A novel subtropical oscillation observed between North Pacific and North Atlantic during boreal summer

Abstract

During the summers of recent decades, a novel Pacific-Atlantic seesaw/oscillation (PASO) is identified as the dominant mode of the sea level pressure (SLP) anomalies over the northern subtropical region of 110°E–30°W, 10°–30°N. It features prominent interannual variability with remarkable out-of-phase SLP variations between the subtropical Pacific and Atlantic Oceans, respectively. And the PASO, which is only notable in the lower-level troposphere, is mainly induced by the north tropical Atlantic (NTA) sea surface temperature (SST) anomalies. The main physical process is that NTA warming (cooling) can enhance (weaken) the local convection and modulate the northern subtropical Walker cell-like circulation between Pacific and Atlantic. The latter can induce the anomalous sinking (ascending) motion and decrease (increase) convective activities over the central Pacific. As the Gill response to the out-of-phase convection anomalies over the Atlantic and Pacific, respectively, the out-of-phase circulation anomalies come into being over the northwestern flank of the two heating. Moreover, the sustainable development of the summer NTA SST anomalies can be traced back to the preceding early-spring. So a robust cross-seasonal linkage between summer PASO and preceding early-spring NTA SST anomalies can be obtained, suggesting that the summer PASO is predictable. This study provides a new insight to the ongoing hot debate on the interplay of Pacific-Atlantic climate, and highlights the important role of the NTA SST anomalies in simulating the summer PASO, which could provide a meaningful implication for interannual predictions of the western North Pacific climate environments.