Ordinary and Z-mode emissions from the Jovian polar region

The Ulysses Unified Radio and Plasma (URAP) experiment has detected a new component of Jupiter's radio spectrum in the frequency range from about 10 to 30 kHz. This component is emitted in the magnetoionic ordinary mode from a localized corotating source in the northern polar region. The source is centered at system III longitude 208°, near the meridian containing the North magnetic dipole axis, at a distance of nearly 4R_J from the planet and near the last closed field line. The emission frequency is somewhat above the electron plasma frequency in the source region, but well below the electron gyrofrequency. Accompanying this O-mode emission at lower frequencies is intense Z-mode emission, which is likely to play a significant role in the generation of the O-mode.