COMPARISON OF LORENZ TYPE AND PLASMA FLUID MODELS FOR NONLINEAR-INTERCHANGE-MODE GENERATION OF SHEAR-FLOW

By solving nonlinear fluid model equations, it is shown that the nonli near interchange mode generates shear flow through Reynolds stress, wh ich suppresses fluctuation amplitude substantially. The nonlinear inte raction between vortex motion and shear flew produces a relaxation osc illation. This behaviour is also confirmed by a Lorenz type model with five ordinary differential equations. However, for the same Rayleigh number and Prandtl number (P-r = 1.0), the period of relaxation oscill ation becomes shorter and the amplitude of vortex motion becomes small er.