DOCUMENTATION OF A HIGHLY ENSO-RELATED SST REGION IN THE EQUATORIAL PACIFIC

A new ENSO SST index is documented that is strongly correlated to the core ENSO phenomenon. The SST anomaly in much of the east-central and eastern tropical Pacific is closely related to ENSO. However the anoma ly from approximately the centre of the eastern half of the equatorial Pacific westward to near tile date line is suggested to be most stron gly ENSO-related when darn spanning the most recent several decades ar e used. This is the case both with respect to (1) strength of associat ion with other oceanic/atmospheric ENSO-related anomalies (both simult aneously and as a time-delayed predictand), and (2) impact on remote w orldwide climate anomalies. This observational insight was lacking in the early 1980s when the four ''Nino'' regions were developed. While a firmer dynamical foundation for this regional preference still needs to be established the region straddling Nino 3 and Nino 4 may be regar ded as an appropriate general SST index of the ENSO state by researche rs, diagnosticians and forecasters. A dataset of this index, called '' Nino 3.4'' (5 degrees N-5 degrees S, 120-170 degrees W), is maintained an the Internet, shown in the Climate Diagnostics Bulletin, and provi ded in the Appendix of this note.