28 research outputs found
The collective gyration of a heavy ion cloud in a magnetized plasma
In both the ionospheric barium injection experiments CRIT 1 and CRIT 2, a long duration oscillation was seen with a frequency close to the gyro frequency of barium and a time duration of about one second. A model for the phenomena which was proposed for the CRIT 1 experiment is compared to the results from CRIT 2 which made a much more complete set of measurements. The model follows the motion of a low Beta ion cloud through a larger ambient plasma. The internal field of the model is close to antiparallel to the injection direction v sub i but slightly tilted towards the self polarization direction E sub p = -V sub i by B. As the ions move across the magnetic field, the space charge is continuously neutralized by magnetic field aligned electron currents from the ambient ionosphere, drawn by the divergence in the perpendicular electric field. These currents give a perturbation of the magnetic field related to the electric field perturbation by Delta E/Delta B approximately equal to V sub A. The model predictions agree quite well with the observed vector directions, field strengths, and decay times of the electric and magnetic fields in CRIT 2. The possibility to extend the model to the active region, where the ions are produces in this type of self-ionizing injection experiments, is discussed
Magnetosphere-Ionosphere Coupling Through E-region Turbulence: Anomalous Conductivities and Frictional Heating
Global magnetospheric MHD codes using ionospheric conductances based on
laminar models systematically overestimate the cross-polar cap potential during
storm time by up to a factor of two. At these times, strong DC electric fields
penetrate to the E region and drive plasma instabilities that create
turbulence. This plasma density turbulence induces non-linear currents, while
associated electrostatic field fluctuations result in strong anomalous electron
heating. These two effects will increase the global ionospheric conductance.
Based on the theory of non-linear currents developed in the companion paper,
this paper derives the correction factors describing turbulent conductivities
and calculates turbulent frictional heating rates. Estimates show that during
strong geomagnetic storms the inclusion of anomalous conductivity can double
the total Pedersen conductance. This may help explain the overestimation of the
cross-polar cap potentials by existing MHD codes. The turbulent conductivities
and frictional heating presented in this paper should be included in global
magnetospheric codes developed for predictive modeling of space weather.Comment: 13 pages, 5 figures, 2nd of two companion paper
Magnetosphere-Ionosphere Coupling Through E-region Turbulence 1: Energy Budget
During periods of intense geomagnetic activity, strong electric fields and
currents penetrate from the magnetosphere into high-latitude ionosphere where
they dissipate energy, form electrojets, and excite plasma instabilities in the
E-region ionosphere. These instabilities give rise to plasma turbulence which
induces non-linear currents and strong anomalous electron heating (AEH) as
observed by radars. These two effects can increase the global ionospheric
conductances. This paper analyzes the energy budget in the electrojet, while
the companion paper applies this analysis to develop a model of anomalous
conductivity and frictional heating useful in large-scale simulations and
models of the geospace environment. Employing first principles, this paper
proves for the general case an earlier conjecture that the source of energy for
plasma turbulence and anomalous heating equals the work by external field on
the non-linear current. Using a two-fluid model of an arbitrarily magnetized
plasma and the quasilinear approximation, this paper describes the energy
conversion process, calculates the partial sources of anomalous heating, and
reconciles the apparent contradiction between the inherently 2-D non-linear
current and the 3-D nature of AEH.Comment: 13 pages, 1 figure; 1st of two companion paper
Multipulse and double-pulse velocities of Scandinavian Twin Auroral Radar Experiment (STARE) echoes
First VHF auroral radarinterferometer observations
The radar interferometer technique first used at the magnetic equator in Peru is also a very powerful means for studying auroral plasma instabilities. We present here the first results, obtained with a 49.92 MHz, 20-25 KW peak power pulsed radar located in Ithaca, NY (42.5° N, 76.4° W). Strong auroral echoes were obtained during several highly active periods. Phase differences between the signals received on the two antennas accurately determine the E-W position, within the scattering volume, of localized scattering centers, and changes in this phase determine the corresponding velocity. The signal Doppler shift describes radial (essentially N-S) motion. The data provide detailed information on the turbulent structure of the echoing region and show clearly that different features in the Doppler power spectrum often represent signals coming from different locations. If we assume that the radial and transverse phase velocities represent real drift velocities, we can determine full horizontal velocity vectors from the data and hence the horizontal electric field, usually with a time resolution of the order of 15-30s
The Collective Gyration of a Heavy Ion Cloud in a Magnetized Plasma
Invited talk at COASPAR Plenary Meeting 1990.To be published in Advances in Space Research.QC 20120530</p