Atmospheric electrification in dusty, reactive gases in the solar system and beyond

Detailed observations of the solar system planets reveal a wide variety of local atmospheric conditions. Astronomical observations have revealed a variety of extrasolar planets none of which resembles any of the solar system planets in full. Instead, the most massive amongst the extrasolar planets, the gas giants, appear very similar to the class of (young) Brown Dwarfs which are amongst the oldest objects in the universe. Despite of this diversity, solar system planets, extrasolar planets and Brown Dwarfs have broadly similar global temperatures between 300K and 2500K. In consequence, clouds of different chemical species form in their atmospheres. While the details of these clouds differ, the fundamental physical processes are the same. Further to this, all these objects were observed to produce radio and X-ray emission. While both kinds of radiation are well studied on Earth and to a lesser extent on the solar system planets, the occurrence of emission that potentially originate from accelerated electrons on Brown Dwarfs, extrasolar planets and protoplanetary disks is not well understood yet. This paper offers an interdisciplinary view on electrification processes and their feedback on their hosting environment in meteorology, volcanology, planetology and research on extrasolar planets and planet formation

Cyclotron acceleration of radiation belt electrons by whistlers

The work considers the non linear scattering of energetic electrons in the earth's radiation belts due to cyclotron interaction with VLF whistlers. In particular we consdier the acceleration of electrons which may result from trapping in the inhomogeneous medium. It is shown that considerable electron heating may result, and that the very anisotorpic electron distribution functions observed by Bell etal may be explained

VLF emission triggering by a highly anisotropic electron plasma

A recent paper by Bell et al (Bell et al,2000) reports observations from the POLAR spacecraft of highly anisotropic hot electron distribution functions in the equatorial region of the magnetosphere at L=3.4. The particle instrument HYDRA measures electron fluxes from 1-20 keV. VLF emissions triggered by pulses from Omega (Norway) are found to coincide with 'pancake' type electron distributions with average pitch angles >70 degrees, such distributions being effectively confined to the equatorial zone. We examine the linear and non linear wave particle interaction process between pancake distributions and CW ducted VLF signals. It is concluded that the pitch angle range 67-76 degrees dominates the interaction process, and that with in duct wave saturation amplitudes of 6pT strong non linear trapping occurs for these particles. It is difficult to avoid the impression that highly anisotropic pitch angle distributions don’t have a great effect on resonant particle dynamics. High anisotropy has raised the pitch angle of maximum non linear contribution from 61->72 degrees, and reduced particle non linearity somewhat, in that the onset of trapping occurs at 2pT rather than 1.6pT. Using this data a 1D Vlasov Hybrid Simulation (VHS) VLF code was run to numerically simulate risers triggered by a 1 s Omega pulse. The VHS algorithm defines a time varying phase space simulation box covering the trans-equatorial nonlinear trapping region and a segment of parallel velocity space centred on the local resonance velocity. The simulation particles have F defined as a constant on their trajectories by Liouville's theorem. At each time step F is interpolated from the particles onto the fixed phase space grid, allowing resonant particle current to be calculated. The VHS method is extremely efficient since at each step particles leaving the phase box are discarded, and fresh particles are embedded into the phase fluid where the latter flows into the phase box. Successful numerical triggering of emissions by Omega is shown, and examples of risers, fallers and hooks are shown. The integrated linear trans-equatorial amplification of ~10dB agreed well with figures calculated by Bell from HYDRA data. These successful simulations of Omega emissions with highly anisotropic distribution functions confirm that non linear trapping of cyclotron resonant electrons in the geomagnetic field is the root plasma physical mechanism behind the triggering of VLF emissions

Cyclotron amplification of whistler-mode waves: a parametric study relevant to discrete VLF emissions in the earth's magnetosphere

We study the non linear amplification of VLF waves in the earth's magnetosphere. Particular attention is paid to zero order distribution functions of electrons in which there is a sharp step with respect to parallel velocity. It is shown that such steps strongly favour both the linear and non linear amplification processes. The results obtained are discussed in the light of recent observations of VLF emissions, particularly those of Bell and co workers at Stanford University

Highly anisotropic distribution of energetic electrons and triggered VLF emissions

The work considers the highly anisotropic electron distribution functions observed by Bell and co-workers at Stanford in the magnetosphere. IOt is maintained that Bells' observations provide evidence for the existence of step like deformations in electron distribution function, and that his observations may be due to such steps. The origin of such steps at the top of hiss band emissions is explained, and the implications for triggering of emissions and chorus is explained