Observations of the fine structure of ion distribution function at the bow shock

The fast ion spectrometer SCA-1 on Interball Tail Probe measures 3-D ion distribution in the energy range 0.05–5.0 keV/Q in less than 10 sec. With new data we are testing the hypothesis, proposed on the basis of measurements on Prognoz-8 and Prognoz-10, that the thermalization of ion core on the strong Q-perpendicular shock front is provided by non-stationarity of the shock front. One supercritical Q-perpendicular bow shock crossing is analyzed. The downstream transmitted beam consists of multiple beams with thermal width of about upstream solar wind thermal width. This supports previous suggestion that the heated core of the downstream ion velocity distribution is formed of beamlets originating at patchy and oscillating structure of the shock front.