PDO (Pacific Decadal Oscillation)
An introduction to Pacific Decadal Oscillation Theory
Sandro Wellyanto Lubis
Lubis, Sandro Wellyanto. 2011., Stochastic Process in the Time Series Model of Pacific Decadal Oscillation (PDO). Journal of Aeorospace Science LAPAN, 9 (1), 36-52, 2011. Donwload here: 1687-1689-1-SM
Figure 1. Sea Level Pressure (contours) and surface windstress (arrows) anomaly patterns during warm and cool phases of PDO [http://jisao.washington.edu/pdo]
Pacific Decadal Oscillation (PDO) is one of the climate variability generated by coupled interaction between ocean and atmosphere, primarily occurs in the Northern hemisphere of Pacific Ocean. This phenomenon was discovered by fisheries scientist Steven Hare in the mid-1990’s, based on observations of Pacific fisheries cycles [Mantua N.J 1999]. He named it when he studied about salmon production pattern in the Northern Pacific Ocean [Mantua et al 1997]. PDO cycle is characterized by the presence of warm and cool surface waters in the Pacific Ocean and the regimes shift from warm (positive phase) to cool (negative phase) in decadal time scale [Mantua and Hare 2002]. The cool period, for instance, is actually associated with extremely high sea surface temperatures in the Northern Pacific and the warm period is reversed (figure 1).
PDO is almost similar to the El-Nino Southern Oscillation (ENSO) and some call as long-lived El-Nino-like pattern of pacific climate variability because both of these ‘event’s occur in the Pacific Ocean and highly detected in the variability of Pacific Ocean SST, but some scientists argue that based on collective body of research, there are three main characteristics distinguishing PDO from ENSO [Mantua et al 1997] : first, Period of oscillation, PDO has shifts phase on at least in inter-decadal time scale, persisted about 20 to 30 years. While ENSO is commonly known as inter-annual climate variability, persisted for 6 to 18 months in this region; second, visibility of climatic fingerprints of the PDO; and the third the mechanisms causing PDO variability were not known well, while causes for ENSO variability were relatively well-understood [Zhang et al. 1997, Mantua et al. 1997, NRC 1998].
The best way to detect a signal of PDO event is by determining the index of PDO which is defined as the leading principal component of North Pacific monthly sea surface temperature variability from an un-rotated empirical orthogonal function analysis [http://jisao.washington.edu/pdo/]. The index is measured poleward of 20 degrees north latitude and very useful to describe the climate variation attributed to the Pacific Decadal Oscillation [Mantua et al 1997, Zhang et al 1997]. The most commonly PDO index is developed by Mantua [ftp://ftp.atmos.washington.edu/mantua/], but there are other PDO indexes developed from outside North America such as PDO index introduced by Evans et al  and Linsley et al  which are interesting because they substantiate a robust PDO to tropical and southern hemisphere climate [Evan et al 2000] .
The research that was conducted by Mantua and Hare 2002, assertively explained some impacts emerging by strengthening and weakening of PDO event. The existence of PDO event affects the surface climate anomaly in some regions, for example the warm phase of PDO coincide with anomalously dry period in eastern Australia, Korea, Japan, Interior Alaska and in a zonally elongated belt from Pacific Northwest to northern South America; warm PDO phases also tend to coincide with anomalously with wet periods in southwest US, Mexico, southeast brazil, south central South America and western Australia ; the PDO ‘event’ is also broadly affected temperature from northwestern North America to Northwestern Australia [Mantua et al 2002, Willmott and Robeson 1995]. Mantua et al  also noted that PDO ‘event’ has widespread impacts on natural system, including water resources in the Americas and many marine fisheries in North Pacific. In other words, the decadal variation of these shift phases of PDO ‘event’ has influenced the large-scale spatiotemporal patterns of large-scale wildfires occurrence in Northern American and also in the other areas geographically affected by this phenomenon [Nairn-Birch 2008]. A study of PDO researched by Faqih et al  showed that PDO and IPO are linked to low-frequency of rainfall variability in the Austral- Indonesian region through regulating regional SST patterns . He indicated that there was a significant relationship between interdecadal SST anomaly and rainfall variability.