Rapid beat generation of large-scale zonal flows by drift waves: A nonlinear generic paradigm

• Published in: Physical review letters 2004-08, Vol.93 (6), p.065004.1-065004.4, Article 065004
• Main Authors: MCCARTHY, D. R, LASHMORE-DAVIES, C. N, THYAGARAJA, A
• Format: Article
• Language: English
• Subjects: Drift waves; Exact sciences and technology; Magnetohydrodynamics (including electron magnetohydrodynamics); Nonlinear waves and nonlinear wave propagation (including parametric effects, mode coupling, ponderomotive effects, etc.); Physics; Physics of gases, plasmas and electric discharges; Physics of plasmas and electric discharges; Plasma dynamics and flow; Waves, oscillations, and instabilities in plasmas and intense beams
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.93.065004

The generalized Charney-Hasegawa-Mima equation is unstable to a four wave modulational instability whereby a coherent, monochromatic drift wave can drive a band of modes and associated zonal flows unstable. Although initially the fastest growing modes dominate, a secondary nonlinear instability later drives the longest wavelength zonal flow and its associated sidebands at twice the growth rate of the fastest growing modulationally unstable modes. This results in a direct transfer from strongly unstable short wavelength modes to the weakly unstable long wavelength modes, which drains the short wavelength pump energy. A related but less efficient direct enstrophy cascade generates very short wavelength modes lying outside the band of modulationally unstable modes.