HR: 17:30h
AN: SH34A-07    [Abstracts]
TI: Characteristics of Langmuir electric field waveforms and power spectra exhibiting nonlinear behavior in Earth's foreshock
AU: * Sigsbee, K
EM: kristine-sigsbee@uiowa.edu
AF: University of Iowa, Department of Physics and Astronomy, 203 Van Allen Hall, Iowa City, IA 52242 United States
AU: Kletzing, C A
EM: craig-kletzing@uiowa.edu
AF: University of Iowa, Department of Physics and Astronomy, 203 Van Allen Hall, Iowa City, IA 52242 United States
AU: Gurnett, D A
EM: donald-gurnett@uiowa.edu
AF: University of Iowa, Department of Physics and Astronomy, 203 Van Allen Hall, Iowa City, IA 52242 United States
AU: Pickett, J S
EM: pickett@uiowa.edu
AF: University of Iowa, Department of Physics and Astronomy, 203 Van Allen Hall, Iowa City, IA 52242 United States
AU: Balogh, A
EM: a.balogh@ic.ac.uk
AF: Imperial College, Space and Atmospheric Physics Group, The Blackett Laboratory, Prince Consort Road, London, SW7 2BW United Kingdom
AU: Lucek, E
EM: e.lucek@ic.ac.uk
AF: Imperial College, Space and Atmospheric Physics Group, The Blackett Laboratory, Prince Consort Road, London, SW7 2BW United Kingdom
AB: The characteristics of Langmuir waves observed by the Cluster WBD Plasma Wave Receiver in Earth's foreshock region are presented with respect to nonlinear wave behavior. Our previous work on waves in the foreshock has shown that the electric field amplitude probability distributions for Langmuir waves observed by Cluster can follow a combination of the log-normal statistics predicted by stochastic growth theory and power law statistics. Power law deviations from log-normal statistics are often the result of spatial averaging, but can also be found for large amplitude waves near the edge of the foreshock, which may show evidence of nonlinearity. This raises questions about the possible effects of nonlinear processes on the amplitude statistics. We examine the significance of nonlinear processes in the foreshock by considering the various types of Langmuir wave power spectra observed in this region. Far away from the foreshock boundary, Langmuir waves have been observed to shift up and down in frequency from the local plasma frequency. Evidence for nonlinear processes such as parametric decay, has also been found in Earth's foreshock in the form of wave spectra with double peaks near the plasma frequency. For selected cases, we discuss the occurrence rates of these types of Langmuir wave spectra for different solar wind conditions and the possible influence of the associated physical processes on the amplitude probability distributions.
DE: 7839 Nonlinear phenomena
DE: 7868 Wave/wave interactions
DE: 2154 Planetary bow shocks
DE: 2159 Plasma waves and turbulence
DE: 2784 Solar wind/magnetosphere interactions
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2004 AGU Fall Meeting