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Quasigeostrophic turbulence on a beta-plane with a finite deformation radiusis studied nu- merically, with particular emphasis on frequency and combinedwavenumber-frequency do- main analyses. Under suitable conditions, simulationswith small-scale random forcing and large-scale drag exhibit a spontaneousformation of multiple zonal jets. The first hint of wave-like features is seenin the distribution of kinetic energy as a function of frequency; specifically,for progressively larger deformation scales there are systematic departures inthe form of isolated peaks (at progressively higher frequencies) from apower-law scaling. Con- comitantly, there is an inverse flux of kinetic energyin frequency space which extends to lower frequencies for smaller deformationscales. The identification of these peaks as Rossby waves is made possible byexamining the energy spectrum in frequency-zonal wavenumber andfrequency-meridional wavenumber diagrams. In fact, the modified Rhines scaleturns out to be a useful measure of the dominant meridional wavenumber of themodulating Rossby waves; once this is fixed, apart from a spectral peak at theorigin (the steady jet), almost all the energy is contained in westwardpropagating disturbances that follow the theoretical Rossby dispersionrelation. Quite consistently, noting that the zonal scale of the modulatingwaves is restricted to the first few wavenumbers, the energy spectrum is almostentirely contained within the corresponding Rossby dispersion curves on afrequency-meridional wavenumber diagram. Cases when jets do not form are alsoconsidered; once again, there is a hint of Rossby wave activity, though thespectral peaks are quite muted. Further, the kinetic energy scaling infrequency domain follows a -5/3 power-law and is distributed much more broadlyin frequency-wavenumber diagrams

Low frequency modulation of jets in quasigeostrophic turbulence