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tokens: the limit of weak viscosity and/or magnetic diffusivity is accessible. 5. Naturally all the renormalized coefficients are proportional to D 1 , which is the magnitude of the nonreflectionally symmetric component of the stirring force. It follows that the α -effect is impossible if the turbulence is not helical: . 6. Finally, an interesting observation was made, that in the strong MHD turbulence the energy spectra are substantially influenced by the helical component of the stirring force, whereas the helicity spectrum is determined by both the helical and nonhelical components of the forcing. All the nonlinear corrections to turbulent energy and helicity spectra are at leading order proportional to the energy of the mean magnetic field, which emphasizes its role in the MHD turbulence. A significant limitation of the presented analysis is that the turbulence, i.e., the stirring force, was assumed isotropic. This is a great simplification; however, the natural astrophysical and geophysical flows, in the majority of cases, possess at least one distinguished axis associated with the background rotation, which introduces anisotropy. Application of the renormalization group technique to rapidly rotating MHD flows, in order to obtain a more astrophysically realistic form of the mean EMF (the -tensor), is a subject of current research (see Mizerski 2020 ). Appendix The details of the renormalization procedure applied in order to obtain the mean field equations are given here. First of all, we clarify how the ensemble averaging should be understood and explain the concept of a conditional average over a statistical subensemble for short-wavelength modes. We adopt the approach of McComb et al. ( 1992 ; see also McComb Watt 1990 , 1992 ). The essential idea of this approach is the introduction of a subensemble of flow realizations including near-chaotic statistical properties for the short-wavelength shell , but remaining quasi-deterministic for . The subensemble average can be precisely defined and then, utilizing the assumption that in the turbulent cascade the energy transfer in the Fourier space is local, the following crucial properties can be proved: For details see particularly Section IV and the beginning of Section V in McComb et al. ( 1992 ). We now substitute the expressions for short-wavelength modes from Equations ( 65a ) and ( 65b ) into the conditional averages in the equations for long-wavelength modes in Equations ( 64a ) and ( 64b ). Neglecting higher-order correlations of the type , etc. (which eliminates the rests in Equations ( 65a ) and ( 65b )), and using , , and , one obtains The order of accuracy kept above, i.e., up to terms of the order with neglect of terms 7 7 Recall that this allows for neglect of the terms proportional to and in the rest ( 67b ). in particular, allows us to keep in the two last terms in the Lorentz force ( 127b ); anticipating the results, we may say that these terms account for the Lorentz force effect