ENSO and IOD Indices
El Niño–Southern Oscillation indices El Niño and La Niña events (referred as El Niño–Southern Oscillation or ENSO) are driven by changes in the Sea surface temperature and atmosphere in the equatorial Pacific Ocean. During El Niño, sea surface temperatures in the central and eastern Pacific Ocean become warmer than average, while La Niña is characterised by cooler than average sea surface temperatures in the same regions. To monitor the signs of El Niño or La Niña, several sea surface temperature (SST) indices are being used. These indices simply refer to the difference in sea surface temperature from the long-term mean (here 1991–2020) in several regions located along the equatorial Pacific. These regions are called NINO1 and NINO2, NINO3, and NINO3.4 and NINO4. The Niño regions cover the following areas: Nino1+2: 10°S-0, 90°W-80°W (-10 to 0, 270 to 280) Nino3 : 5°S-5°N, 150°W-90°W ( -5 to 5, 210 to 270) Nino3.4 : 5°N-5°S, 170°W-120°W ( -5 to 5, 190 to 240) Nino4