HR: 0800h
AN: SH51C-0290    [Abstracts]
TI: CLUSTER Observations of Langmuir Wave Decay in the Terrestrial Foreshock
AU: * Soucek, J
EM: soucek@ufa.cas.cz
AF: LPCE/CNRS, 3A, Avenue de la Recherche Scientfique, Orleans, 45071 France
AU: * Soucek, J
EM: soucek@ufa.cas.cz
AF: UFA AV CR, Bocni II/1401, Prague, 14131 Czech Republic
AU: Krasnosselskikh, V
EM: vkrasnos@cnrs-orleans.fr
AF: LPCE/CNRS, 3A, Avenue de la Recherche Scientfique, Orleans, 45071 France
AU: Dudok de Wit, T
EM: ddwit@cnrs-orleans.fr
AF: LPCE/CNRS, 3A, Avenue de la Recherche Scientfique, Orleans, 45071 France
AU: Pickett, J
AF: Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242 United States
AB: The parametric decay of Langmuir waves is often proposed as one of the processes saturating the growth of beam-excited Langmuir waves in the Earth's foreshock. We investigated this process by analysis of high frequency electric field data obtained in the foreshock by the WBD instrument of CLUSTER. A typical observed electric field waveform contains a superposition of several waves with frequencies close to $\omega_p$ often accompanied by bursts of weaker ion-acoustic waves at lower frequencies. Such observations are consistent with the three-wave decay if the frequencies of waves satisfy a resonance condition $f_3 = f_2 + f_1$. In this study, we proved by statistical analysis that this condition is satisfied for a large number of observed triple-peaked spectra and that the relative number of such triplets increases with wave amplitude. This finding is consistent with the presumption that the decay instability can only proceed if the wave amplitude exceeds certain threshold and our analysis provides a rough estimate of this threshold value. Since the solar wind plasma is not strictly Maxwellian, but contains a significant supra-thermal component, two types of parametric decay are possible here: the classical one, where a Langmuir wave decomposes into Langmuir and ion-sound waves, or an alternative process, where one of the product waves is an electron-acoustic wave. In this presentation, we bring an experimental argument in favor of the latter alternative.
DE: 7839 Nonlinear phenomena
DE: 7863 Turbulence
DE: 7868 Wave/wave interactions
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2004 AGU Fall Meeting