A Cyclotron Theory for the Beaming Pattern of Jupiter’s Decametric Radio Emission

Abstract

Ground-based observations of Jupiter’s decametric radio emission (DAM) have been reviewed by Ellis (1965), Warwick (1967, 1970) and Carr and Gulkis (1969). A startling feature of DAM is the modulating effect of Io, and interpretation of the Io effect has dominated theoretical discussions of DAM until quite recently, specifically until the fly-by s of Voyagers 1 and 2. The Voyager data showed that the DAM appears as nested arcs in the frequency-Jovian longitude plane (Warwick et al. 1979, Boischot et al. 1981). The interpretation of this arc structure has been of primary theoretical interest over the past two years. The most widely adopted explanation is that the emission from each point is confined to the surface of a hollow cone (Goldstein and Thieman 1981). This idea is not new: emission on the surface of a cone was discussed by Ellis and McCulloch (1963); Dulk (1967) derived detailed parameters for the cone (half angle 79° width 1°) from the occurrence pattern of DAM; and Goldreich and Lynden-Bell (1969) presented a theoretical interpretation of it. More recently Goldstein et al. (1979) used observational data on the Jovian magnetic field in deriving properties of the required emission cone. It seems that one requires the properties of the emission cone to vary with position in the Jovian magnetosphere to account for the nested arc pattern (Goldstein and Thieman 1981; Gurnett and Goertz 1981).

Radio emissions from terrestrial planets around white dwarfs

“…The high energy electrons carrying the current produce an auroral footprint in Jupiter's atmosphere (Clarke et al 2002). The energetic electrons also produce radio emissions, via the electron cyclotron maser mechanism, which generates a "hollow-cone" radiation pattern (Hewitt et al 1981). The predicted beaming is consistent with ground and multi-spacecraft observations, which also locate the source near the base of the Io flux tube (Bigg 1964;Dulk 1967;Maeda & Carr 1992;Kaiser et al 2000).…”

Electron Cyclotron Maser Emission near the Cutoff Frequencies

“…This is in contrast to the sharp dependence on 8 of the ellipses for growth in the upper band; this sharp dependence may be regarded as the cause for the growth being restricted to the surface of a hollow cone (see e.g. Hewitt et al 1981 and HMR). As pointed out above, very small values of wpjQe have been excluded from our discussion.…”

“…We believe that the angular dependence of the maser operating at kcjw ::;:j 1 can account well for the inferred angular dependence of DAM (Hewitt et al 1981) and that emission at n ~ 1 is not required for DAM. However, refraction may be important in solar microwave spike bursts, which seem particularly favourable for interpretation in terms of loss-cone driven cyclotron maser emission.…”

Electron-Cyclotron Maser Emission During Solar and Stellar Flares

“…In the semirelativistic limit i.e. 0 < v 2 /e2 << 1 and m » kzcn , the resonant electrons lie in velocity space on the semicircle with centre (Hewitt et al, 1981) vz/c . kzc/m, vl/c -0 and radius v2 /c2 -(kzc/m) 2 -2(w -ne)/Ae.…”