THE TERRESTRIAL BOW SHOCK IS THE BOUNDARY BETWEEN THE SUPERSONIC SOLAR WIND AND THE TERRESTRIAL MAGNETOSPHERE AND CONVERTS THE KINETIC ENERGY OF THE SOLAR WIND INTO THERMAL ENERGY ALLOWING THE FLOW TO BECOME SUBSONIC AND MOVE PAST THE MAGNETOSPHERE. SHOCKS ARE AN IMPORTANT ACCELERATION SITE FOR IONS AND ELECTRONS IN COLLISION LESS PLASMAS AND RESPONSIBLE FOR MUCH OF THE PARTICLE ACCELERATION IN SOLAR PLANETARY AND ASTROPHYSICAL REGIONS. ONE OF THE FUNDAMENTAL OUTSTANDING QUESTIONS OF ION ACCELERATION AT THE QUASI-PARALLEL BOW SHOCK IS WHICH PORTION OF SOLAR WIND IONS ARE ULTIMATELY SELECTED INTO THE SEED POPULATION THAT IS SUBSEQUENTLY ACCELERATED TO HIGH ENERGIES. IN ADDITION COMPOSITION MEASUREMENTS INDICATE THAT THE RATIO OF THE ENERGETIC TO SOLAR WIND HE++ FLUX IS ABOUT A FACTOR OF 2 LARGER THAN THE SAME FLUX RATIO FOR H+ WHEN THE TWO ION DISTRIBUTIONS ARE COMPARED AT EQUAL ENERGY PER CHARGE.

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