The February 5, 1965, solar proton event: 2. Low‐energy proton observations and their relation to the magnetosphere

Observations of the temporal and spatial behavior of low‐energy (∼‐Mev) solar protons are presented for the solar proton event of February 5, 1965, utilizing data fom the near‐earth satellites 1963 38C and Injun 4 and spaceprobe Mariner 4. An enhancement of low‐energy proton intensities is observed at invariant latitudes Λ ≳ 80° and may be a low‐latitude effect of the high‐latitude topology of the magnetopause. Comparison of the polar cap and Mariner 4 observations indicate that the magnetospheric configuration varies as the boundary conditions imposed by the interplanetary medium vary, thereby causing marked structure in the polar cap proton intensities. Further comparisons of the polar cap and Mariner 4 observations are presented and discussed in terms of (1) a filamentary interplanetary field structure and (2) an extended geomagnetic tail. Depending on the assumptions, either approach is consistent with the data. It is also indicated that particle motion across interplanetary field lines near the solar surface or in the region of the shock front is required to explain the low‐energy proton arrival times in the vicinity of the earth.