ENSO forced and local variability of North Tropical Atlantic SST: model simulations and biases
Remote forcing from El Niño-Southern oscillation (ENSO) and local ocean–atmosphere feedback are important for climate variability over the North Tropical Atlantic. These two factors are extracted by the ensemble mean and inter-member difference of a ten-member Pacific Ocean-Global Atmosphere (POGA) experiment, in which sea surface temperatures (SSTs) are restored to the observed anomalies over the tropical Pacific but fully coupled to the atmosphere elsewhere. POGA reasonably captures main features of the observed North Tropical Atlantic variability. Both ENSO forced and local North Tropical Atlantic Modes (NTAMs) develop with wind-evaporation-SST feedback. Notable biases exist. The seasonality of the simulated NTAM is delayed by 1 month, due to the late development of the North Atlantic Oscillation (NAO) in the model. This suggests the importance of NAO in setting the seasonality of NTAM and of the extratropical-tropical teleconnection. The simulated NTAM is closely related to the Atlantic Niño in the subsequent summer, a relationship not so obvious in observations. Local variability, represented by the preseason NAO and SST persistence, contributes considerably to NTAM variability. Including these two indicators, together with ENSO, improves the predictability of NTAM. The South Tropical Atlantic Mode can be forced by ENSO, and a cross-equatorial dipole is triggered by ENSO instead of local air-sea coupling within the tropical Atlantic.
KeywordsNorth Tropical Atlantic ENSO forcing Local variability
This work is supported by National Science Foundation of China (41606008 and 41521091), the National Basic Research Program of China (2012CB955600), NOAA Climate Program Office (NA13OAR4310092), the Postdoctoral Science Foundation of China (2015M581016), the Fundamental Research Funds for the Central Universities (2015NT07), and YK is supported by Japan Society for the Promotion of Science through Grant-in-Aid for Young Scientists (A) 15H05466 and Japan Science and Technology Agency through Belmont Forum CRA “InterDec”.
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