Pacific Decadal Oscillation

The “Pacific Decadal Oscillation” (PDO) is a long-lived El Niño-like pattern of Pacific climate variability.

Both PDO and ENSO have similar spatial climate fingerprints yet the major difference is that PDO persists for 20-30 years while the typical ENSO persists for 6 to 18 months.

The primary climatic fingerprints of the PDO are most visible in the North Pacific/North American sector, while secondary signatures exist in the tropics. On the contrary, the primary climatic fingerprints of the ENSO are visible in tropics while secondary are visible in North Pacific/North American sector.

The PDO has two cycles, viz. Cold Cycle and Warm Cycle, very much similar to La Nina and El Nino of the ENSO cycle.

Major changes in northeast Pacific marine ecosystems have been correlated with phase changes in the PDO; warm eras have seen enhanced coastal ocean biological productivity in Alaska and inhibited productivity off the west coast of the contiguous United States, while cold PDO eras have seen the opposite north-south pattern of marine ecosystem productivity.

Reasons

PDO is under studies. Causes for the PDO are not currently known. Potential predictability for this climate oscillation are also not known.

Influences

The PDO has a major influence on Alaskan and for those matter global temperatures. The positive phase favors more El Ninos and a stronger Aleutian low and warm water in the north Pacific off the Alaskan coast. The negative phase more La Ninas and cold eastern Gulf of Alaska waters. Note the strong similarity of the positive phase with El Nino and  the negative with La Nina.

PDO is responsible for bringing colder surface water temperatures and thus beginning the overall cooling effect in recent times in Alaska. This oscillation has brought a weakening of the ‘Aleutian Low’, the breeding ground for storms that end up regulating weather systems in the rest of the 48 states. With a less active Aleutian Low, cold winter storms have been sticking around Alaska longer and keeping the temperatures chilly.

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