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Detailed Reference Information |
Sauer, K., Dubinin, E., Dunlop, M., Baumgartel, K. and Tarasov, V. (1999). Low-frequency electromagnetic waves near and below the proton cyclotron frequency at the AMPTE Ba release: Relevance to comets and Mars. Journal of Geophysical Research 104: doi: 10.1029/1998JA900143. issn: 0148-0227. |
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Nongyrotropic massloading is a characteristic signature of the AMPTE barium release in the solar wind because of the large pickup radius compared with the size of the interaction region. In the fluid picture this is equivalent to a beam-plasma configuration where the solar wind protons have a large relative velocity to the heavies, which can be considered as unmagnetized. Dispersion analysis on the basis of bi-ion Hall-MHD equations gives that two types of low-frequency electromagnetic waves are excited. The upper instability occurs in the branch of whistler/magnetoacoustic waves with the remarkable feature that the frequency in the beam (spacecraft) frame of the most unstable wave is close to the proton cyclotron frequency. Its growth rate strongly depends on the electron plasma beta (&bgr;e) which preferentially determines the whistler damping at oblique propagation. In consequence, the increase of the growth rate with the propagation angle is limited and an instability gap results at intermediate angles (40¿≤&thgr;≤70¿). For &bgr;e≈1, only small ranges near parallel and transverse propagation remain. For a high beam velocity the lower instability is determined by the cutoff frequency of the bi-ion system. Both lines were clearly seen in the spectra of magnetic field data of the AMPTE Ba release during the transition phase when the Ba ion density decreases below the solar wind density. These results may be relevant for other situations in space: comets with low gas production rates (q≤1028 s-1), nonmagnetized planets (Venus, Mars) and active moons (Phobos, Deimos) including their gas tori. ¿ 1999 American Geophysical Union |
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Abstract |
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Keywords
Space Plasma Physics, Active perturbation experiments, Interplanetary Physics, Plasma waves and turbulence, Space Plasma Physics, Kinetic and MHD theory |
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Publisher
American Geophysical Union 2000 Florida Avenue N.W. Washington, D.C. 20009-1277 USA 1-202-462-6900 1-202-328-0566 service@agu.org |
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