The annual cycle of sea surface temperature (SST) in the equatorial Pacific is compared for two simulations with a coupled atmosphere-ocean general circulation model. The simulations differed only in the optical properties of the ocean: Sunlight penetrated below the topmost layer of the ocean model in one case, but was completely absorbed in the top layer in the other. The simulation without the sunlight penetration produced an unrealistic annual cycle of SST with a strong semiannual component in the equatorial Pacific, while the simulation with sunlight penetration was more realistic. The change in the character of the annual cycle resulted from an in crease in the effectiveheat capacity of the ocean associated with an increase in the depth of the mixed layer when sunlight penetration was included. This produced a smaller amplitude of the annual cycle of SST at latitudes close to but off the equator. The zone of intense tropical convection then remained closer to the equator, leading to a reduced semiannual cycle of zonal wind stress at the equator. With the semiannual wind stress forcing reduced, the heat fluxes from the atmosphere became relatively more important, leading to a more realistic annual cycle in SST.
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Center for Ocean-Land-Atmosphere Studies
last update: 27 March 1997
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