Non-boussinesq properties of zonal flows and GAMs

In the presence of non-Boussinesq effects, i.e., a significant parameter variation on turbulence scale lengths, the turbulent modifications of the dispersion relation of the GAMs become important, completely dominate linear dispersive effects and greatly increase the radial group velocities. In the case of an extended region of GAM generating turbulence, propagation of the GAMs rather far away from the point of their base frequency can be observed. In the opposite case only a weak propagation into regions where GAMs are damped occurs. The fact that the turbulence nonlinearly modifies the GAM dispersion relation, can lead to the set-up of completely nonlinear reflection and absorption layers. This allows for complex global mode structures, depending on the variation of the turbulence parameters.