It is proposed that after a solar wind enhancement the wind‐magnetosphere interface becomes unstable with respect to production of ion acoustic waves. The high frequency electric oscillations then allow plasma to diffuse across the magnetic field, and the waves interact with the electron population via the cyclotron resonance. A small fraction of the electrons are accelerated to kev energies, and the energy distribution function is also distorted in the thermal region. Ultimately, the solar wind becomes locally subsonic with respect to the ion acoustic wave speed, and the waves travel upstream spreading the region of electron thermalization. Various stages in this relaxation process are described, and the theoretical predictions are compared with available experimental result