Extratropical Cyclones Act as a “Bridge” to the Concurrent Impact of ENSO on the Arctic Oscillation During Boreal Winter

This study investigates that the concurrent influence of El Niño-Southern Oscillation (ENSO) on the Arctic Oscillation (AO) mediated through the poleward translation of extra-tropical cyclones (ECs) over the North Atlantic is more significant than the one-year-lagged impact of ENSO through poleward propagating atmospheric angular momentum. Specific results show that during El Niño (La Niña) winter, the anomalous atmospheric horizontal heat advection from the Pacific to the Atlantic, which is caused by the southward (northward) displacement of the westerly jet stream, enhances (weakens) the atmospheric baroclinicity over the subtropical North Atlantic. Subsequently, the changed baroclinicity drives intensified (reduced) baroclinic energy conversion from the eddy available potential energy to the eddy kinetic energy, which shifts the genesis locations of ECs southward (northward) and suppresses (enhances) their poleward translation into the Arctic. Ultimately, through the combined thermodynamic and dynamical forcing associated with EC activity, the negative (positive) AO pattern is generated in the concurrent winter.