The Niño indices have turned. Nino3.4 and the Southern Oscillation Index (SOI) have been in the El Niño phase for almost 2 years but they have both just moved weakly into the La Niña phase and everyone is waiting to see what the future holds.
During La Niña the trade winds are stronger than usual, allowing a warm pool of water to pile up north of New Guinea, and altimeter data is showing us that the sea level is starting to rise (right). Sea level anomalies north of New Guinea (SLA-NNG) are strongly negatively correlated with Nino3.4 and both indices have recently jumped sharply.
Warm water is more easily evaporated, providing more moisture to weather systems passing over it. With La Niña’s stronger trade winds this moisture is directed over eastern and northern Australia particularly during winter and spring. For Australia, the La Niña event of 2010-2011 was one of the strongest on record, bringing devastating floods to southeast Queensland and Victoria.
The high western Pacific sea level anomaly associated with La Niña has consequences for the west coast of Australia: inducing a strong Leeuwin Current and warmer ocean temperatures. In early 2011, the west coast experienced an unprecedented marine heat wave (Ningaloo Niño) largely due to the strengthening of the Leeuwin Current during the summertime, when it is usually at it’s weakest, assisted by an anomalous heat flux into the ocean. This warming event caused drastic changes in the marine ecosystem and strongly impacted fisheries off the west coast. The Niño indices can give us some indication of what is to come for the summer of 2017 but leading CSIRO scientist, Ming Feng, warns that the contribution of local air-sea coupling remains unpredictable.
This news item was published on the IMOS OceanCurrent website and written by Madeleine Cahill.