Electron pitch angle distributions throughout the magnetosphere as observed on Ogo 5

A survey of the equatorial pitch angle distributions of energetic electrons is provided for all local times out to radial distances of 20 RE on the night side of the earth and to the magnetopause on the day side of the earth. In much of the inner magnetosphere and in the outer magnetosphere on the day side of the earth, the normal loss cone distribution prevails. The effects of drift shell splitting (that is, the appearance of pitch angle distributions with minimums at 90°, called butterfly distributions) become apparent in the early afternoon magnetosphere at extended distances, and the distribution is observed in to 5.5 RE in the nighttime magnetosphere. Inside ∼9 RE the pitch angle effects are quite energy dependent. Beyond ∼9 RE in the premidnight magnetosphere during quiet times the butterfly distribution is often observed with j⊥/j∥ < 1/100. It is shown that these electrons cannot survive a drift to dawn without being considerably modified. The role of substorm activity in modifying these distributions is identified.