Zonal flow generation by parametric instability in magnetized plasmas and geostrophic fluids

Two-dimensional magnetized plasmas and geostrophic fluids exhibit a common nonlinearity due to the advection of vorticity. It is shown here that due t o this nonlinearity, the propagation of small scale wave packets is accompa nied by instability of a low frequency, long wavelength component. This ins tability is the coherent hydrodynamic generalization of the resonant type m ean flow instability identified recently [P. H. Diamond, M. N. Rosenbluth, F. L. Hinton, M. Malkov, J. Fleischer, and A. Smolyakov, 17th IAEA Fusion E nergy Conference, IAEA-CN-69/TH3/1, Yokohama, 1998 (to be published, Intern ational Atomic Energy Agency, Vienna)]. The mechanism discussed here, along with the resonant type, constitutes the "hydrodynamic" and "kinetic" regim es of the same process, similar to the case of plasma-beam instabilities. I t is suggested that this generic mechanism is responsible for the generatio n of mean flow in atmospheres of rotating planets and magnetized plasmas. ( C) 2000 American Institute of Physics. [S1070-664X(00)03605-3].