Parameter Tree:
EARTH SCIENCE > CLIMATE INDICATORS > ATMOSPHERIC/OCEAN INDICATORS > SEA SURFACE TEMPERATURE INDICES > CENTRAL TROPICAL PACIFIC SST

Definition:
The Niño4 SST anomaly index is an indicator of western tropical Pacific El Niño conditions. It is calculated with SSTs in the box 160°E - 150°W, 5°S - 5°N.

Reference:
Ocean Observations Panel for Climate (OOPC):
http://ioc3.unesco.org/oopc/state_of_the_ocean/sur/pac/nino4.php