1. OLR Perspective on ENSO: An event-like warm-phase index A.M. Chiodi and D.E. Harrison

2. Eastern central Pacific outgoing longwave radiation (OLR) averaging region.

3. Monthly-averaged OLR Convective Index (CI, 230-OLR) over the E. Central Pacific. Periods above -15 Wm -2 are shaded red. Dashed lines at +/- 1 standard deviation, relative to mean (straight solid line.) The convective regime is shaded blue. Data from NOAA daily “Interpolated OLR.”

4. Commonly referred to monthly average ENSO indices. Base period 1971-2000. Data from HadISST and Australian Bureau of Meteorology.

5. Distributions of the monthly-averaged OLR and Nino 3.4 indices shown previously. Hash marks indicate the p=0.05, p=0.95 and most likely value for a Gaussian distributed variable with mean and standard deviation equivalent to observations.

6. OLR-basedSSTA-based (Nino3.4 Nov 1982Jul 1982 Mar 1987Nov 1986 Jan 1992Jul 1991 Jun 1997 * Jul 1997 Four events stand out during the post-1979 era. - easily identifiable - statistical and phenomenological significance Shift in convection drives the global weather anomalies. OLR warm-ENSO definition suitable for operational use. Warm event onset dates. Onset: monthly Nino 3.4 above 0.5C for 3 months for SST, monthly OLR-CI above -15Wm -2 for OLR. *first of two threshold-crossings of the 1997/1998 event.