NEGATIVE VISCOSITY FOR ROSSBY-WAVE AND DRIFT-WAVE TURBULENCE

The possible occurrence of a ''negative viscosity effect'' is studied for Rossby wave and drift wave turbulence. It is assumed that (i) the space and time scales of the wave field are much smaller than the scal es of the mean field, and (ii) the small-scale field is sufficiently w eak, stationary, and maintained by an external source. Such a formulat ion is fruitful for studying the effects (characterized by the effecti ve viscosity) of smaller-scale motions upon larger-scale ones. The cri teria of large-scale instability due to the negative effective viscosi ty are derived for the coherent wave motions as well as for small-scal e isotropic wave turbulence. (C) 1998 American Institute of Physics.