MAGNETOHYDRODYNAMIC PROCESSES IN THE INNER COMA OF COMET HALLEY

A two-fluid, two-dimensional, magnetohydrodynamical (MHD) model is use d to study the dynamics of the inner coma of comet Halley. Ion product ion, electron-ion recombination, charge transfer collisions, and ion-n eutral friction are included. The model adopts a cylindrical grid with nonuniform radial spacing extending from a cometocentric distance of 1000 km out to 10(7) km. A magnetic barrier and a diamagnetic cavity b oth appear in the model results, and the plasma flow is directed aroun d the cavity. Electron temperature profiles have recently been suggest ed for the inner coma in which large temperature enhancements (T-e app roximate to 25,000 K) are present at a radial distance of about 10,000 km and have been used to explain, via reduced recombination, the ion density enhancement observed by the Giotto ion and neutral mass spectr ometers at this location. Using our MHD model as well as analytical me thods we find that large electron temperature enhancements in the inne r coma result in large reductions in the magnetic field strength which were not observed by the Giotto magnetometer. We suggest that perhaps the electron temperature is only enhanced to a value of about 10,000 K rather than to 25,000 K at the ion pileup.