ENSO Rainfall Composite

ENSO composite rainfall results for Hawaii and US-affiliated islands. The dotted line shows the climatological mean rainfall for all years, the solid line the mean for the composited 17 warm ENSO episode years, and the dashed line that for the 15 cold episode years. Vertical lines denote calendar year changes. Each plot shows composites for the period beginning about 5 seasons before the boreal winter of a mature episode and ending about 5 seasons after that winter. The notation for relative year identity (0 and +1) in is as defined in Ropelewski and Halpert (1987). Results for small portions of year -1 (late boreal autumn) and year +2 (early boreal spring) are also shown. Thus, the mature episode winter (year 0 to +1) is located near the midpoint of the abscissa range. The differences between the composited rainfall totals for the samples representing the warm or cold phases of ENSO versus the totals of the remaining years (neutral-plus-oppositely phased years) were statistically tested with the Student's t-test. It should be noted that the statistical assumptions underlying the t-test (e.g. Gaussian distributions) may not be sufficiently satisfied. Nonetheless, we use it as a rough guide for indicating significant mean differences in rainfalls as a function of ENSO category. For a given station, those seasons whose warm or cold episode years' mean passed a 2-sided test with a significance level of 0.05 or better are indicated with a hollow or solid square, respectively, along the solid or dashed curve.