The Relative Importance of Tropical Variability Forced from the North Pacific through Ocean Pathways

In this study we investigate how tropical Pacific SSTs are affected by extratropical atmospheric variability indirectly through oceanic bridges, the Subtropical Cells (STCs). The STCs are wind-driven shallow meridionally overturning circulations that provide a pathway between the extratropical atmosphere and the equatorial upper ocean. Recent observational studies suggest that, in the Pacific Ocean, these cells have been slowing down since the 1970's, reducing the amount of water that upwells at the equator, increasing equatorial SSTs.

In this modeling study we assess the significance of STC-forced tropical ENSO and decadal variability relative to internal tropical decadal variability and also to that forced through atmospheric teleconnections from the extratropics. We will present results from a series of focused intermediate coupled model experiments that isolate the STC-forced change in tropical variability, as well as, the resultant change in atmospheric teleconnections forced from the Tropics. The dependence of STC-forced tropical variability on whether the wind forcing comes from the North or South Pacific will be discussed.