LOW-FREQUENCY ELECTROMAGNETIC PLASMA-WAVES AT COMET-P GRIGG-SKJELLERUP - OVERVIEW AND SPECTRAL CHARACTERISTICS

Large-amplitude electromagnetic plasma waves are one of the dominant f eatures of the solar wind-comet interaction. Wave characteristics stro ngly depend on parameters such as the solar wind flow and Alfven veloc ities and the angle between flow and interplanetary magnetic field as well as the production rate. With respect to the latter the flyby of t he spacecraft Giotto at comet P/Grigg-Skjellerup provides a unique pos sibility to study such waves in further detail. Pickup ion-related wav e signatures have been observed up to a distance of 600,000 km from th e nucleus. Peak spectral power in the spacecraft frame of reference oc curs at frequencies mainly somewhat below the water group ion gyrofreq uency. From this the waves are determined to be mainly left-hand polar ized waves, causing one-sided pitch angle diffusion outbound. The wave activity strongly increases close to the comet; upstream it exhibits a quadratic dependence on the water group pickup ion free energy. Furt hermore, a phenomenological study of the wave characteristics provides a unique description of the fine-structure of the interaction region. Indications of steepened magnetosonic waves have been found in the ou tbound magnetosheath region.