  Seventy crossings of the Earths bow shock by the THEMIS satellites have been
used to study thermal electron heating in collisionless, quasi-perpendicular
shocks. It was found that the temperature increase of thermal electrons
differed from the magnetic field increase by factors as great as three, that
the parallel electron temperature increase was not produced by parallel
electric fields, and that the parallel and perpendicular electron temperature
increases were the same on the average. It was also found that the
perpendicular and parallel electron heating occurred simultaneously so that the
isotropization time is the same as the heating time. These results cannot be
explained by energy transfer from waves to electrons or by the motion of
magnetized electrons through the shock. Electric field fluctuations on the
scale of the electron gyro-diameter were found to be of finite amplitude in the
shock ramp, which requires that the electron trajectories be more random and
chaotic than orderly and adiabatic. The data may be explained by the large
amplitude electric field fluctuations that demagnetize electrons as they move
through the cross-shock electric field
