The spectrum cascade by mode coupling in drift-wave turbulence occurs to larger and smaller values of $\left|\overrightarrow{\mathrm{k}}\right|$ rather than toward lower frequencies. This leads to the dual cascade process; energy cascades to smaller $k$ while enstrophy (square of the vorticity) cascades to larger $k$, analogous to two-dimensional hydrodynamic turbulence. However, the speed of energy condensation to $k=0\mathrm{}$ is much slower than in the hydrodynamic case.

• Received 14 June 1978

DOI:https://doi.org/10.1103/PhysRevLett.41.1470