Role of north tropical atlantic SST on the ENSO simulated using CMIP3 and CMIP5 models

In this study, role of North Tropical Atlantic (NTA) SST on the ENSO variability is examined with CMIP3 and CMIP5 simulations. It is found that most climate models involved in CMIP3 and CMIP5 successfully simulate the inverse relationship between NTA SST during the boreal spring and the ENSO during the subsequent boreal winter. The multi-model ensemble (MME) results show the observed westward propagating signals related to NTA SST from the Atlantic to the Pacific along the off-equatorial Pacific ITCZ. However, different from the observational argument, the main mechanism for the NTA to induce the ENSO is likely to be different in the MME. While the observational result exhibits the NTA-induced off-equatorial Rossby waves play a more dominant role in leading the Pacific signal, the equatorial wind over the western Pacific related to the NTA-induced Kelvin wave is likely to be more crucial to lead the Pacific variability. In addition, the amplitude of NTA SST-induced ENSO in the MME tends to be systematically weaker, and the preference for the central Pacific SST anomaly is also weak. These weak signals are distinctly improved in a model that simulates two types of El Nino events independently. That the strength of the NTA effect to the Pacific can be affected by the seasonal distribution of climatological precipitation is also discussed. Additionally, the strength of the NTA effect tends to be stronger when the model simulates phase locking of ENSO reasonably.