El Niño persists Dave McRae, Qld Climate Change Centre of Excellence, 27/10/09.
According to the latest ENSO Wrap-up from the Bureau of Meteorology www.bom.gov.au/climate/enso an El Niño sea surface temperature (SST) pattern continues to persist in the Pacific. Rainfall patterns over eastern Australia for the past three months have broadly been in keeping with the impact of an El Niño event.
SOI values now also appear to be reflecting the El Niño SST pattern. The 30 day average of the SOI as of the 26th October is minus 13.2. The recent and sudden fall in value of the SOI has been driven by large negative daily SOI values since early October.
It will be interesting to see if this is a longer term trend or just a short term fluctuation as we approach our summer rainfall season. Negative SOI values (say below minus 5) are normally associated with El Niño events. Typically during an El Niño event, there is a lower chance of getting above median rainfall during winter, spring and early summer throughout southern and inland eastern Australia. Therefore there will be much interest in which direction SOI values take as the summer rainfall season approaches.
Interestingly six of the seven leading international climate models surveyed indicate an El Nino climate pattern is likely to persist for the remainder of 2009. None of the surveyed climate models are forecasting any potential return of La Niña like conditions. Given that El Niño events (and La Niña's) tend to persist from autumn to autumn, this is not a surprise.
For those looking for a potential rainfall trigger the next MJO event is next expected to cross northern Australia during early to mid November.
The MJO is a band of low air pressure which originates off the east coast of central Africa. It travels eastward across the Indian Ocean and northern Australia roughly every 30 to 60 days. Because of the timing of the MJO the phenomenon is also known as the forty day wave. It can be used as an indicator for the timing of potential rainfall events.
The impact of the MJO on rainfall varies between the different seasons and location. For example the MJO has a greater influence on rainfall throughout northern Australia during summer and southern Australia during winter. For more information on the MJO go to www.bom.gov.au
You can receive a text message with the latest SOI values sent to your mobile phone. To subscribe to this free service, call me on (07) 4688 1459 or e-mail firstname.lastname@example.org The latest rainfall probability maps are available at www.longpaddock.qld.gov.au