The influence of fluctuation fields on the force-free field. II. The local expansion (Q1058920)

In paper I [the author, ibid. 85, 351-360 (1982; Zbl 0543.76061)], we discussed the influence of fluctuation fields on the force-free field for the case of conventional turbulence and demonstrated the general relationships. In the present paper, by using the approach of local expansion, the equation of average force-free field is obtained as \((1+b)\nabla \times B_ 0=(\alpha +a)B_ 0+a^{(1)}\times B_ 0+K\). The average coefficients \(a,a^{(1)},b\), and K show the influence of the fluctuation fields in small scale on the configurations of magnetic field in large scale. As the average magnetic field is no longer parallel to the average electric current, the average configurations of force-free fields are more general and complex than the usual ones. From the view point of physics, the energy and momentum of the turbulent structures should have influence on the equilibrium of the average fields. Several examples are discussed, and they show the basic features of the fluctuation fields and the influence of fluctuation fields on the average configurations of magnetic fields. The astrophysical environments are often in the turbulent state, the results of the present paper may be applied to the turbulent plasma where the magnetic field is strong.