ELECTRON WHISTLER INTERACTION AT THE EARTHS BOW SHOCK .2. ELECTRON PITCH-ANGLE DIFFUSION

The effect of whistler waves on the electron distribution function is considered for the November 7, 1977, bow shock crossing. Order of magn itude estimates of the diffusion times due to whistler waves and to el ectrostatic noise shows that whistler waves are also effective in shap ing the electron distribution function f(e), causing pitch angle diffu sion in the limit of low frequencies. A Monte Carlo simulation of the electron dynamics, which includes electrostatic as well as whistler ra ndom terms, is then set up. A study of the diffusion coefficients, tog ether with the use of the experimental data on electromagnetic noise, allows us to assess spatial and velocity profiles for the random terms of the simulation. The moments of f(e), including the perpendicular t emperature and the heat flux densities, are reproduced satisfactorily by the numerical results. The resulting scenario for electron heating in quasi-perpendicular shocks can be described as follows: (1) the sho ck steady electric field in the deHoffman-Teller frame energizes the e lectrons, but the parallel temperature is too high and the perpendicul ar temperature too low, and a hole in f(e) is formed; (2) parallel dif fusion due to the electrostatic noise fills the hole in f(e) and creat es a flat-topped distribution, thus cooling the electrons, but the per pendicular temperature remains too low; (3) pitch angle diffusion due to whistler waves transfers energy from parallel to perpendicular, inc reasing the perpendicular temperature up to the observed values.