the pitch-angle distributions during a representative pass as the spacecraft 1966–70A traversed the region of quasi-trapping are shown. No evidence for the durable containment of the quasi-trapped solar alpha particles was observed.