gl'lNN KT AL SOUTHERN OSCILLATION, KL NINO, AND INDONESIAN DKOIIGHTS 



since an additional contribution was introduced in 

 the following year. The foregoing assumptions 

 were based on findings from a study of the South- 

 ern Oscillation index trends and associated events 

 over recent decades when more data were avail- 

 able for case history studies. 



Our study of strong events was limited to the 

 period 1763-present (Table 2, Figure 5), since the 

 break of 35 yr between 1728 and 1763 was 14 yr 

 longer than the longest subsequent break between 

 events, and there was no way of eliminating the 

 possibility that one or more strong events might 

 have gone unreported over the 35-yr gap. These 

 data indicate that given a strong El Niiio, there is 

 a 3d7c probability of having another strong event 

 in 7-8 yr, and an 82^7^ probability of having one 

 within the next 15-16 yr. Considering all available 

 data, the time between onsets of separate strong 

 events was never <7 yr. 



For strong and moderate events (Table 3, Fig- 

 ure 5) the record was limited to the period 

 1791-present when data for both categories were 

 available. For strong, moderate, and weak events 

 (Table 4, Figure 5) the record was limited to 

 1842-present, so we would have at least one index 

 component trend available for cross-checking the 

 less prominent weak events. (Madras pressure 

 data became available in 1841.) With the addition 

 of very weak events (Table 5, Figure 5), we limited 

 our record to 1862-present in order to have an 



50 



3 



o 



> 



Slrong Events 

 .(1763-19721 



Slrong , Moderate 

 and Weak Events 



0.50- 







3 3 



> I cvj I ^ T il ool ol *^ 



(NJ I ^ ! U3 



fo >n r^ 



Strong and Moderate 



Events 



25 - 



Strong , Moderate, Weak 

 and Very Weali Events 



CLASS LIMITS (years) 



Figure 5. — Histograms of frequency distributions for El Nino 

 type events by intensity. Number of occurrences within class 

 intervals is indicated. 



index trend available for cross-checking the more 

 obscure very weak events. (The Santiago-Bombay 

 index became available in 1861.) 



Cases were noted where relaxation from a large 

 preevent index anomaly peak appeared to be a two 

 or more stage process. [This type development was 



Table 2. — Strong El Ninos, with intervals between events from 

 onset to onset. 



1763 

 1770 

 1791 

 1804 

 1814 

 1828 

 1845 

 1864 

 1877 



209 (cumulative years between onsets) - 17 (number of intervals) = 12.3 yr, 

 average time interval between onsets of strong El Ninos. 



Table 3. — Strong and moderate El Nines with intervals be- 

 tween events from onset to onset. 



Table 4. — Strong, moderate, and weak El Ninos with intervals 

 between events from onset to onset. 



1844 



1845 



1850 



1852 



1855 



1857 



1864 



1868 



1871 



1873 



1877 



1880 



1884 



1887 



1891 



1896 



1899 



1902 



132 (cumulat 



average time 



1845 

 1850 

 1852 

 1855 

 1857 

 1864 

 1868 

 1871 

 1873 

 1877 

 1880 

 1884 

 1887 

 1891 

 1896 

 1899 

 1902 

 1905 



1 

 5 

 2 

 3 

 2 

 7 

 4 

 3 

 2 

 4 

 3 

 4 

 3 

 4 

 5 

 3 

 3 

 3 



ive years between onsets) 

 interval between onsets. 



1905 

 1911 

 1914 

 1917 

 1918 

 1923 

 1925 

 1929 

 1932 

 1939 

 1941 

 1943 

 1951 

 1953 

 1957 

 1965 

 1969 

 1972 

 36 (number 



1911 

 1914 

 1917 

 1918 

 1923 

 1925 

 1929 

 1932 

 1939 

 1941 

 1943 

 1951 

 1953 

 1957 

 1965 

 1969 

 1972 

 1976 

 of intervals) 



6 

 3 

 3 

 1 

 5 

 2 

 4 

 3 

 7 

 2 

 2 

 8 

 2 

 4 

 8 

 4 

 3 

 4 

 3.7 yr. 



673 



