Analogous Pacific and Atlantic Meridional Modes of Tropical Atmosphere–Ocean Variability*

Abstract

Abstract From observational analysis a Pacific mode of variability in the intertropical convergence zone (ITCZ)/cold tongue region is identified that possesses characteristics and interpretation similar to the dominant “meridional” mode of interannual–decadal variability in the tropical Atlantic. The Pacific and Atlantic meridional modes are characterized by an anomalous sea surface temperature (SST) gradient across the mean latitude of the ITCZ coupled to an anomalous displacement of the ITCZ toward the warmer hemisphere. Both are forced by trade wind variations in their respective northern subtropical oceans. The Pacific meridional mode exists independently of ENSO, although ENSO nonlinearity projects strongly on it during the peak anomaly season of boreal spring. It is suggested that the Pacific and Atlantic modes are analogous, governed by physics intrinsic to the ITCZ/ cold tongue complex.