The notion has become firmly established that since the semiannual harmonic of the solar forcing is substantially larger than the annual harmonic at the equator, coupled ocean-atmosphere processes much more complex than the direct response to the solar forcing must be involved in producing the observed dominance of the annual harmonic in the annual cycle of sea surface temperature (SST) in equatorial oceans. An examination of the direct response to the solar forcing refutes this notion. Instead, it is found that heat storage, which filters the response can easily explain the relative dominance of the annual harmonic over the semiannual harmonic in the equatorial SST. A simple energy balance model is used to examine the relationship between the annual cycles of SST in the tropics and the top of the atmosphere solar forcing. A qualitative fit of the model results to observations is obtained by specifying a slab mixed layer ocean with depth depending on position. However, the simple model is unable to simulate some aspects of the observed SST, including the persistance of the cold tongue in the eastern equatorial Pacific in October and November, the large semiannual variation in the Arabian Sea, and the phase of the annual cycle of SST near 3 degrees N. A more complex model is required to understand the details of these phenomena.
Complete copies of this report are available from:
Center for Ocean-Land-Atmosphere Studies
last update: 1 July 1996
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