Observations suggesting weak pitch angle diffusion of protons

A pronounced longitude variation in the intensity of locally mirroring protons above 100 kev in the L range 3.5–5 at low altitudes is observed. The observations can be accounted for by a steady-state pitch angle diffusion process. The pitch angle diffusion coefficient for protons mirroring near the loss cone at L = 4 is found to be about 10−6 sec−1.