  The inverse cascade of magnetic energy occurs when helicity or rotational
instability exists in the magnetohydrodynamic (MHD) system. This well known
phenomenon has been considered as a basis for the large scale magnetic field in
universe. However nonhelical magnetic energy in a decaying MHD system also
migrates toward the large scale, which holds vital clues to the origin of large
scale magnetic field in a quiescent astrophysical system. Zeldovich's rope
dynamo model is considered as a basic and symbolistic model of magnetic field
amplification. However, the rope model assuming specific external forces like
buoyancy or Coriolis force is not appropriate for a decaying turbulent system
without any external force. So we suggest a new dynamo model based on magnetic
induction equation excluding a forcing source. This model shows the expansion
and growth of magnetic field (flux) is basically the redistribution of energy
in the system. The transfer of magnetic energy is in fact a successive
induction of magnetic field resulted from the interaction between the fluid
motion and seed magnetic field. We also discuss about an analytic theorem based
on the scaling invariant MHD equation.
