LONGITUDINAL DISTRIBUTION OF ANOMALOUS HYDROGEN NEAR THE SOLAR-WIND TERMINATION SHOCK

Gasdynamic calculations show that the solar wind termination shock has a prolate shape. Consequently, the angle between the shock normal vector and the magnetic field lines varies with the variation of longitude. Near the ecliptic, the minimum speed for an upstream ion to be reflected by the shock, or for a downstream ion to overtake the shock, decreases on the shock flanks. If these reflected ions constitute a seed population for a first-order Fermi acceleration, then the injection process will be most efficient on the flanks of the termination shock. We show that the injection efficiency falls off steeply near the nose part of the termination shock in the case of pickup hydrogen. The positive longitudinal gradients of anomalous hydrogen along the termination shock close to the ecliptic are calculated within the framework of a simple analytical model. We expect that these positive gradients can be detected by the Pioneer 11 and Voyager 1/2 spacecraft when they are near the termination shock.