Pacific Decadal Oscillation (PDO)

The Pacific Decadal Oscillation (PDO) is the leading pattern of North Pacific SST variability, an ENSO-like horseshoe defined as the first empirical orthogonal function of SST anomalies north of 20 degrees N. Its positive (warm) phase has cool central North Pacific SST ringed by warm coastal and tropical water; the negative phase reverses this. Phases persist 20 to 30 years but flip on shorter scales too, so the PDO is best read as a reddened mix of ENSO teleconnections, ocean gyre dynamics, and Aleutian Low forcing. It modulates salmon production, drought, and decadal warming rates.