HR: 0800h
AN: SH51B-1208    [Abstracts]
TI: The characteristics of Langmuir waves in the Earth's electron and ion foreshocks: evidence for nonlinear interactions and other physical processes
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: Lucek, E
EM: e.lucek@imperial.ac.uk
AF: Imperial College, Space and Atmospheric Physics Group, The Blackett Laboratory, Prince Consort Road, London, SW7 2BW United Kingdom
AU: Kucharek, H
EM: kucharek@atlas.sr.unh.edu
AF: University of New Hamshire, Space Science Center, Morse Hall, 39 College Rd., Durham, NH 03824 United States
AU: Fazakerley, A
EM: anf@mssl.ucl.ac.uk
AF: Mullard Space Science Laboratory, Holmbury St. Mary , Dorking, RH5 6NT United Kingdom
AU: Eastwood, J P
EM: Jonathan.P.Eastwood.1@gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Laboratory for Solar and Space Physics, Greenbelt, MD 20771 United States
AB: The characteristics of the Langmuir waves observed by the Cluster WBD Plasma Wave Receiver in different regions of the Earth's foreshock are presented. Foreshock Langmuir wave amplitude probability distributions can follow a combination of the log-normal statistics predicted by stochastic growth theory and power law statistics. Power law statistics often result from spatial averaging, but can also be found for large amplitude waves near the foreshock edge. This raises questions about the types of Langmuir wave behavior found in different regions of the foreshock. We will examine the significance of nonlinear interactions and other physical processes in the foreshock by considering the properties of Langmuir wave power spectra. Evidence for parametric decay has been found in the Earth's foreshock in the form of wave spectra with double peaks near the plasma frequency. Far downstream from the boundary between the foreshock and solar wind, Langmuir waves can shift up and down in frequency from the local plasma frequency. In the ion foreshock, waves near the plasma frequency appear to be influenced by ULF waves that cause variations in the local plasma density. Density gradients may cause mode conversion and the reflection of Langmuir waves. For selected cases, we will present the occurrence rates of these types of wave behavior in different regions of the foreshock. The thresholds for nonlinear processes in the foreshock will also be discussed.
DE: 2139 Interplanetary shocks
DE: 2154 Planetary bow shocks
DE: 2772 Plasma waves and instabilities (2471)
DE: 2784 Solar wind/magnetosphere interactions
DE: 7868 Wave/wave interactions
SC: SPA-Solar and Heliospheric Physics [SH]
MN: Fall Meeting 2005