SOI Update (Dated 18th March)
As readers would be aware, an El Nino sea temperature pattern has been the dominant feature of the Australian climate over the last 9 to 12 months. The 2002/03 El Nino event will be remembered for it's negative impact not only on rainfall patterns but also on expected crop yields and animal production Australia wide.
This El Nino pattern can still be found in the central Pacific Ocean. Warm sea temperature anomalies of around +0.9 to +1.5Â°C can still be found in the Nino 3 and 4 regions (along the equator running eastward from the international dateline). Based on changes in both the atmosphere and Pacific Ocean there is increasing optimism that this pattern is starting to break down. While this is good news, current indications suggest that it will still linger through to mid/late autumn.
Occasionally, average to above winter rain and potential high winter crop yields occur during the winters following an El Nino event. Some years that were examples of this include 1978, 1983, 1988, and 1998 (although 1998 was actually too wet in many areas with resultant crop diseases).
While the risk is low, there also remains a chance that the El Nino will regenerate in some form during autumn/winter this year. Autumn 1992 is a good example of a partial breakdown in an El Nino pattern with it then reforming in early winter (not necessarily as a classic El Nino but something close to it). Some relief rain followed by a fairly dry winter usually characterizes this type of pattern. These types of years are comparatively rare but include 1992, 1993, 1994, 1940, 1941, 1912, 1913, 1914, and 1915.
The main area of concern at present is some recently recorded minor westerly wind bursts in the central Pacific. As regular readers of this column would be aware, westerly wind bursts in the central Pacific at this time of year can be an early warning as to a developing (or re-occurring) El Nino event.
For those interested, ocean and coupled ocean/atmosphere forecast models (GCM's) give an indication as to likely ENSO development out to 9 months. Of the 10 models that forecast out to July 2003, 7 indicate the development of neutral sea temperature patterns, 2 indicate ongoing El Nino (or warm) sea temperature pattern and 1 indicates the potential development of a La Nina (or cold) sea temperature pattern.
Of the 7 models that forecast out to October 2003, 6 indicate the development of a neutral sea temperature pattern while 1 indicates the development of a La Nina sea temperature pattern.
GCM outputs should be viewed cautiously at this time of year as we are approaching the so-called "predictability barrier" between March and June. More details can be found at www.bom.gov.au/climate/ahead/ENSO-summary.shtml
For the latest and most up to date information on the seasonal outlook for your location try the "Climate Note" at www.dpi.qld.gov.au/climate, Australian Rainman or contact the DPI Call Centre on 13 25 23.