What is the Pacific decadal oscillation and how does it affect climate?
The Pacific decadal oscillation is a recurring pattern of ocean and atmosphere variability centered over the mid-latitude Pacific basin, detected as alternating bands of warm and cool surface water north of 20 degrees north latitude. During its positive phase, the western Pacific cools and parts of the eastern ocean warm, pushing temperatures above normal from the Pacific Northwest to Alaska while lowering them across Mexico and the southeastern United States. It also influences drought patterns in the United States and rainfall over the Indian subcontinent.
Who named the Pacific decadal oscillation and when?
Steven R. Hare named the Pacific decadal oscillation in 1997 while studying salmon production patterns in the North Pacific. He noticed that sea surface temperature records formed a coherent oscillating signal that corresponded with long-term shifts in salmon catches.
How far back has the Pacific decadal oscillation been reconstructed?
MacDonald and Case reconstructed the PDO index back to the year 993 using tree rings from California and Alberta. A separate reconstruction using tree-ring chronologies from the Baja California area extends the PDO signal back to 1661.
What causes the Pacific decadal oscillation?
The PDO is not driven by a single mechanism but is the sum of several processes. At inter-annual timescales it reflects El Nino-induced variability in the Aleutian Low and random atmospheric forcing; at decadal timescales, ENSO teleconnections, stochastic atmospheric forcing, and North Pacific oceanic gyre circulation each contribute roughly equally. Modeling studies suggest random atmospheric forcing alone accounts for as much as one third of PDO variability at decadal timescales.
How does the Pacific decadal oscillation affect salmon populations?
Two documented PDO polarity reversals, those occurring around 1947 and 1977, corresponded with dramatic shifts in salmon production regimes across the North Pacific Ocean. After the 1997-1998 transition back to a cool phase, substantial changes in populations of salmon, anchovy, and sardine were observed along the United States west coast.
How predictable is the Pacific decadal oscillation?
NOAA's Earth System Research Laboratory produces experimental PDO forecasts using linear inverse modeling, but predictive skill is limited to roughly four seasons ahead. Most of that skill derives from ENSO dynamics and the global temperature trend rather than extra-tropical processes, because the PDO lacks a strong intrinsic periodicity at decadal timescales.