ELECTROMAGNETIC-WAVES WITH FREQUENCIES NEAR THE LOCAL PROTON GYROFREQUENCY - ISEE-3 1 AU OBSERVATIONS

Low Frequency (LF) electromagnetic waves with periods near the local p roton gyrofrequency have been detected in interplanetary space by the magnetometer onboard ISEE-3. Transverse peak-to-peak amplitudes as lar ge as DELTAB/\B\ approximately 0.4 have been noted with compressional components (DELTA\B\/\B\) typically less-than-or-equal-to 0.1. General ly, the waves have even smaller amplitudes, or are not detectable with in the solar wind turbulence. The waves are elliptically/linearly pola rized and are often, but not always, found to propagate nearly along B (o). Both right- and left-hand polarizations in the spacecraft-frame h ave been detected. The waves are observed during all orientations of t he interplanetary magnetic field, with the Parker spiral orientation b eing the most common case. Because the waves are detected at and near the local proton cyclotron frequency, the generation mechanism must al most certainly be solar wind pickup of freshly created hydrogen ions. Possible sources for the hydrogen are the Earth's atmosphere, coronal mass ejections from the Sun, comets and interstellar neutral atoms. At this time it is not obvious which potential source is the correct one . Statistical tests employing over one year of ISEE-3 data will be don e in the near future to eliminate/confirm some of these possibilities.