WAVE-DISPERSION IN A ROTATING, DIFFERENTIALLY-HEATED FLUID MODEL

An investigation is made of the mechanics of the wave dispersion pheno menon obtained in a numerical simulation of the rotating annulus flow system. Wave dispersion is characterized by the presence of two quasi- steady sideband baroclinic waves of comparable amplitudes and differen t phase speeds, The recurrence of wavepacket formation downstream of t he wave train can be kinematically related to the group velocity, The vertical structure of the temperature wave for the primary wavenumber consists of a upper layer and a lower layer maximum, while the seconda ry wavenumber lacks the lower layer maximum. The primary wave is baroc linically active as it is maintained by the zonal flow baroclinicity, while the secondary wave is baroclinically passive in the sense that i t is linearly stable with respect to the instantaneous zonal flow, alt hough it exhibits a strong baroclinic energy conversion, Wave-wave int eractions enhance the baroclinic energy conversion of the secondary wa ve by increasing the pressure-temperature phase difference, counteract ing the negative nonlinear energy transfer and the stabilizing effect of the zonal mean basic state. (C) 1997 Elsevier Science B.V.