About Pacific Northwest Climate

Comparing ENSO and PDO

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Distinctions Between PDO and ENSO

The PDO is distinct from ENSO in three ways:

Table of PDO-ENSO Years

Table 1 categorizes past winters according to ENSO and PDO phases since 1900. The table assumes the PDO pattern is truly regime-like, with continuous epochs switching phase in 1925 (from cool to warm phase), 1947 (from warm to cool phase), and 1977 (from cool to warm). Since 1999, the PDO has shifted every few years between cool and warm phase, making it difficult to determine at this time if the 1998 shift was a true shift to a cold phase.

Years are categorized as El Niño or La Niña when temperatures in the Niño 3.4 region of the tropical Pacific average one-half standard deviation, or approximately 0.5°C, above (El Niño) or below (La Niña) mean temperature for three consecutive months. Years that do not exceed the one-half standard deviation threshold are considered ENSO Neutral. The base period used by NOAA for calculating departures from the mean is 1971-2000. For Table 1, we use the base period 1900-99.

The ENSO and PDO states assigned in Table 1 to any given year span the fall of the prior year and the winter of the listed year (e.g., "2004" refers to fall [Oct-Dec] 2003 and winter [Jan-March] 2004). The potential for precipitation and temperature extremes is higher when ENSO and PDO are in the same phase.

Table 1 ENSO/PDO phases since 1900*.
    Cool phase (negative) PDO:
1900-1924, 1947-1976, 1999-2002, 2006-May 2009
Warm phase (positive) PDO:
1925-1946, 1977-1998, 2003-2005
ENSO Phase

La Niña
(cool)

1904, 1910, 1911, 1916, 1917, 1918,
1921, 1925, 1933, 1943, 1945, 1950,
1951, 1955, 1956, 1957, 1965, 1968,
1971, 1972, 1974, 1976, 1989, 1999,
2000, 2008, 2011, 2012

1907, 1909, 1913, 1922, 1923, 1927,
1929, 1932, 1934, 1937, 1938, 1939,
1984, 1985

ENSO Neutral

1920, 1946, 1947, 1949, 1953, 1962,
1963, 1967, 1975, 1979, 1990, 2002,
2006, 2009

1901, 1902, 1908, 1928, 1930, 1935,
1936, 1944, 1948, 1960, 1961, 1981,
1982, 1986, 1994, 1996, 1997, 2001

El Niño
(warm)

1912, 1915, 1952, 1954, 1964, 1966,
1969, 1973, 1991, 1995, 2007
1900, 1903, 1905, 1906, 1914, 1919, 1924, 1926, 1931, 1940, 1941, 1942, 1958, 1970, 1977, 1978, 1980, 1983, 1987, 1988, 1992, 1993, 1998, 2003, 2004, 2005, 2010
* The methodology used to classify years according to ENSO and PDO phase was updated in June 2009, resulting in a small number of years being reclassified relative to the previous version of this table. The PDO value for 1959 is zero, and this year is not included in the table.

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Last update: 6.30.09