  We studied dynamical balances in magnetorotational instability (MRI)
turbulence with a net vertical field in the shearing box model of disks.
Analyzing the turbulence dynamics in Fourier (${\bf k}$-)space, we identified
three types of active modes that define turbulence characteristics. These modes
have lengths similar to the box size, i.e., lie in the small wavenumber region
in Fourier space labeled the vital area and are: (i) the channel mode - uniform
in the disk plane with the smallest vertical wavenumber,(ii) the zonal flow
mode - azimuthally and vertically uniform with the smallest radial wavenumber
and (iii) the rest modes. The rest modes comprise those harmonics in the vital
area whose energies reach more than $50 \%$ of the maximum spectral energy. The
rest modes individually are not so significant compared to the channel and
zonal flow modes, however, the combined action of their multitude is dominant
over these two modes. These three mode types are governed by interplay of the
linear and nonlinear processes, leading to their interdependent dynamics. The
linear processes consist in disk flow nonmodality-modified classical MRI with a
net vertical field. The main nonlinear process is transfer of modes over
wavevector angles in Fourier space - the transverse cascade. The channel mode
exhibits episodic bursts supplied by linear MRI growth, while the nonlinear
processes mostly oppose this, draining the channel energy and redistributing it
to the rest modes. As for the zonal flow, it does not have a linear source and
is fed by nonlinear interactions of the rest modes.
