ION DISTRIBUTION DYNAMICS NEAR THE EARTHS BOW SHOCK - FIRST MEASUREMENTS WITH THE 2D ION ENERGY SPECTROMETER CORALL ON THE INTERBALL TAIL-PROBE SATELLITE/

The dynamics of the ion distribution function near the Earth's bow sho ck is studied on the basis of quasi-3D measurements of ion energy spec tra in the range of 30-24200 eV/q with the Russian-Cuban CORALL instru ment on the INTERBALL/Tail-probe satellite. The instrument was designe d for observations of magnetospheric plasma and measures ions, in an a ngular range of 36 degrees-144 degrees from the Earth-Sun direction. I on populations generated by the Earth bow shock are often observed ups tream from the bow shock. In the solar-wind stream compressed and heat ed by the passing of very dense magnetic cloud (CME), two types of the se ion populations were measured upstream and before the bow shock cro ssing on 25 August 1995 at 07:37 UT. Both populations were observed in the energy range above 2 keV. At similar to 06:20 UT, when the angle between the direction of the interplanetary magnetic field and normal to the bow shock upsilon(Bn) was similar or equal to 43 degrees the in strument observed a narrow, fast (similar to 800 km/s) field-aligned b eam moving from the Earth. At similar to 07:30, when upsilon(Bn) simil ar or equal to 28 degrees, the wide ion pitch-angle distribution was o bserved. A similar suprathermal ion population is observed in the magn etosheath simultaneously with the solar-wind ion population being heat ed and deflected from the Sun-Earth direction. The similarity of obser vations during the mentioned time-interval and under usual solar-wind conditions allows us to conclude that types of suprathermal ion popula tions upstream and downstream from the bow shock do not depend on the solar-wind disturbance generated by magnetic cloud.