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

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

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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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