An Equatorial Diffusive Boundary Layer and the Equatorial Stacked Jets in Thermally Driven OGCMs

Abstract

New equatorial boundary layer solutions are found in a reduced-gravity model with large horizontal diffusivity. Analytical and semianalytical solutions are obtained and the structure of the boundary layer is discussed. The equatorial ?stacked jets? often found in thermally driven coarse-resolution OGCMs are identified as corresponding to these boundary layer solutions. The width of the boundary layer is essentially that of the frictional (Stommel or Munk) boundary layer when the horizontal diffusivity is sufficiently large. The flow of the equatorial boundary layer is primarily a jetlike zonal flow, but there is significant meridional velocity, which has meridional convergence and divergence. The resultant vertical velocity manifests itself as meridional overturning cells that are also often found in OGCMs.