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

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

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

4. upstreamdownstream temperature anisotropy shock (nT) time (s) (I)(II) 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 (a)- 10 s observations (b)- 2 s observations (c)- z-aligned current tube simulation (I) : AIC waves (alpha, p)

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

7. Interpretation of the observations : Anisotropy relaxation : Collapse of the Alfvén wave and tubes generation as a result of Filamentation Instability. AIC generation 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).

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

9. Dynamic of the front equilibriuminstability For  wave front distort 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.