VARIABLE INTENSITY OF LAGRANGIAN CHAOS IN THE NONLINEAR DYNAMO PROBLEM

The link between the level of chaos of the velocity and the saturation of the dynamo in ABC flows is examined numerically with the full MHD equations at magnetic Reynolds numbers up to 240 and for scale separat ions up to four. In the Latter case, a chaotic dynamo at small scale a nd a large-scale magnetic field develop together. Spatial modification s of the chaotic features of the resulting velocity measured by pdf of finite-time Lyapunov exponents occur in all cases because of both hyd rodynamic and MHD instabilities. Saturation occurs as well with a weak er contrast in magnetic structures. [S0031-9007(98)07723-0].