Zonal flow (plasma)

In [magnetic confinement fusion|toroidally confined fusion Plasma (physics)|plasma experiments] the term zonal flow means a plasma flow within a magnetic surface primarily in the poloidal direction. This usage is inspired by the analogy between the quasi-two-dimensional nature of large-scale atmospheric and oceanic flows, where zonal means latitudinal, and the similarly quasi-two-dimensional nature of low-frequency flows in a strongly magnetized plasma.
Zonal flows in the toroidal plasma context are further characterized by

being localized in their radial extent transverse to the magnetic surfaces,
having little or no variation in either the poloidal or toroidal direction—they are m = n = 0 modes,
having zero real frequency when analyzed by linearization around an unperturbed toroidal equilibrium state.
Arising via a self-organization phenomenon driven by low-frequency drift-type modes, in which energy is transferred to longer wavelengths by modulational instability or turbulent inverse cascade.