Observed Decadal Midlatitude and Tropical Atlantic Climate Variability

Two common indicators of Atlantic climate variability, viz., the North Atlantic oscillation (NAO) and the crossintertropical convergence zone (ITCZ) sea surface temperature (SST) gradient, are examined for their frequency characteristics and midlatitude-tropical links. SST anomalies north and south of the ITCZ are found to be uncorrelated on all time scales, while the sea level pressure (SLP) fluctuations associated with the NAO display a coherent seesaw between Iceland and the Azores. This out-of-phase relationship spans a broad range of time scales, but is particularly strong in the 5 10 year period band. Strong, broadband coherence between the NAO and the tropical Atlantic crossITCZ SST difference is found in the 8-20 year period band, suggesting a significant midlatitude-tropical interaction. Moreover, tropical Atlantic SSTs on both sides of the ITCZ, separately, exhibit significant coherence with the NAO index and SLP variability over Iceland and the Azores. Based on these findings we hypothesize that the tropical Atlantic (TA) ocean-atmosphere interaction is affecting North Atlantic climate variability.