Zonal Flow as Pattern Formation: Merging Jets and the Ultimate Jet Length Scale

Abstract

Zonal flows are well known to arise spontaneously out of turbulence. It is shown that for statistically averaged equations of quasigeostrophic turbulence on a beta plane, zonal flows and inhomogeneous turbulence fit into the framework of pattern formation. There are many implications. First, the zonal flow wavelength is not unique. Indeed, in an idealized, infinite system, any wavelength within a certain continuous band corresponds to a solution. Second, of these wavelengths, only those within a smaller subband are linearly stable. Unstable wavelengths must evolve to reach a stable wavelength; this process manifests as merging jets.