| definition |
- Fisheries scientist Steven Hare coined the term "Pacific Decadal Oscillation" (PDO) in 1996 while researching connections between Alaska salmon production cycles and Pacific climate. PDO has since been described as a long-lived El Nino-like pattern of Pacific climate variability because the two climate oscillations have similar spatial climate fingerprints, but very different temporal behavior.
Two main characteristics distinguish PDO from El Nino/ Southern Oscillation (ENSO): first, 20th century PDO "events" persisted for
20-to-30 years, while typical ENSO events persisted for 6 to 18
months; second, the climatic fingerprints of the PDO are most visible in the North Pacific/North American sector, while secondary signatures exist in the tropics - the opposite is true for ENSO.
Several independent studies find evidence for just two full PDO cycles in the past century: "cool" PDO regimes prevailed from 1890-1924 and again from 1947-1976 while"warm" PDO regimes dominated from 1925-1946
and from 1977 through (at least) the mid-1990's. Shoshiro Minobe; has shown that 20th century PDO fluctuations were most energetic in two general periodicities, one from 15-to-25 years, and the other from
50-to-70 years.
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| Abstract from DBPedia | The Pacific decadal oscillation (PDO) is a robust, recurring pattern of ocean-atmosphere climate variability centered over the mid-latitude Pacific basin. The PDO is detected as warm or cool surface waters in the Pacific Ocean, north of 20°N. Over the past century, the amplitude of this climate pattern has varied irregularly at interannual-to-interdecadal time scales (meaning time periods of a few years to as much as time periods of multiple decades). There is evidence of reversals in the prevailing polarity (meaning changes in cool surface waters versus warm surface waters within the region) of the oscillation occurring around 1925, 1947, and 1977; the last two reversals corresponded with dramatic shifts in salmon production regimes in the North Pacific Ocean. This climate pattern also affects coastal sea and continental surface air temperatures from Alaska to California. During a "warm", or "positive", phase, the west Pacific becomes cooler and part of the eastern ocean warms; during a "cool", or "negative", phase, the opposite pattern occurs. The Pacific decadal oscillation was named by Steven R. Hare, who noticed it while studying salmon production pattern results in 1997. The Pacific decadal oscillation index is the leading empirical orthogonal function (EOF) of monthly sea surface temperature anomalies (SST-A) over the North Pacific (poleward of 20°N) after the global average sea surface temperature has been removed. This PDO index is the standardized principal component time series. A PDO 'signal' has been reconstructed as far back as 1661 through tree-ring chronologies in the Baja California area.太平洋十年規模振動（たいへいようじゅうねんきぼしんどう、Pacific Decadal Oscillation：PDO）とは太平洋各地で海水温や気圧の平均的状態が、10年を単位とした2単位（約20年）周期で変動する現象である。太平洋10年周期振動とも言う。海洋と大気が連動して変化する。 数十年に渡る気圧や海水温のデータから平均値を求めると、太平洋では約10年単位でその値が大きく上下に揺れる。この現象を発見したのは、サケの生息数変化を研究していたSteven R. Hareである。これとほぼ同時期にYuan Zhangは、この現象と気候との連動性を発見した。両グループは1997年に、この現象に関する論文を初めて発表した。 そのメカニズムは、まだ詳しく解明されていない。複数の説があるが、仮説の域を出ていないとされる。 (Source: http://dbpedia.org/resource/Pacific_decadal_oscillation) |
