The role of atmospheric teleconnection in the subtropical thermal forcing on the equatorial pacific

The equatorial response to subtropical Pacific forcing was studied in a coupled climate model. The forcings in the western, central and eastern subtropical Pacific all caused a significant response in the equatorial thermocline, with comparable magnitudes. This work highlights the key role of air-sea coupling in the subtropical impact on the equatorial thermocline, instead of only the role of the “oceanic tunnel”. The suggested mechanism is that the cyclonic (anticyclonic) circulation in the atmosphere caused by the subtropical surface warming (cooling) can generate an anomalous upwelling (downwelling) in the interior region. At the same time, an anomalous downwelling (upwelling) occurs at the equatorward flank of the forcing, which produces anomalous thermocline warming (cooling), propagating equatorward and resulting in warming (cooling) in the equatorial thermocline. This is an indirect process that is much faster than the “oceanic tunnel” mechanism in the subtropical impact on the equator.