Comparison of natural narrow-banded emissions and sounder stimulated resonances in the magnetosphere of Jupiter observed with the Ulysses spacecraft

Summary form only given. The sounder stimulated resonances observed by Ulysses in Jupiter´s lo torus revealed a spectrum of frequencies which has been interpreted in terms of Dn resonances together with the electron plasma frequency f/sub pe/ and Bernstein-mode resonances in order to determine the electron density and magnetic field strength. The presence of Dn resonances (cylindrical eigenmodes with frequencies proportional to n/sup 1/2/, n=1,2,...) has been predicted for the Io torus on the basis of the classification of the Earth´s ionospheric sounder-stimulated resonances. The magnetic field strength measured by the Ulysses magnetometer confirmed the values found from Dn resonances to within a few percent. We show that the Dn resonances are present in both sounder stimulated spectra and in natural emissions observed by Ulysses during the inbound and outbound part of the trajectory inside the Io torus. The natural emissions (no sounding) have the same frequencies as their sounder-stimulated counterparts. These observations confirm the specific relation between Dn, f/sub pe/ and f/sub ce/ and the upper hybrid relation for the subsidiary resonances Dn+ and Dn-.