ENSO Consensus Explained

1997ElNino

There are many ways El Nino/La Nina metrics as they range from Oceanic Nino Index (ONI), Multivariate ENSO Index (MEI), Southern Oscillation Index (SOI), and Japanese Meterological Agency ENSO Data.

I created my own El Nino/La Nina index. It is based ERSST v4 Anomaly of Region 1+2, 3, 3.4, and 4, Japanese Meterological Agency ENSO Data, SOI, and MEI. I use a weighted average system. Here is the formula I used.

(ERSST v4 Region 1+2 Anomaly*15)+(ERSST v4 Region 3 Anomaly*5)+(ERSST v4 Region 3.4 Anomaly*25)+(ERSST v4 Region 4 Anomaly*5)+(JMA ENSO*20)+(-(SOI)*20)+(MEI*25))/(15+5+25+5+20+20+25)

Here is a monthly table of ENSO Consensus. It starts at 1870. For El Nino and La Nina to be considered, it has to be consecutive for at least seven months.

ENSO Consensus
Strong La Nina = 12.25

ENSO Consensus
Strong La Nina <= -12.25
Moderate La nina -7.25 to -12.24
Weak La Nina -2.25 to -7.24
Neutral -2.24 to 2.24
Weak El Nino 2.25 to 7.24
Mild El Nino 7.25 to 12.24
Strong El Nino >= 12.25

Wonder what years had strong El Nino and La Nina? It is based on highest for El Nino or lowest for La Nina.

Strong El Nino (Based On Monthly Average >= 12.25)
1877-1878
1888-1889
1896-1897
1899-1900
1902-1903
1904-1905
1930-1931
1940-1941
1957-1958
1965-1966
1972-1973
1982-1983
1986-1987
1991-1992
1992-1993 (Burst of El Nino in most of 1993)
1997-1998
2014-2016

Strong La Nina (Based On Monthly Average <= -12.25)
1873-1874
1875-1876
1886-1887
1889-1890
1892-1893
1893-1894
1903-1904
1907-1911
1915-1918
1920-1921
1924-1925
1938-1939
1942-1943
1949-1950
1954-1957
1964-1965
1970-1971
1973-1976
1988-2001
2007-2008
2010-2011

What Years Went From La Nina To El Nino
1876
1899
1902
1904
1911
1918
1925
1930
1939
1951
1957
1963
1965
1968
1972
1976
1986
1997
2006
2009

What Years Went From El Nino To La Nina
1878
1889
1897
1903
1906
1912
1915
1926
1942
1966
1973
1983
1988
1995
1998
2007
2010
2016

Interesting to note in the years with Strong El Nino, it went to La Nina, especially since 1950. It also applies with Moderate El Nino like in 2010. I wonder why that happens. There are also more strong La Nina than El Nino. Strong La Nina usually occur when the Pacific Decadal Oscillation (PDO) is in a cool phase. There are data suggesting that cool PDO can last over 30 years and in some cases for more than 300 years during from 993 to 1300. There is also evidence of prolonged warm PDO from 1450s to 1620s, which is over 170 years. This is based on tree ring data and not directly measured like we do today. Strong La Nina have happened in warm PDO in 1988-1989 or strong El Nino in cool PDO in 1972-1973.

Warm PDO
1924-1947
1976-1998
2002-2007

Cool PDO
1890-1924
1947-1976
1998-2002
2008-?

Keep in mind, any data before 1950 should be suspect as sea surface temperature is calculated, not directly measured. If we start with 1950, here are the strong El Nino and La Nina.

Strong El Nino Since 1950 (Based On Monthly Average >= 12.5)
1957-1958
1965-1966
1972-1973
1982-1983
1986-1987
1991-1992
1992-1993
1997-1998

Strong La Nina Since 1950 (Based On Monthly Average <= -12.5)
1949-1950
1954-1957
1964-1965
1970-1971
1973-1976
1988-2001
2007-2008
2010-2011

There have been more strong La Nina than El Nino since 1950. Again this reflects that since 1950 we have mostly been in a cool PDO phase, which has account 36 years, while warm PDO have accounted 27 years.

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