What is the Pacific Decadal Oscillation?
The PDO is a long-term (10-20 year) oscillation of the Pacific Ocean in response to the changes in the atmosphere. During a warm (positive) phase, the response of the ocean to low atmospheric pressure over the Aleutian Islands causes ocean currents to bring warm waters in the Eastern Pacific Ocean and along the coast of North America and cool nutrient-rich waters in the western Pacific Ocean. This leads to higher sea levels along the coastlines of the Northeast Pacific. During a cool (negative) phase the Eastern Pacific Ocean becomes cooler and the Western Pacific Ocean becomes warmer. This leads to lower sea levels along the coastlines of the Northeast Pacific.
What are we looking at?
The plot tracks the conditions in the Pacific Ocean, showing the phase of the PDO both now and in the past. When the value of the time series is positive, the warm phase of the PDO is present with higher sea level in the Northeast Pacific. When the value is negative, the cool phase of the PDO is present with lower sea level in the Northeast Pacific. The plot tracks the conditions in the Pacific Ocean, when the value of the time series is positive (red shading), El Niño conditions are present, and when the value is negative (blue shading), La Niña conditions are present.
Why do we care?
The PDO has impacts on fisheries, especially on salmon production in Alaska which is enhanced during a warm phase. Also, the PDO has impacts on weather: a warm (cold) phase tends to cause heavy rains (droughts) in Eastern Pacific Ocean and droughts (floods) in Asia and Australia. In terms of sea-level change, the PDO is associated with sustained increases and decreases in sea level over the course of a decade or more, causing changes in coastal impacts.
Reference: Hamlington et al., 2019