The changing influences of the AMO and PDO on the decadal variation of the Santa Ana winds

Santa Anawind (SAW) events have great implications for the environment of SouthernCalifornia, but the cause of their decadal variability has not been fully understood.We showwith observational analysis that theAtlanticmulti-decadal oscillation (AMO)has a stronger influence than the Pacific decadal oscillation (PDO) inmodulating SAWactivity through twomechanisms: theGreat Basin pressure gradientmechanism, inwhich a strengthenedGreat Basin high promotes SAWactivity and vice versa through the northeast–southwest pressure gradient across SouthernCalifornia, and the Pacific jetstreamdisplacementmechanism, inwhich a strengthened Pacific subtropical high (PSH) prohibitsmid-latitude cyclones from traveling towardCalifornia, consequently encouraging SAW development and vice versa.While the AMO strengthens or weakens both theGreat Basin and PSHs to stronglymodulate SAWactivity through these twomechanisms, the PDO strengthens one of the highs but weakens the other, causing the twomechanisms to cancel each other, producing little influence on SAWactivity. A projection based on the AMOandPDO indicates that the above-average SAWactivity observed since the beginning of the 21st century is likely to terminate after 2016, after which SouthernCaliforniamay experience an extended period of below-average SAWactivity through 2030.