Both time series have been smoothed with successive 11- and 9-point running means. Anomalies with respect to 1877-1996.
The following is an SOI calculated from sea-level pressure (SLP) measurements contained in the Comprehensive Ocean-Atmosphere Data Set (COADS).
The "Tahiti" pole of the SOI is calculated as the area-average SLP anomaly for 20N-20S, 180-70W. The "Darwin" pole is the area-average SLP anomaly for the rest of the tropical band equatorward of 20 degrees of latitude (20N-20S, 70-0W and 20N-20S, 0-180E). The SOI is calculated as the difference "Tahiti" minus "Darwin", and is in units of mb. Anomalies are given with respect to the period 1900-79. Additional details of the index calculation are given at the bottom of this page.
Both time series have been smoothed with successive 11- and 9-point running means. Anomalies with respect to 1877-1996.
Click here to obtain the timeseries in MATLAB format. [The variable name within MATLAB will be "soi".]
In the following table, the SOI values are in units of hundredths of millibars, and missing values are indicated by blanks.
Additional details Climatological SLP maps are calculated for the years 1900-79, and the resultant maps smoothed along latitude circles with successive 5- and 3-point running means. The climatology maps are subtracted from the raw data to produce SLP anomaly maps. Time series for the "Tahiti" and "Darwin" poles are then calculated, with the contribution of each 2-degree latitude-longitude grid box anomaly weighted by the number of observations contributing to that anomaly measurement. Anomalies are then calculated for the "Tahiti" and "Darwin" time series with respect to the period 1900-79. "Tahiti" and "Darwin" anomalies in excess of 3 mb in magnitude are set to missing, and the anomalies recalculated. The "Tahiti" ("Darwin") time series had 4 (0) values in the period 1900-79 set to missing in this procedure. The SOI is then calculated as the difference of "Tahiti" minus "Darwin". SOI anomalies are recalculated with respect to 1900-1979 (the months of missing data for the "Tahiti" and "Darwin" are not all the same).jan feb mar apr may jun jul aug sep oct nov dec 1877 -119 107 -120 75 -76 -41 -71 -101 1878 -297 -387 -122 311 156 -80 84 27 141 1879 166 141 72 146 106 -131 30 -108 -76 156 139 361 1880 -148 -24 104 -90 50 -33 -60 59 -10 -9 1881 -142 146 51 107 -88 178 147 120 9 105 96 120 1882 -52 106 -6 234 221 -177 -116 82 145 -47 135 -34 1883 124 -83 43 60 115 -75 -65 -117 -68 89 -34 -181 1884 21 136 26 -95 -72 29 -43 45 -52 -128 -188 -97 1885 -68 51 -86 -76 -70 18 142 9 28 25 -17 100 1886 69 -2 120 157 63 161 103 228 176 256 45 224 1887 255 38 48 65 98 -6 -11 156 100 39 243 39 1888 36 -31 -111 -120 -20 -125 -145 -84 -105 32 -115 -176 1889 -167 -137 -26 53 -102 117 138 194 208 262 228 172 1890 236 75 140 210 66 108 65 90 -16 84 -49 137 1891 -43 -169 52 79 -24 -105 -72 -62 -18 99 52 240 1892 -75 76 169 219 -58 -16 -58 294 142 150 -62 242 1893 -1 27 116 193 53 -1 229 155 354 152 237 236 1894 65 138 31 -118 -57 68 133 -118 -80 -23 22 6 1895 -37 -62 120 -49 -170 1 152 42 101 197 114 1896 141 -91 12 117 53 -118 -127 -51 51 28 115 -140 1897 22 -126 140 16 15 54 136 75 16 12 -15 -22 1898 61 174 82 5 11 2 24 23 -5 -14 -79 51 1899 -11 256 -154 14 -45 56 -34 -124 -155 -87 -16 -57 1900 -35 -103 -216 -138 -148 -112 61 -14 -52 -44 63 -53 1901 -118 -21 25 -2 -16 107 140 109 107 93 79 -58 1902 93 -37 53 -15 -71 -121 -59 -124 -94 -181 -195 -71 1903 -92 -231 19 54 1 -37 -26 -26 83 41 12 161 1904 68 15 10 -19 15 -108 -83 -48 -52 9 -106 -13 1905 -18 -117 -128 -120 -124 -164 -73 -99 -145 -97 -100 -68 1906 -52 76 -18 -84 -40 36 89 -98 -11 93 -32 133 1907 100 111 11 82 29 7 -43 -144 0 -1 3 -8 1908 -35 23 -2 23 -18 -60 52 7 -85 113 50 145 1909 60 144 -19 118 107 16 5 30 22 102 153 107 1910 21 100 133 41 23 76 167 133 59 24 -75 67 1911 62 -70 15 -86 -55 -94 -96 -74 34 -200 -159 -240 1912 -258 -192 -115 -94 -68 -59 -99 -43 -51 -35 -57 -30 1913 -91 0 4 -35 -30 -135 110 -7 -27 -163 -58 -73 1914 -140 -138 83 -25 28 1915 7 1916 30 1917 207 -82 170 21 93 -30 1918 -129 -149 -62 -306 -111 167 1919 112 -62 3 1920 -26 -210 64 -222 -119 -21 -91 47 143 64 35 -50 1921 49 48 77 15 145 124 49 105 120 74 -46 36 1922 9 49 90 -20 18 114 24 36 58 77 63 104 1923 40 79 35 66 -38 -65 -24 13 -24 -24 -30 -3 1924 -62 120 100 112 103 168 96 59 54 1 117 67 1925 111 27 87 50 34 -87 -25 -46 28 -88 -9 -137 1926 -66 -23 -44 -73 -13 -39 -6 -36 34 -42 41 114 1927 66 81 85 78 -36 62 -2 2 53 -2 -22 -52 1928 98 22 49 65 -33 23 -82 57 24 -47 56 39 1929 -39 32 23 6 7 11 -79 -45 -43 -90 -78 -32 1930 -44 -6 -67 -36 -108 -86 -102 -95 -165 -65 -98 -156 1931 -88 -85 -97 -86 -6 -18 -26 -66 42 -23 3 -35 1932 -59 -77 -53 -150 -67 -99 -72 -16 3 31 14 10 1933 31 101 29 -19 11 45 25 33 72 61 153 169 1934 159 171 110 55 14 -12 11 -6 3 22 -34 -35 1935 -27 134 39 19 23 22 46 4 50 -27 -34 -38 1936 -105 8 -80 17 -12 -51 -56 -96 40 8 -89 -11 1937 -100 33 -10 -12 -24 94 89 27 29 -55 14 -23 1938 -34 79 129 57 22 29 53 36 42 45 -22 52 1939 -46 20 100 -11 -61 -32 -66 55 -9 -38 7 -164 1940 -73 -142 -12 -45 44 -72 -9 8 -129 -67 -34 -197 1941 -40 -101 -169 -90 -145 28 -137 -3 -130 -133 -116 -138 1942 -29 -17 17 70 67 74 56 54 28 31 37 153 1943 -8 -12 -45 -86 0 -29 -69 13 -21 45 1 38 1944 22 -68 -72 23 13 47 -12 -31 46 32 70 42 1945 164 51 110 52 31 0 23 54 -47 -81 -21 32 1946 127 -2 51 -21 -30 36 -4 17 -79 -50 38 -51 1947 -16 50 -74 84 36 -12 43 60 175 31 78 20 1948 -40 -62 -108 37 -40 5 13 14 -21 43 -95 54 1949 65 80 -16 -7 47 63 70 38 57 74 75 67 1950 152 100 83 112 77 108 105 50 4 24 104 -38 1951 144 72 38 -12 -44 -33 -67 -66 -50 11 10 20 1952 -2 28 11 -6 18 -5 31 26 -5 28 35 -34 1953 50 -56 -15 -60 -84 23 -5 -49 -23 46 -6 -3 1954 74 82 -47 45 -6 42 20 77 29 41 65 92 1955 20 88 66 58 104 86 17 47 87 100 90 105 1956 114 53 38 43 101 34 36 52 55 82 54 14 1957 58 -131 -45 -40 -70 -75 -88 -49 -64 -20 -107 -51 1958 -133 -63 -198 -79 -105 -60 -67 -33 -40 -36 -66 -60 1959 -66 -70 -36 -23 57 -15 -11 38 50 -32 68 -33 1960 51 0 63 17 19 1 6 48 18 5 38 75 1961 -46 39 -96 14 38 10 49 40 51 -26 30 67 1962 128 -7 15 62 96 5 62 -26 12 42 54 25 1963 56 55 -26 28 43 -35 -19 -31 -56 -76 -7 -55 1964 -46 -66 -35 76 62 71 10 78 33 69 15 56 1965 -12 -29 -56 44 -36 -100 -100 -98 -79 -59 -109 -95 1966 -234 -96 -13 47 23 -24 -18 16 -7 -8 89 122 1967 19 70 80 58 79 59 74 56 41 -20 19 -74 1968 4 -24 132 51 21 61 43 60 19 -32 22 -6 1969 -64 -86 -40 -38 -37 -62 -56 -135 -28 -40 -37 -35 1970 -8 3 25 -21 66 33 4 24 72 80 148 26 1971 36 126 38 98 78 93 6 12 41 27 16 -19 1972 -31 53 -44 -55 -75 -44 -25 -86 -101 -90 -80 -85 1973 -125 -53 -68 15 32 64 60 70 60 114 93 158 1974 116 126 104 39 42 33 72 27 50 104 26 13 1975 -30 55 -4 61 75 74 114 127 106 134 65 157 1976 62 126 25 -16 -24 -70 -95 -61 -70 -26 -20 -110 1977 -39 -39 -177 16 -44 6 19 -18 -11 -49 -71 -128 1978 -26 -169 -15 -26 10 50 -20 -14 -27 -15 -101 -58 1979 -31 1 -5 -51 -59 -5 -70 -35 -87 -51 -9 -63 1980 -77 -46 -229 -121 -118 -101 -82 -65 -27 -36 6 8 1981 -8 -100 -45 -25 -3 -29 14 -18 23 9 42 -89 1982 -6 -46 -78 -59 -124 -143 -94 -111 -104 -90 -168 -179 1983 -316 -265 -226 -155 -170 -143 -124 -22 -15 6 -74 -4 1984 87 19 -3 45 47 48 1 60 -17 25 57 -35 1985 107 105 -27 67 21 -54 -31 37 7 -69 -30 30 1986 -2 -9 2 -34 -57 7 -58 -52 -86 -14 -129 -131 1987 -142 -281 -127 -128 -149 -72 -169 -111 -32 -56 -41 -138 1988 19 -26 57 25 29 54 74 13 102 96 45 85 1989 126 67 110 25 68 46 58 14 -8 35 -35 -10 1990 -118 20 -66 4 28 -38 5 16 -35 -7 -66 -30 1991 10 -75 -36 -14 -51 -26 -24 -12 -92 -71 -132 -111 1992 -195 -161 -170 -139 -134 -123 -129 -25 -77 -61 -119 -151