A NUMERICAL EXPERIMENT ON 2-DIMENSIONAL DECAYING TURBULENCE ON A ROTATING SPHERE

A series of numerical experiments on the decaying two-dimensional turbulence is performed for a nondivergent barotropic fluid on a rotating sphere by using a high-resolution spectral model with a triangular truncation of T85. Temporal variations of the total kinetic energy, the total enstrophy, and the enstrophy dissipation rate are found to be influenced by both the spherical geometry and the rotation rate. The energy spectrum is different from that in the beta-plane experiments with Cartesian geometry. Morphology of streamfunction and vorticity fields is investigated for several rotation rates. In nonrotational cases, isolated coherent vortices emerge in the course of time development as in the planar 2D turbulence. As the rotation rate increases, however, the temporal evolution of the flow field changes drastically, and an easterly circumpolar vortex appears in high latitudes. The flow field is then anisotropic in all the latitudes and elongated in the longitudinal direction. Temporal evolution of the flow field is characterized by Rossby wave motions.