Impact of internal climate variability on the relationship between spring Northern Tropical Atlantic SST anomalies and succedent winter ENSO : the role of the North Pacific Oscillation

Abstract

Previous studies suggested that spring sea surface temperature anomalies (SSTAs) in the northern tropical Atlantic (NTA) have a marked influence on the succedent winter El Niño–Southern Oscillation (ENSO). In this study, we examine the spring NTA SSTA–winter ENSO connection in a 50-member large-ensemble simulation conducted with the Canadian Centre for Climate Modelling and Analysis second-generation Canadian Earth System Model (CanESM2) and a 100-member ensemble simulation conducted with the Max Planck Institute Earth System Model (MPI-ESM). The observed out-of-phase relation of spring NTA SSTA with winter ENSO can be captured by the multimember ensemble means of the large-ensemble simulations from both models. However, the relation shows a large diversity among different ensemble members attributing to the internal climate variability. The preceding winter North Pacific Oscillation (NPO) is suggested to be an important source of the internal climate variability that modulates the spring NTA SSTA–ENSO connection. The modulation of the winter NPO on the subsequent spring NTA SSTA–winter ENSO relation is seen in both climate modeling and observational datasets. When winter NPO and spring NTA SSTA indices have the same (opposite) sign, the linkage between the spring NTA SSTA and the following winter ENSO tends to be weak (strong). The NPO modulates the spring NTA SSTA–winter ENSO relation mainly via changing the zonal wind anomalies over the tropical western-to-central Pacific induced by the spring NTA SSTA. In addition, our analysis indicates that winter NPO may have a marked effect on the predictability of winter ENSO based on the condition of spring NTA SSTA.