资源环境科技发展态势分析平台

The decay time of El Nino events is considered to be an important factor in determining whether or not the northern tropical Atlantic (NTA) warming occurs in boreal spring of El Nino decaying years. Through coupled model experiments with different types of sea surface temperature anomalies specified in the tropical Pacific domain, the present study illustrates that the NTA warming is larger and more persistent during slow than fast decaying El Nino events. The amplitude of El Nino events is shown to be another important factor in the difference of the spring NTA warming between slow and fast decaying El Nino events. The NTA warming difference is mainly attributed to the wind speed-related latent heat flux difference in preceding winter according to the model simulations and the observations. The differences of NTA wind and SST variations between slow and fast decay El Nino simulations are mostly consistent with the observations.

Plain Language Summary Previous studies have shown that the northern tropical Atlantic Ocean is warmer in boreal spring of slow decaying El Nino events, but not following El Nino events that end before March. The difference suggests a critical effect of the El Nino decay time. The observed El Nino events show differences not only in the decay time but also in the amplitude of tropical Pacific sea surface temperature anomalies. The present study shows that the difference in the El Nino amplitude is comparably important as the difference in the El Nino decay time in leading to warmer northern tropical Atlantic Ocean in spring. The El Nino amplitude affects the intensity of wind anomalies over the North Atlantic Ocean and thus the magnitude of surface wind speed and latent heat flux anomalies in the northern tropical Atlantic region during boreal winter. The latent heat flux difference in turn leads to the spring sea surface temperature difference in the northern tropical Atlantic region. The present results based on model simulations are mostly consistent with the observations regarding the differences of wind and SST variations in the northern tropical Atlantic region between slow and fast decay El Nino events.