When Looking At El Nino Events, Start Time Is The Most Important Key To Determining It's Strength & Duration. Also, What Was Behind The Irregular 1986-1988 (3 year) El Nino Event?... Why Was This The Only Nino Event To Last Into 3 Years?
Created: 3-10-2008
Explanation:
How is a El Nino defined in scientific terms?
El Nino events are operationally defined using the Oceanic Niņo Index (ONI, Click Here to See ONI Index), which is the three-month running-mean values of sea surface temperature departures from average in the Niņo 3.4 region of the central Pacific (bounded by 5N-5S, 120-170W). NOAA defines El Nino as the condition whereby the ONI is more than or equal to 0.5 degrees C. This definition was adopted by the U.S. and 25 other countries in North and Central America and the Caribbean in April 2005. Source: NOAA
The Statistics of the Oceanic Nino Index show that when a El Nino Starts Early in the Year or a Late forming El Nino has a Persistence of Strength going into the 1st 3 trimonthly periods of it's 2nd Year it goes through, it will persist for longer & have greater strength. I'll explain the "Persistance of Strength" rule Later. As shown in the graphs below.
"Nino Event" are the years in which the El Nino Event occured.
"Part of Year" is the part of the year which the El Nino started. "Part of Year" can be defined by either "1st" or "2nd".
"1st" is defined as the trimonthly period of ONI from (DJF to MJJ) or the 1st part of the Year in which the El Nino Event Started, The 1st 6 months of the Year.
"2nd" is defined as the trimonthly period of ONI from (JJA to NDJ) or the 2nd part of the Year in which the El Nino Event Started, The 2nd 6 months of the Year.
"Peak C" is defined as the Highest Temperature(C) Anomaly Reading in any given trimonthly period within the El Nino. Example, the 1997-1998 El Nino Had The Warmest Trimonthly Reading Of All Time, +2.5 Degrees Celcius above average.
"Peak Rank" is nothing more then each El Nino Event Ranked by it's strength, or highest temp anomaly reading. Example, The El Nino Events of 1951-1952 & 1969-1970 only had a peak of +0.7C, which makes them the weakest El Nino's since 1949 and Ranked last in 13th place.
"Start Period" is the trimonthly period in which the El Nino Event Started, for example MAM 57 translates to March-April-May 1957.
"Start P #" is the Start Period Number, All periods from (DJF to NDJ) Are given numbers in order from (1 to 12). This helped me classify "2nd" and "1st" "Start" designations. All "1st's" are 1 to 6, and all "2nd's" are 7 to 12.
"End Period" Is the last trimonthly period the El Nino Existed.
"End P #" is the End Period Number.(1 to 12), used just like "Start P #"
"Duration" is designated as the total number of trimonthly periods in which the El Nino event Existed.
"Dur. Rank" is a Ranking of Duration, meaning El Nino's of 1951-1952 & 1969-1970 only lasted 5 trimonthly periods, they were the shortest existing classified El Nino events on Record. While The 1986-1988 Event Lasted 18 Trimonthly periods or just about 20 months, #1 in Duration Rank.
Examination:
Just like the El Nino Event's opposite, La Nina, An El Nino that starts early in the year also, AKA those designated as "1st"s have something in common. These events all have the Highest ONI Values and last for the longest durations.
Now take a look at all the El Nino events that start out in the "2nd" half of the year, one can characterize these Nino Events as shortest lasting and weaker.
Allthough there is one that defies that rule, and there is an easy explanation as of why.... The El Nino Event of 1986 into 1988. This 86/87/88 El nino Event Starts in the 2nd half of the year, one would assume it ends quickly, lasting no more then 9 trimonthly periods, but no it lasted 18 trimonthly periods through 3 different years. What did it have that the other late starting El Nino Events didn't have? Momentum heading into the next year. This is determined using the Persistence of Strength Test.
The Persistence Of Strength Match is As Follows:
The Irregular Case of El Nino 1986-1988 :
Using This Persistence of Strength Test, one can see that the beginning of 1987 featured ONI values all above 1.0 or higher. Without a drop from the DJF to FMA, That's What C represents.... The likely hood of this El Nino event to wain in Middle Year 1987 was greatly depreciated because of the momentum it had going into the Early Part of the year.
The Next Case Closest to this outcome would be the El Nino of 1968-1969, all Early year 1969 ONI values were near 1.0 but FMA was 0.9, which shows that it wasn't as persistent and fell from DJF to FMA, It had an outside shot at being within 3 years, but barely failed, The Nino Events of 68-69 and 69-70 could have easily flushed into one 68/69/70 event, but the early year momentum was not enough. Notice JJA & JAS 1969 didn't meet Nino Definition Criteria.
