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Author Topic: What is the dipole?  (Read 4507 times)

Offline rhade

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What is the dipole?
« on: 18/02/2009 16:05:25 »
I heard that the recent Australian bushfires may have been exacerbated by the Indian Ocean Dipole. Can anyone explain what this is? I only know it's something to do with climatic events.


 

Offline frethack

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What is the dipole?
« Reply #1 on: 18/02/2009 16:22:53 »
I dont know much about the IOD, but this comes from the Japan Agency for Marine-Earth Science and Technology
http://www.jamstec.go.jp/frsgc/research/d1/iod/

Quote
The Indian Ocean Dipole
The Indian Ocean Dipole (IOD) is a coupled ocean-atmosphere phenomenon in the Indian Ocean. It is normally characterized by anomalous cooling of SST in the south eastern equatorial Indian Ocean and anomalous warming of SST in the western equatorial Indian Ocean. Associated with these changes the normal convection situated over the eastern Indian Ocean warm pool shifts to the west and brings heavy rainfall over the east Africa and severe droughts/forest fires over the Indonesian region.

Schematic of a positive IOD event.    

Schematic of a negative IOD event.
   
SST anomalies are shaded (red color is for warm anomalies and blue is for cold). White patches indicate increased convective activities and arrows indicate anomalous wind directions during IOD events.
The name " Indian Ocean Dipole (IOD) " was coined by Prof. Yamagata, Dr. Saji and other researchers of the Climate Variations Research Program (CVRP) of Frontier Research Center for Global Change (FRCGC) to represent the zonal dipole structure of the various coupled ocean-atmosphere parameters such as SST, OLR and Sea Surface Height anomalies. Generally, this configuration is also called positive IOD. Infact, a negative IOD also evolves preceding/following a positive IOD, with reverse in the configuration of the positive IOD.
 

paul.fr

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What is the dipole?
« Reply #2 on: 18/02/2009 16:57:59 »
A good place to start would be CSIRO, they have been doing some research into the IOD and it's affects on the Australian climate. I think the IOD 'should' be a cause of concern to climate maodellers, as I think it bucks the trend and also predictions based around el nino and la nina events (ENSO). NOAA and NWS should have more information on ENSO than the Australian BOM.
 

paul.fr

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What is the dipole?
« Reply #3 on: 18/02/2009 17:12:04 »
a QUICK LOOK ON bom, GIVES THIS:

http://www.bom.gov.au/climate/coupled_model/about-POAMA-outlooks.shtml#IOD

The POAMA System

POAMA stands for Predictive Ocean Atmosphere Model for Australia. POAMA is a climate model system used for seasonal to interannual predictions. It consists of coupled ocean-atmosphere general circulation models along with sophisticated data assimilation and land-surface initialisation systems. POAMA was developed jointly by the Bureau of Meteorology and CSIRO Marine Research and is under continual development. POAMA forecasts of the state of El Nio - Southern Oscillation (ENSO) are issued daily by the National Climate Centre. Full details of the POAMA system and many trial products can be found on the official POAMA site.
POAMA forecasts

Each day a new POAMA forecast is performed. The ocean, atmosphere and land surface are initialised with the most up-to-date observations. The POAMA model is then run to simulate the ocean and atmosphere conditions of the next nine months. Each daily forecast therefore differs slightly in the initial state of the climate system. The variability of the results among forecasts gives an indication of the uncertainty in the future evolution of the climate system. When many individual forecasts are considered together they are said to comprise an ensemble and the spread in the conditions they forecast can be used to quantify the probability distribution of future conditions.

Generally the outlooks given on these pages are based on an ensemble of the 30 most recent POAMA forecasts. The start dates of each of these 30 forecasts are one day apart.
ENSO forecasts

The National Climate Centre (NCC) uses the NINO3 index to monitor the state of ENSO. An El Nio (warm) event is considered to occur when the NINO3 index exceeds +0.8C, which is about one standard deviation. Similarly a La Nia (cold) event occurs when NINO3 is less that −0.8C. POAMA forecasts of NINO3 are given out to eight months ahead to monitor the possible evolution of ENSO conditions. Similar forecasts of both NINO3.4 and NINO4 are also shown to monitor the details of possible future ENSO conditions.

Two types of plots are used to show POAMA forecasts of NINO indices: "plumes" showing an ensemble of individual forecasts of the index for the next eight months, and frequency distributions among the ensemble of the indices for each month in the forecast period.
Indian Ocean Dipole forecasts

Another region of SST variability that impacts on Australian climate is the Indian Ocean. One mode of variability that appears to affect Australian rainfall, particularly the south east of the country, is the Indian Ocean Dipole (IOD). The IOD referred to here is defined by an index that is the difference between SST in the western (50-70E, 10S-10N) and eastern (90-110E, 10-0S) tropical Indian Oceans. A positive IOD occurs when the western basin is warmer than average and the eastern basin is cool and hence the IOD index is positive. These regions were proposed in a paper by Saji et al. (1999) on the Indian Ocean Dipole that showed a modulation in Australian seasonal rainfall with IOD positive and negative years. The influence of some modes of Indian Ocean SST variability on Australian climate is explicitly included in the model that produces the statistical Seasonal Climate Outlooks.

As with the NINO indices, POAMA forecasts of the IOD are given as averages of the monthly IOD index, plumes of the spread and frequency distributions of positive/neutral/negative IOD out to nine months for the ensemble of the 30 most recent forecasts. A positive IOD is defined here if the index is greater than +0.4C, a negative IOD if the index is less than −0.4C. The standard deviation of the monthly-mean IOD index averages about 0.4C.
Saji N.H., B.N. Goswami, P.N. Vinayachandran, T. Yamagata, 1999: A dipole mode in the tropical Indian Ocean. Nature, 401, 360-363.

although if you listen to, or read Tim Flannery then it's all down to climate change...

http://www.guardian.co.uk/environment/2009/feb/10/australia-bush-fires

The day after the great fire burned through central Victoria, I drove from Sydney to Melbourne. For much of the way indeed for hundreds of miles north of the scorched ground - smoke obscured the horizon, entering my air conditioned car and carrying with it that distinctive scent so strongly signifying death, or to Aboriginal people, cleansing.

It was as if a great cremation had taken place. I didn't know then how many people had died in their cars and homes, or while fleeing the flames, but by the time I reached the scorched ground just north of Melbourne, the dreadful news was trickling in. At first I heard that 70 people had died, then 108. Then 170. While the precise number of victims is yet to be ascertained, the overall situation at least is now clear. Australia has suffered its worst recorded peacetime loss of life. And the trauma will be with us forever.

I was born in Victoria, and over five decades I've watched as the state has changed. The long, wet and cold winters that seemed so insufferable to me as a young boy wishing to play outside vanished decades ago, and for the past 12 years a new, drier climate has established itself. I could measure its progress whenever I flew into Melbourne airport. Over the years the farm dams under the flight path filled ever less frequently, while the suburbs crept ever further into the countryside, their swimming pools seemingly oblivious to the great drying.

Climate modelling has clearly established that the decline of southern Australia's winter rainfall is being caused by a build-up of greenhouse gas, much of it from the burning of coal. Ironically, Victoria has the most polluting coal-fed power plant on Earth, while another of its coal plants was threatened by the fire. There's evidence that the stream of global pollution caused a step-change in climate following the huge El Nio event of 1998. Along with the dwindling rainfall has come a desiccation of the soil, and more extreme summer temperatures.

This February, at the zenith of a record-breaking heatwave with several days over 40C, Melbourne recorded its hottest day ever a suffocating 46.4C, with even higher temperatures occurring in rural Victoria. This extreme coincided with exceptionally strong northerly winds, which were followed by an abrupt southerly change. This brought a cooling, but it was the shift in wind direction that caught so many in a deadly trap. Such conditions have occurred before. In 1939 and 1983 they led to dangerous fires. But this time the conditions were more extreme than ever before, and the 12-year "drought" meant that plant tissues were almost bone dry.

Despite narrowly missing the 1983 Victorian fires, and then losing a house to the 1994 Sydney bushfires, I had not previously appreciated the difference a degree or two of additional heat, and a dry soil, can make to the ferocity of a fire. This fire was quantatively different from anything seen before. Strategies that are sensible in less extreme conditions, such as staying to defend your home or fleeing in a car when you see flames, become fatal options under such oven-like circumstances. Indeed, there are few safe options in such conditions, except to flee at the first sign of smoke.

My country is still in shock at the loss of so many lives. But inevitably we will look for lessons from this natural tragedy. The first such lesson I fear is that we must anticipate more such terrible blazes in future, for the world's addiction to burning fossil fuels goes on unabated, with 10 billion tonnes being released last year alone. And there is now no doubt that the pollution is laying the preconditions necessary for more such blazes.

When he ratified the Kyoto protocol, Australia's prime minister Kevin Rudd called climate change the greatest threat facing humanity. Shaken, and clearly a man who has seen things none of us should see, he has now had the eye-witness proof of his words. We can only hope now that Australia's climate policy, which is weak, is significantly strengthened.

After ignoring the Kyoto protocol for years, just months ago we committed to a reduction in pollution of a mere 5% by 2020 over 2000 levels, with the possibility of increasing that to 15% if a successful treaty comes out at Copenhagen later this year. Our national goal is a 60% reduction in emissions by 2050, but such targets are easy to articulate if the bulk of the work must be done by future governments.

As the worst greenhouse polluters, per capita, of any developed nation, there is an urgent need for Australians to reduce our dependency on coal. I believe that if we want to give ourselves the best chance of avoiding truly dangerous climate change, we should cease burning coal conventionally by around 2030. No such policy is currently being contemplated. Instead, as perhaps anyone would, Australians have been focusing on the immediate cause of some of the fires.

Rudd has said that the arsonists suspected of lighting some fires are guilty of mass murder, and the police are busy chasing down these malefactors. But there's an old saying among Australian fire fighters "whoever owns the fuel, owns the fire". Let's hope that Australians ponder the deeper causes of this horrible tragedy, and change our polluting ways before it's too late.

Tim Flannery is a scientist at the University of Macquarie and author of The Weather Makers: The History and Future Impact of Climate Change
 

Offline rhade

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What is the dipole?
« Reply #4 on: 05/03/2009 12:23:29 »
Thanks, guys! Yeah, I had heard about Australia being a major coal burner and polluter. Mr. Flannery paints a truly grim picture.
I imagine it's pretty hard to be certain whether the Dipole or climate change caused the wildfires. What seems certain is that the Dipole needs to be studied in greater depth, and pollution, both in Australia and the rest of the world, effectively tackled.
 

Offline rosy

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What is the dipole?
« Reply #5 on: 05/03/2009 12:51:16 »
Of course, the other theory is that the extreme severity of the wildfires was caused by the fact that, left to itself, that type of environment will have periodic fires anyway, but that these have been suppressed by human intervention... this has resulted in larger areas ready to burn off quickly at any one time and so once a fire does get out of control it will get really out of control. I'm not sure there's an answer to this, controlled burning being the oxymoron it is...
 

Offline dentstudent

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What is the dipole?
« Reply #6 on: 05/03/2009 13:17:25 »
In (almost) the words of Not the Nine O'clock News, "The only good pole, is a dipole".
 

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What is the dipole?
« Reply #6 on: 05/03/2009 13:17:25 »

 

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