Pacific decadal oscillation

Context: Northeast India, one of the wettest places on the Earth has been experiencing rapid drying, especially in the last 30 years. The decreasing monsoon rainfall is associated with natural changes in the Pacific decadal oscillation (PDO).

What is PDO?

The “Pacific Decadal Oscillation” (PDO) is a long-lived El Niño-like pattern of Pacific climate variability. The PDO is detected as warm or cool surface waters in the Pacific Ocean, north of 20°N.

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.

How is it different from ENSO?

Duration: 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.

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.

Sources: the hindu.