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Session: Magnetohydrodynamics 1
Session starts: Tuesday 25 August, 10:30
Presentation starts: 12:00
Room: Room F

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Romain Meyrand (Observatoire de Paris)
Khurom Kiyani (University of Warwick, UK)
Sébastien Galtier (Université Paris-Sud, France)

Abstract:
Three-dimensional incompressible magnetohydrodynamic (MHD) turbulence with a strong uniform magnetic field b0 may be governed by the regime of weak turbulence. At leading order, it is known that the asymptotic regime of weak MHD turbulence is achieved via three-wave resonant interactions with the scattering of two of these waves on a third/2D mode for which k//=0. For zero cross-helicity, the expected exact solution is an energy spectrum in $k_perp^{-2}$. Higher-order statistics has, however, never been reported in the literature. Therefore, we have recently investigated this question with high resolution direct numerical simulations (Meyrand et al., 2014). We found the presence of strong intermittency when the vector separation of structure functions is taken transverse to b0. This result may be explained by the influence of the 2D modes whose regime belongs to strong turbulence. In addition to shed light on the origin of this intermittency, we derived a log-Poisson law, $\zeta_p = p/8 +1 -(1/4)^{p/2}$, which fits perfectly the data and highlights the important role of parallel current sheets.