HR: 17:30h
AN: SM32D-07    [PDF]
TI: Filamentation of Langmuir waves and the role of absolute decay instability in the electron foreshock: comparison of CLUSTER observations and theory
AU: Soucek, J
EM: soucek@ufa.cas.cz
AF: LPCE/CNRS, 3A, Av. de la recherche scientifique, Orleans, 45071 France
AU: Soucek, J
EM: soucek@ufa.cas.cz
AF: UFA AV CR, Bocni II/1401, Prague 4, 14131 Czech Republic
AU: * Krasnoselskikh, V
EM: vkrasnos@cnrs-orleans.fr
AF: LPCE/CNRS, 3A, Av. de la recherche scientifique, Orleans, 45071 France
AU: Dudok de Wit, T
EM: ddwit@cnrs-orleans.fr
AF: LPCE/CNRS, 3A, Av. de la recherche scientifique, Orleans, 45071 France
AU: Pickett, J
EM: pickett@uiowa.edu
AF: Department of Physics and Astonomy, University of Iowa, Iowa City, IA 52242 United States
AU: Kletzing, C
EM: cak@delta.physics.uiowa.edu
AF: Department of Physics and Astonomy, University of Iowa, Iowa City, IA 52242 United States
AU: Walker, S
EM: simon.walker@sheffield.ac.uk
AF: ACSE, University of Sheffield, Mappin Street, Sheffield, S1 3JD United Kingdom
AU: Sigsbee, K
EM: kristine-sigsbee@uiowa.edu
AF: Department of Physics and Astonomy, University of Iowa, Iowa City, IA 52242 United States
AU: Santolik, O
EM: santolik@mff.cuni.cz
AF: Faculty of Mathematics and Physics, Charles University, V Holesovickach 2, Prague, 18000 Czech Republic
AB: Statistical analysis of HF electric field observed by WBD instrument on CLUSTER in the electron foreshock region show that the distribution of wave amplitudes depends on the scale of their modulation. In many cases the HF spectrum has two distinct narrow peaks near the plasma frequency. In some of those cases, when the difference of frequencies can be resolved by the instrument and is above the lower limit of frequency response, a wave with frequency corresponding to this difference is also observed. These observations indicate the presence of decay instability. The energy distribution has log-normal form for small amplitudes and manifests strong deviations from gaussian form for amplitudes larger than 1 mV/m. This suggests that the properties of small and large amplitude waves are determined by different physical processes. Conventional theory of parametric instabilities in a homogeneous medium gives results independent on scale, that disagrees with these experimental results. We propose a theoretical model based on the hypothesis that the wave activity for relatively intense electric fields is concentrated in filaments directed along the magnetic field lines. In this case the absolute parametric instability can develop. This results in the formation of profiles of the electric field of secondary Langmuir wave and density perturbations associated with ion-sound waves that correspond to eigenmodes generated by this instability. The threshold is shown to be inversely proportional to the characteristic modulation scale. This is due to the effect of the leakage of the energy of secondary waves through the filament boundaries. Taking into account this additional damping we evaluated the dependencies of wave amplitudes on characteristic scale of the modulation in a stationary state. The analytical results are shown to be in a good agreement with statistical analysis of intense Langmuir waves observed by WBD instrument in the electron foreshock region.
DE: 2772 Plasma waves and instabilities
DE: 2784 Solar wind/magnetosphere interactions
SC: SPA - Magnetospheric Physics [SM]
MN: 2003 Fall Meeting