I know El Nino ****s it right up. La Nina is the opposite weather pattern (but pretty sure not "normal" / average pattern). In the middle is the best season I think, but a La Nina doesn't make it much worse than average to good seasons, whereas a El Nino makes it a lot worse.
Howzat? Clear as mud, if you don't get it then don't worry cos I'll probably be WRONG anyway. Email BOM, they're pretty good with tech advice (unless you criticise their ability to forecast wind as effectively as they manage to forecast temps. D!c&heads.).
looks like it affect the Eastern seaboard rather than us
La Niña translates from Spanish as "the girl-child". The term "La Niña" has recently become the conventional meteorological label for the opposite of the better known El Niño.
The term La Niña refers to the extensive cooling of the central and eastern Pacific Ocean. In Australia (particularly eastern Australia), La Niña events are associated with increased probability of wetter conditions.
Changes to the atmosphere and ocean circulation during La Niña events include:
* Cooler than normal ocean temperatures across the central and eastern tropical Pacific Ocean. * Increased convection or cloudiness over tropical Australia, Papua New-Guinea, and Indonesia. * Stronger than normal (easterly) trade winds across the Pacific Ocean (but not necessarily in the Australian region). * High (positive) values of the SOI (Southern Oscillation Index).
A La Niña event is sometimes called an anti-ENSO (anti-El Niño-Southern Oscillation) event.
The Southern Oscillation Index (SOI) is calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin.
Sustained negative values of the SOI often indicate El Niño episodes. These negative values are usually accompanied by sustained warming of the central and eastern tropical Pacific Ocean, a decrease in the strength of the Pacific Trade Winds, and a reduction in rainfall over eastern and northern Australia. The most recent strong El Niño was in 1997/98.
Positive values of the SOI are associated with stronger Pacific trade winds and warmer sea temperatures to the north of Australia, popularly known as a La Niña episode. Waters in the central and eastern tropical Pacific Ocean become cooler during this time. Together these give an increased probability that eastern and northern Australia will be wetter than normal. The most recent strong La Niña was in 1988/89; a moderate La Niña event occurred in 1998/99, which weakened back to neutral conditions before reforming for a shorter period in 1999/2000. This last event finished in Autumn 2000.
For further information, have a look at the Climate Variability and El Niño brochure. Click here to find out more about El Niño and associated topics.
For the mathematically minded:
There are a few different methods of how to calculate the SOI. The method used by the Australian Bureau of Meteorology is the Troup SOI which is the standardised anomaly of the Mean Sea Level Pressure difference between Tahiti and Darwin. It is calculated as follows:
""""""""""""[ Pdiff - Pdiffav ] SOI = 10 ------------------- """""""""""""SD(Pdiff)
(Sorry Had to use " to get the formulea looking right)
where
Pdiff = (average Tahiti MSLP for the month) - (average Darwin MSLP for the month), Pdiffav = long term average of Pdiff for the month in question, and SD(Pdiff) = long term standard deviation of Pdiff for the month in question.
The multiplication by 10 is a convention. Using this convention, the SOI ranges from about –35 to about +35, and the value of the SOI can be quoted as a whole number. The SOI is usually computed on a monthly basis, with values over longer periods such a year being sometimes used. Daily or weekly values of the SOI do not convey much in the way of useful information about the current state of the climate, and accordingly the Bureau of Meteorology does not issue them. Daily values in particular can fluctuate markedly because of daily weather patterns, and should not be used for climate purposes. A table of monthly SOI values is available here. Approximate 30-day values are often included in the weekly El Niño Wrap-Up.
I don't know about various parts of Aus but I know that here across the ditch in Auckland NZ it means the pervaling SW breeze is being replaced with a NE breeze. And appartently it means more sun as well. I don't know what effects it has on wind strength as we never have any wind anyway.
Now just going back to my Uni meteorology courses. - 1) La Nina is generally causing more rain on the eastern Sea board which is not good for NE Sea breezes in Sydney and/or SE in QLD./ Because the rain events are most liley to come from a wet warm onshore system in Sydney from the Southeast. Anybody in Sydney might remember back 20 years or more when October used to be the wet month and we'd get those miserbale SE drizzle days and also I remeber when it would rain for two weeks solidly in School holiday in JAN. The last siginificant La Nina was in 90-91 when we had 16 consecutive wet weekends in a row.
Drought years are windier in the East - Wet years windless.
I hate to put a mocker on this season and I could be very wrong because there are other factors that have changed wind patterns over the last 20 years like growing Urban development which reduced evapotranspiration rates.
this la nina crap is causing havoc in our region...the worst monsoon winds to date it's either little wind or extreme..and the rains it's flooding almost all parts here...am sure the tradewinds or the opposite would be more fiercer and consistent...cheers
