  At the short times, the enstrophy $\Omega$ of a two-dimensional flow,
generated by a random Gaussian initial condition decays as $\Omega(t)\propto
t^{-\gamma}$ with $\gamma\approx 0.7$. After that, the flow undergoes
transition to a different state characterized by the magnitude of the decay
exponent $\gamma\approx 0.4$ (Yakhot, Wanderer, Phys.Rev.Lett.{\bf 93}, 154502
\~(2004)). It is shown that the very existence of this transition and various
characteristics of evolving flow crucially depend upon phase correlation
between the large-scale modes containing only a few percent of total enstrophy.
