On The Bimodality Of Enso Cycle Extremes

Download or read book On the Bimodality of ENSO Cycle Extremes written by Robert M. Wilson and published by . This book was released on 2000 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt: On the basis of sea surface temperature in the El Niño 3.4 region (5° N.-5° S., 120°-170° W.) during the interval of 1950-1997, Kevin Trenberth previously has identified some 16 El Niño and 10 La Niña, these 26 events representing the extremes of the quasi-periodic El Niño-Southern Oscillation (ENSO) cycle. Runs testing show that the duration, recurrence period, and sequencing of these extremes vary randomly. Hence, the decade of the 1990's especially for El Niño, is not significantly different from that of previous decadal epochs, at least, on the basis of the frequency of onsets of ENSO extremes. Additionally, the distribution of duration for both El Niño and La Niña looks strikingly bimodal, each consisting of two preferred modes, about 8- and 16-mo long for El Niño and about 9- and 18-mo long for La Niña, as does the distribution of the recurrence period for El Niño, consisting of two preferred modes about 21- and 50-mo long. Scatterplots of the recurrence period versus duration for El Niño are found to be statistically important, displaying preferential associations that link shorter (or longer) duration with shorter (longer) recurrence periods. Because the last onset of El Niño occured in 1997 and the event was of longer than average duration, onset of the next anticipated El Niño is not expected until February 2000 or later.