Seasonal evolution of tropical Pacific influence on the tropical North Atlantic: A review of impacts on air-sea interactions

The tropical Pacific (TP) is amongst the regions of remote forcing of tropical North Atlantic (TNA) air-sea interactions. Yet the relationship between the TNA and the TP basin interactions changes with season, in particular with respect to the different seasonal evolutions of El Nino-Southern Oscillation (ENSO) events. For example, whereas during spring a warm winter Pacific ENSO event leads to a weaker Caribbean low-level jet (LLJ) and to a warm TNA-Caribbean Sea, during summer cool ENSO conditions are related to a weaker Caribbean LLJ and warm conditions in the TNA-Caribbean Sea. In this presentation we review recent studies about the various “flavors of ENSO” and discuss them in the context of TNA air-sea interactions leading to summertime TNA climate anomalies. Furthermore, we analyze the constructive and destructive interferences between the tropical Pacific wintertime (indirect) forcing and the summertime (direct) forcing on TNA air-sea interactions during summer. The different seasonal evolutions of tropical Pacific anomalies were obtained from observed Niño3.4 SSTA indexes. Events for which the Niño3.4 index had: 1) an extreme change in sign from winter to summer, or 2) a consistent phase (same sign) from winter to summer were identified. Then composites of relevant TNA atmospheric and oceanic metrics were performed to diagnose and determine the impacts on the summertime TNA. The data used is from coupled climate models (forced in the Pacific) and reanalyses. Contrary to what was expected TNA sea surface temperature (SST) anomalies do not have a cumulative effect (i.e., do not stay warm) for tropical Pacific conditions that change from warm in winter to cool in summer. Yet the summertime TNA low-level winds are modulated by the constructive interference from winter to summer through the role of the Inter-tropical Convergence Zone.