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The origin of Pacific-South America patterns
Daeho Jin, George Mason University, Fairfax, VA; and B. P. Kirtman
The “Pacific-South American (PSA)” pattern is known as a major atmospheric response to ENSO in the Southern Hemisphere (SH). Lead-Lag Maximum Covariance Analysis (LLMCA) is used to diagnose the detailed relationship between the tropical Pacific (TP) sea surface temperature (SST) and the SH atmospheric variability. The analysis shows that most of the covariance occurs when the SH leads the TP SST by a few months. A second pattern emerges when the TP SST leads the SH by 3 to 7 months. Model experiments are done with an Atmospheric GCM coupled to a slab mixed layer ocean model. When the TP region is prescribed with idealistic periodic ENSO, the LLMCA shows a strong PSA-like pattern when the TP leads the SH by 0 to 1 months. When the TP region is model using a slab mixed layer ocean, the PSA-like pattern noted above is weak or undetectable in the LLMCA. Both experiments do not have second pattern. Hence the ENSO-SH teleconnection seems to be responsible for PSA-like SH atmosphere pattern, but the role of second pattern is not clear. As an additional experiment, atmospheric GCM with prescribed observed SST was made. The result of the LLMCA is similar to the observational data, but with the difference is that second pattern is weak or undetectable. To sum up, the PSA teleconnection is induced by ENSO and affects SH atmosphere, but the second pattern may not be due to ENSO interaction directly.
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Session 1, Coupled ocean-atmosphere interactions and their contribution to climate variability on all time scales (Part I)
Monday, 20 August 2007, 9:00 AM-10:30 AM, Broadway-Weidler-Halsey
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