5:30 PM - 5:45 PM
[PCG32-09] Mechanism for the formation of equatorial superrotation in forced shallow-water turbulence with Newtonian cooling
Keywords:Jupiter, zonal pattern, forced shallow-water turbulence, equatorial superrotation, Newtonian cooling, Hough mode
The purpose of the present study is to elucidate the mechanism of the robust formation of equatorial superrotation reported by Scott and Polvani (2008). It is shown that the Newtonian cooling term distorts the structure of the Hough modes. This distortion can be visualized as either the westward or eastward tilting of the equiphase line with increasing the absolute value of latitude; the structural change of the Hough modes leads to the acceleration of the zonal-mean flow. A statistical analysis based on a weak-nonlinear theory predicts that stochastically excited Hough modes generate a prograde equatorial jet, the profile of which is quantitatively consistent with that of the ensemble-averaged zonal-mean flow obtained in nonlinear time-evolutions. The predicted prograde equatorial jet originates mainly from the acceleration produced by Rossby modes, the equiphase line of which is tilted westward by the Newtonian cooling term.
(This work was recently published as Saito and Ishioka (2015))
Scott, R. K. and L. M. Polvani, 2007: Forced-dissipative shallow-water turbulence on the sphere and the atmospheric circulation of the giant planets. J. Atmos. Sci., 64, 3158-3176.
Scott, R. K. and L. M. Polvani, 2008: Equatorial superrotation in shallow atmospheres. Geophys. Res. Lett., 35, L24202.
Saito, I. and K. Ishioka, 2015: Mechanism for the formation of equatorial superrotation in forced shallow-water turbulence with Newtonian cooling. J. Atmos. Sci., in press, now available in Early Online Release form.