Io control of jovian radio emission

Abstract

The stimulation by Io of some fraction of the jovian decametre-wavelength radio emission was recognized in 1964¹. Since then many observations have indicated that strong Io control is limited to frequencies between about 22 and 40 MHz (refs 2–4). At lower frequencies, that is 8–10 MHz, the degree of Io modulation declines markedly⁵. Recent low-frequency RAE 1 satellite⁶, Voyager 1 (ref. 7), and groundbased⁸ studies have shed some doubt on the conclusion that Io control predominates only at high frequencies. Data from the Earth-orbiting RAE 1 satellite⁶ revealed a strong dependence of emission detection probability on Io orbital phase at frequencies in the range 6.5–2.2 MHz. These apparently conflicting results lead to two different conclusions: (1) Io control decreases markedly in the 10–20 MHz regime but reappears near 6 MHz, or, (2) observations above 8 MHz require⁵ that the emission intensity be taken into account. We demonstrate here that the latter is the case and offer a reinterpretation of these data which is consistent with the recent low-frequency satellite and groundbased results.