  Local analysis of the two dimensional Navier-Stokes equations is used to
obtain estimates on the energy and enstrophy fluxes involving Taylor and
Kraichnan length scales and the size of the domain. In the framework of zero
driving force and non-increasing global energy, these bounds produce sufficient
conditions for existence of the direct enstrophy and inverse energy cascades.
Several manifestations of locality of the fluxes under these conditions are
obtained. All the scales involved are actual physical scales in R^2 and no
homogeneity assumptions are made.
