MASS LOADING IN VELOCITY SHEARS

An analysis is presented on the motion of contaminant ions picked up b y the solar wind within velocity shears. An expression is obtained for the ion density in terms of the flow speed across the velocity shear. It is argued that enhanced densities occur in the region where the fl ow speed is small and that local values may become significantly large r than the ion density outside the velocity shear. A comparison is mad e with measurements obtained across the plasma wake of comet Giacobini -Zinner with the International Cometary Explorer (ICE) spacecraft. Wit hin the velocity shear of that comet's ionosheath the cometary ion den sity becomes large and reaches values that are different from those ex pected when the ion population depends only on the ionization of a uni form outflow of neutral particles from the cometary nucleus. The enhan ced plasma density expected within the velocity shear is compatible wi th the shape of the density profile of contaminant ions detected in th at region. (C) 1996 American Institute of Physics.