Whistler mode noise in the inner Jovian magnetosphere

Hat shaped pitch angle distributions of energetic electrons E/sub e/ > 21 MeV in the inner Jovian magnetosphere suggest the existence of a bandlimited spectrum of whistler mode noise phenomenologically similar to the ELF hiss present inside the Earth's plasmasphere. It is shown that for the terrestrial case the upper cutoff frequency of the ELF hiss is related via the first order cyclotron resonance condition to a ''critical pitch angle feature'' occurring in the pitch angle distributions of energetic electrons. Application of this condition to the pitch angle distributions obtained at L = 3 by Pioneer 10 to 11 Jupiter observations of energetic electrons E/sub e/ > 21 and >31 MeV yields an estimate of 2.8 approximately less than f/sub c/ approximately less than 4.6 kHz for the upper cutoff frequency of the whistler mode noise. A ray tracing study of whistler mode waves propagating in a model disc-like distribution of plasma suggests that whistler mode wave growth occurs predominantly at or near the Jovian magnetic equator in the region 3 < L < 10. Utilizing Pioneer 10 observations to construct a model anisotropic distribution of energetic electrons, the linear growth rates as a function of frequency are calculated for parallel propagating whistlers generated at the magnetic equator. The frequency above which the growth is negative is taken to be a good estimate for the upper cutoff frequency of the whistler mode noise. Upper cutoff frequencies determined in this manner for the region 3 < L < 10 fall in the vlf range of 5 to 10 kHz