A STUDY OF URANUS HOW SHOCK MOTIONS USING LANGMUIR-WAVES

During the Voyager 2 flyby of Uranus, strong electron plasma oscillati ons (Langmuir waves) were detected by the plasma wave instrument in th e 1.78-kHz channel on January 23-24, 1986, prior to the inbound bow sh ock crossing. Langmuir waves are excited by energetic electrons stream ing away from the bow shock. The goal of this work is to estimate the location and motion of Uranus' bow shock using Langmuir wave data, tog ether with the spacecraft positions and the measured interplanetary ma gnetic field. The following three remote sensing analyses were perform ed: the basic remote sensing method, the lag time method, and the trac e-back method. Because the interplanetary magnetic field was highly va riable, the first analysis encountered difficulties in obtaining a rea listic estimation of Uranus' bow shock motion. In the lag time method developed here, time lags due to the solar wind's finite convection sp eed are taken into account when calculating the shock's standoff dista nce. In the new trace-back method, limits on the standoff distance are obtained as a function of time by reconstructing electron paths. Most of the results produced by the latter two analyses are consistent wit h predictions based on the standard theoretical model and the measured solar wind plasma parameters. Differences between our calculations an d the theoretical model are discussed.