Classification of El Niño and La Niña Winters
A number of WRCC ENSO tables and graphs are stratified by
June-November Southern Oscillation Index (SOI), following the logic of
Redmond & Koch (1991, 2381-2399, Water Resources Research). Slightly
better relations are found between western climate and SOI than with
SST (Sea Surface Temperatures). Also, better relations are often
found when SOI leads winter climate (by about 4 months) rather than
being concurrent with climate. And, whether better, similar, or even
slightly worse, the predictive utility is retained with the earlier
SOI period. Because the SOI is averaged over 6 months, the lead and
lag periods are not completely separated (2 month overlap for Oct-Mar
climate elements), but by early winter (Sept or Oct) the "ball park"
value of the SOI is usually apparent.
Strictly speaking, with this approach ENSO phase is determined by
atmospheric quantities (SOI). "El Nino" and "La Nina" are usually
defined solely by ocean temperatures (SST). The relationship between
the two is strong enough that most moderately positive SOI years are
also "La Nina" and most moderately negative SOI years are also "El
Nino", and the terms are used interchangeably, at some risk of
misinterpretation, to denote ENSO phase.
*** Note ***
(Many El Nino, La Nina, Neither Nino categorization approaches use ocean criteria, such as Sea Surface Temperatures (SST), rather than atmospheric criteria, such as the Southern Oscillation Index (SOI). Most categorizations produce the same years; however, typically a few years are included with one approach that are not included in another, and vice versa. )
SE - Strongly Negative SOI (-1.00 or less) - "Stronger El Nino"
EN - Mildly Negative SOI (-0.50 or less) - "Moderate El Nino"
N - Neither (SOI between -0.50 and +0.50)- "Neither Nino" or "Nada Nino"
LN - Mildly Positive SOI (+0.50 or more) - "Moderate La Nina"
SL - Strongly Positive SOI (+1.00 or more) - "Stronger La Nina"
Unless stated otherwise, the term "El Nino" based on SOI usually
includes EN and SE cases.
Unless stated otherwise, the term "La Nina" based on SOI usually
includes LN and SL cases.
Jun-Nov Following Label
Year Ave SOI Winter -- -- - -- --
1933 0.13 1933-34 N
1934 -0.05 1934-35 N
1935 0.18 1935-36 N
1936 -0.42 1936-37 N
1937 -0.23 1937-38 N
1938 1.20 1938-39 SL
1939 -0.58 1939-40 EN
1940 -1.80 1940-41 SE
1941 -1.73 1941-42 SE
1942 0.28 1942-43 N
1943 0.22 1943-44 N
1944 -0.52 1944-45 EN
1945 0.45 1945-46 N
1946 -1.05 1946-47 SE
1947 0.52 1947-48 LN
1948 -0.25 1948-49 N
1949 -0.43 1949-50 N
1950 1.55 1950-51 SL
1951 -1.07 1951-52 SE
1952 0.05 1952-53 N
1953 -0.75 1953-54 EN
1954 0.18 1954-55 N
1955 1.50 1955-56 SL
1956 0.88 1956-57 LN
1957 -0.62 1957-58 EN
1958 -0.12 1958-59 N
1959 -0.18 1959-60 N
1960 0.27 1960-61 N
1961 -0.12 1961-62 N
1962 0.38 1962-63 N
1963 -0.92 1963-64 EN
1964 0.87 1964-65 LN
1965 -1.58 1965-66 SE
1966 -0.08 1966-67 N
1967 0.10 1967-68 N
1968 0.15 1968-69 N
1969 -0.67 1969-70 EN
1970 0.77 1970-71 LN
1971 0.92 1971-72 LN
1972 -1.28 1972-73 SE
1973 1.28 1973-74 SL
1974 0.55 1974-75 LN
1975 1.83 1975-76 SL
1976 -0.52 1976-77 EN
1977 -1.52 1977-78 SE
1978 0.00 1978-79 N
1979 0.05 1979-80 N
1980 -0.38 1980-81 N
1981 0.42 1981-82 N
1982 -2.42 1982-83 SE
1983 -0.12 1983-84 N
1984 -0.22 1984-85 N
1985 -0.37 1985-86 N
1986 -0.22 1986-87 N
1987 -1.35 1987-88 SE
1988 1.25 1988-89 SL
1989 0.22 1989-90 N
1990 -0.23 1990-91 N
1991 -0.95 1991-92 EN
1992 -0.80 1992-93 EN
1993 -1.08 1993-94 SE
1994 -1.43 1994-95 SE
1995 0.00 1995-96 N
1996 0.47 1996-97 N
1997 -1.67 1997-98 SE
1998 +1.05 1998-99 SL
1999 +0.40 1999-00 N (ocean temperatures definitely LN)
2000 +0.57 2000-01 LN
2001 -0.17 2001-02 N
2002 -0.83 2002-03 EN
2003 -0.33 2003-04 N
2004 -0.73 2004-05 EN (ocean temp met EN criteria, too)
2005 0.08 2005-06 N (mild La Nina developed in mid-winter)
2006 -0.90 2006-07 EN (ocean temp moderately EN, too)
Questions?
Dr. Kelly Redmond krwrcc@dri.edu
Western Regional Climate Center, wrcc@dri.edu