ECH Wave Dispersion – The Effects of Suprathermal Electron Distributions

Using experimental wave and particle data from GEOS I, detailed modelling of weak dayside cyclotron harmonic waves shows several features of interest. The predicted temporal growth rates and inferred spatial amplification are very low - as observed. This event is contrasted with a similar study of a strong sporadic event which occurred in the same local time sector and the significance of the differences in the low energy and “free” energy components of the electron velocity distributions are evaluated and discussed

Source of saturnian myriametric radiation

The Voyager 1 and 2 flybys of Saturn revealed the presence of a variety of plasma waves associated with Saturn's magnetosphere1,2, some electrostatic in nature, others apparently electromagnetic. Possibly the most unambiguous identification of the latter in the low-frequency range (< 10 kHz) is of narrow-banded emissions observed over a 3-day period when Voyager 1 was outbound3. Persistent bands of emission near 5 kHz were seen from 19 to 58 Rs (where Rs is Saturn's radius = 60,330 km), and, as the plasma parameters varied widely along the trajectory over this range, it is difficult to envisage how these emissions could be anything but freely-propagating electromagnetic waves. Hitherto their source was unknown, but similar emissions have been observed within the magnetospheres of Jupiter4 and Earth5–7 and, based on our knowledge of the latter in particular, it is proposed here that the source of the saturnian narrow-band emissions lies in electrostatic upper-hybrid waves near the equatorial plane just beyond the orbit of the moon Rhea

Amplitude variations of electron cyclotron harmonic waves

Electron cyclotron harmonic (ECH) instabilities just outside the plasmapause and at frequencies near the cold upper hybrid frequency are a common feature of the Earth\u27s magnetosphere. These waves which have virtually no magnetic component, are believed to have an important role in the generation of weak diffuse aurora1,2. They are able to interact strongly with electrons in the hundred eV to several keV energy range which can result in pitch angle scattering and precipitation on magnetic field lines which map down into the auroral zone. On the dayside magnetosphere these waves can exhibit large amplitude variations of 30–40 dB and can also exist at steady amplitudes on time scales of the order of tens of seconds. Here we seek an explanation for the sporadic nature of such instabilities by performing linear stability calculations and extending the technique used in the accompanying paper3