Wednesday, September 2, 2009

Mixed El Niño indicators, but Pacific continues to warm

Bureau of Meteorology, ENSO wrap-up, 2 Sept 2009

Temperatures have risen across the equatorial Pacific during the past fortnight, in response to generally weakened Trade Winds. However, the warming has been strongest in the west of the basin which has resulted in anomalous warmth across the entire breadth of the Pacific. The typical El Niño pattern sees warmth concentrated in the central or eastern Pacific with cooler than normal temperatures in the western Pacific.
Furthermore, the coupling between the ocean and atmosphere which amplifies and maintains El Niño events has so far failed to eventuate. The neutral SOI (−5) and sub-surface cooling are evidence of this.
Leading climate models continue to predict further development of the El Niño (i.e. warming of the Pacific), although not as emphatically as a month or two back. Therefore, the odds remain strongly in favour of 2009 being recognised as an El Niño year.
El Niño events are usually (but not always) associated with below normal rainfall in the second half of the year across large parts of southern and inland eastern Australia. In keeping with this, rainfall has been below average across much of eastern Australia during July and August, with particularly dry conditions through Queensland and parts of NSW.
Conditions have recently been very warm for the time of year across Australia, with the national mean August temperature being the highest since records began in 1950. For more information about the exceptional winter heat over large parts of Australia see the Special Climate Statement issued on the 26th of August.
The most recent values of the Indian Ocean Dipole (IOD), as measured by the Dipole Mode Index (DMI), are near zero. The Bureau's POAMA model suggests the DMI should remain neutral over the coming months.

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