SOUNDER STIMULATED D(N) RESONANCES IN JUPITER IO PLASMA TORUS

On February 8, 1992, the Ulysses spacecraft passed through Jupiter's Io plasma torus, where rich spectra of narrow-band resonances were stimulated by the relaxation sounder of the Ulysses unified radio and plasma wave (URAP) instrument. Since the gyrofrequency f(g) is comparable to the plasma frequency f(p) in the Io torus, it was predicted that the general classification of stimulated ionospheric D(n) resonances, developed for 1 less-than-or-equal-to f(p)/f(g) le ss-than-or-equal-to 8 in the Earth's topside ionosphere, should apply in the Io torus as well as the Earth's magnetosphere (Osherovich, 1989). The URAP plasmagrams (sounder spectra) in the portions of the Io torus satisfying these plasma conditions are dominated by the D(n) resonances for frequencies below f(p). On most of these plasmagrams the f(p) resonance is also present, but it is seldom the dominant resonance. Neither upper hybrid nor f(p) resonances have been found on these plasmagrams. The identification of D(n) resonances has allow ed both the electron density and the magnetic field amplitude to be calculated. The derived densities on the outbound pass agree well with a Voyager model of Bagenal (1992). The derived magnetic field values are close to the Goddard Space Flight Center O6 magnetic field model.