Results of high-resolution, long-time numerical integrations of the unforced shallow-water equations on a rotating sphere are presented. A new accurate and efficient grid point method is used for these simulations, that allows to easily reach very high spatial resolutions (up to an equivalent T680 spectral truncation). It is found that, for small values of the Rossby deformation radius LD, the final quasi-steady states of the free evolution are characterized by the formation of robust westward (retrograde) equatorial jets, whose strengths and widths depend on LD and on the rotation speed. It is also shown that the presence of a westward equatorial jet is related to the global prevalence of anticyclonic vorticity.

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