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Transverse instability of Alfven wave : Cluster observations and heuristic explication.

This paper discusses the transverse instability of Alfven waves observed downstream of a quasi-perpendicular shock. It explores the role of temperature anisotropy in wave generation and the collapse of Alfven waves due to the filamentation instability. The observations and theoretical explanations are compared using data from the multi-satellite Cluster mission.

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Transverse instability of Alfven wave : Cluster observations and heuristic explication.

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  1. Summer school - Chalkidiki September 23-28 2003 Transverse instability of Alfven wave : Cluster observations and heuristic explication. Olga Alexandrova LESIA, Observatoire de Paris, France.

  2. Earth Bow Shock B For : Alfven waves (Alfven-Ion-Cyclotron waves, AIC) are widely observed downstream of the quasi-perpendicular shock. Temperature Anisotropy with respect to B is a source of the waves.

  3. 31/03/2001; relative positions of C1, C2, C4 to C3 for the 1st shock crossing : Shock plane n B Observations (multi-satellite Cluster)

  4. shock (II) (I) (nT) (nT) downstream upstream temperature anisotropy time (s) Magnetic field waveforms around the shock crossing in NML-frame : Time origin is the shock crossing time 18:02:17 UT

  5. Dynamic spectrogram (Wavelet transforms of Bn) (II) : Field aligned current tubes • - 10 s observations • - 2 s observations • - z-aligned current tube simulation (I) : AIC waves (alpha, p)

  6. 4 Cluster spacecraft : region (I) plane perpendicular to B In the plasma rest frame: region (II)

  7. Interpretation of the observations : AIC generation Collapse of the Alfvén wave and tubes generation as a result of Filamentation Instability. Filamentation Instability of Alfven wave, observed before in Hall-MHD simulations D. Laveder, T. Passot & PL Sulem, Phys. Plasmas, 9 , 293-304 and 9 , 305-314 (2002). Anisotropy relaxation :

  8. Filamentation of finite amplitude Alfven waves : heuristic explication D. Laveder, these Local longitudinal fluctuations : Alfven wave phase velocity is a local Alfven velocity of the medium : Initial wave front

  9. Dynamic of the front equilibrium instability wave front distort For b>1 Initial wave front

  10. Conclusions 1) The finite amplitude Alfven wave and the resulting filaments are observed downstream of the bow shock; the possible interpretation is Filamentation Instability. 2) Filamentation instability seems to play a role in the final thermalization. 3) Thanks to the 4 satellites of Cluster, parameters and behaviour of the observed structures are obtained, that gives a possibility to compare the observations with the theory.

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