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20.07.2015 01:21 Age: 2 yrs
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Sea level in the western equatorial Pacific drops dramatically

There is further evidence that 2015 is shaping up to be an El Niño year. Low sea levels observed in the western equatorial Pacific could indicate a very strong El Niño event this year.


Monthly Mean Sea Level Anomaly June 2015 (image: IMOS OceanCurrent)

Mean Sea Level Anomaly (SLA) for the Western and equatorial Pacific (image: CSIRO)

The month-average of sea level north of New Guinea has dropped to levels not seen since the ‘super El Niño’ of 1997/1998. An El Niño event occurs when sea surface temperatures in the central and eastern Pacific become sufficiently warm that the atmospheric circulation shifts resulting in weaker equatorial trade winds. Low sea levels north of New Guinea (a result of weak equatorial trade winds) are strongly correlated with Nino3.4, the El Niño index that relates best to Australian climate.

The Bureau of Meteorology declared 2015 an El Niño year in mid-May. Sea levels north of New Guinea have continued to drop sharply since then. The map at right shows the June 2015 SLA for the Australasian region, while the time-series below shows that the average for the region north of New Guinea (shown as a boxed area on the map to the right) has only been lower once before since 1992 when satellite sea level observations commenced.

Low sea levels in the western equatorial Pacific are also strongly correlated with the strength of the Leeuwin Current. There is a two month delay between the sea level anomaly off Perth and the region north of New Guinea. The low sea level signal propagates southward along the west coast of Australia weakening the Leeuwin Current and causing water temperatures to be cooler.