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A TURBULENCE MODEL FOR THE SOLAR WIND: APPLICATION OF THE TURBULENT MAGNETOHYDRODYNAMIC RESIDUAL-ENERGY EQUATION

Nobumitsu Yokoi
Institute of Industrial Science, University of Tokyo 4-6-1, Komaba, Meguro-ku, Tokyo 153-8505, Japan

Fujihiro Hamba
Institute of Industrial Science, University of Tokyo Komaba, Meguro-ku, Tokyo 153-8505, Japan

Abstrakt

A turbulence model based on a statistical analysis of magnetohydrodynamic (MHD) turbulence with the flow-expansion effects incorporated is applied to the solar wind. In the model, the dynamics of the turbulent MHD residual energy (difference between the kinetic and magnetic energies) and the turbulent cross helicity (velocity−magnetic-field correlation) are simultaneously solved with those of the turbulent MHD energy and its dissipation rate. The observed radial behaviors of the solar-wind turbulence, i.e., the decay of the cross helicity and the stationariness of the Alfvén ratio (rA, the ratio of kinetic to magnetic-field energies) are reproduced by a numerical simulation of the model. The stationary value of rA ~ 0.5 far from the Sun is elucidated as a stationary solution of the turbulence model.