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Showing posts with label Indian Ocean Dipole. Show all posts
Showing posts with label Indian Ocean Dipole. Show all posts

Thursday, May 14, 2009

{News} 090513! All dry on the western front

All dry on the western front

The Australian, May 13, 2009

IT has been labelled the cousin of El Nino, the Indian Ocean's equivalent of the climatic engine in the Pacific that drives the cycle of droughts and floods in Australia's southeast.
But when CSIRO scientist Wenju Cai factored the Indian Ocean Dipole into his climate model, he found that this little cousin could contribute to droughts. It could depress spring rainfall by up to 30 per cent in Australia's southeast, a region encompassing the nation's food bowl, the southern Murray-Darling Basin. And with global warming set to increase the frequency of dipole events, Australia was likely to get even bigger climatic shocks than previously thought, the computer simulations suggested.
Much of Australia's climatological research has focused so far on the Pacific Ocean's El Nino-Southern Oscillation pattern.
Droughts hit when the eastern Pacific warms, weakening the eastern trade winds that bear rain to southeastern Australia. La Nina episodes reverse the pattern, bringing floods to Australia.
The outlook for ENSO is bad: the past 30 years have seen the most El Nino episodes since instrumental weather records began in 1880 and the number of droughts is projected to increase as the planet warms.
However, attention has shifted in recent years to poorly understood climatic drivers operating in the Indian Ocean, and the latest results suggest that even the gloomiest predictions on drought may have been optimistic.
Cai, a climatologist with CSIRO's Wealth from Oceans national research flagship, led a research team that in 2003 uncovered the first climate modelling evidence that global warming was contributing to some of Australia's droughts. The scientists wanted to find out if climate change was affecting the winter westerlies, which deliver rain to southern Australia, including the Murray-Darling Basin.
They used a sophisticated global climate model and a supercomputer to gauge the effect of global warming on the Southern Annular Mode, the southern Indian Ocean climatic system that drives the westerlies.
When they compared climate simulations based on modern and pre-industrial greenhouse gas levels, they found that a 35-year drying trend in the southwest of Western Australia was difficult to explain by natural climatic variability alone. Global warming was probably responsible for 5 per cent to 10 per cent of the drying trend, during which average annual rainfall plummeted by 15 per cent and up to 30 per cent in some regions. And the greenhouse contribution was likely to increase.
While warming the lower atmosphere, the greenhouse effect cools the stratosphere above it, especially near Antarctica. This sets up a north-south temperature difference and therefore a pressure gradient that pushes the moisture-bearing westerlies southward, at times causing them to miss the Australian landmass.
Worryingly, the modelling suggested that the system would take 500 to 600 years to recover, even if greenhouse gas levels were stabilised.
The results came when the world was still in greenhouse denial, before the appearance of ominous signs, such as the acceleration of the Greenland glaciers and the melting of the Arctic sea ice and permafrost, which left no room for doubt that the planet was under pressure from human activity.
And they came before the Intergovernmental Panel on Climate Change handed down its fourth assessment report in 2007 that stated humans were very likely to have contributed to climate change.
However, even the worrying outlook for Australia in that report could be optimistic, Cai says. The report preceded new findings on the impact of the Indian Ocean Dipole on droughts.
A positive Indian Ocean Dipole index sounds the drought alarm bells. It occurs when the western Indian Ocean is warmer than the eastern basin. The dipole builds up in late winter and continues into September, October and November. The frequency of positive readings has increased three-fold during the past 100 years, with positive dipoles developing mainly in consecutive years.
"Each time the dipole index goes positive in consecutive years the intensity of drought is higher," Cai says. "It has contributed to an unprecedented intensity of drought. The question is whether this is the impact of global climate change."
Using global climate models, Cai's team compared scenarios to see how the Indian Ocean Dipole would respond to global warming.
The team, co-funded by the Australian Climate Change Science Program, investigated 1000 virtual years of the late 20th century in 20 virtual worlds with varying degrees of global warming, and presented its results at a recent meeting of the American Geophysical Union.
"The climate model is projecting that as we go into the future, with global warming continuing, the Indian Ocean Dipole will perhaps occur more often," Cai says. "In a warming world, the number of positive Indian Ocean Dipoles will increase by around 20 per cent."
An increase in the frequency of positive dipole events would exacerbate droughts kicked off in autumn - the critical crop-planting season, when rainfall plummets in El Nino years - and extended through winter by an awry Southern Annular Mode. It would drag the droughts into spring while increasing their severity.
Repeated droughts would dry out the Murray-Darling catchment, lessening the inflow to the ailing rivers when rain did come.
"If there's good autumn rain, the basin is soaked. If there isn't, the winter rain first has to wet the soil, and there isn't much inflow to the rivers," says Cai.
There are worrying signs that the Indian Ocean Dipole already could be out of kilter. The index went into the critical zone in the three years from 2006.
"In September 2008, southeastern Australia had the lowest rainfall on record," Cai says.


Wednesday, May 13, 2009

NASA Study Says Climate Adds Fuel to Asian Wildfire Emissions


In the last decade, Asian farmers have cleared tens of thousands of square miles of forests to accommodate the world’s growing demand for palm oil, an increasingly popular food ingredient. Ancient peatlands have been drained and lush tropical forests have been cut down. As a result, the landscape of equatorial Asia now lies vulnerable to fires, which are growing more frequent and having a serious impact on the air as well as the land.A team of NASA-sponsored researchers have used satellites to make the first series of estimates of carbon dioxide (CO2) emitted from these fires -- both wildfires and fires started by people -- in Malaysia, Indonesia, Borneo, and Papua New Guinea. They are now working to understand how climate influences the spread and intensity of the fires.Using data from a carbon-detecting NASA satellite and computer models, the researchers found that seasonal fires from 2000 to 2006 doubled the amount of carbon dioxide (CO2) released from the Earth to the atmosphere above the region. The scientists also observed through satellite remote sensing that fires in regional peatlands and forests burned longer and emitted ten times more carbon when rainfall declined by one third the normal amount. The results were presented in December 2008 in Proceedings of the National Academy of Sciences. Tropical Asian fires first grabbed the attention of government officials, media, and conservationists in 1997, when fires set to clear land for palm oil and rice plantations burned out of control. The fires turned wild and spread to dry, flammable peatlands during one of the region’s driest seasons on record. By the time the flames subsided in early 1998, emissions from the fires had reached 40 percent of the global carbon emissions for the period."In this region, decision makers are facing a dichotomy of demands, as expanding commercial crop production is competing with efforts to ease the environmental impact of fires," said Jim Collatz, an Earth scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md., and a co-author of the study. "The science is telling us that we need strategies to reduce the occurrence of deforestation fires and peatlands wildfires. Without some new strategies, emissions from the region could rise substantially in a drier, warmer future." Since the 1997 event, the region has been hit by two major dry spells and a steady upswing in fires, threatening biodiversity and air quality and contributing to the buildup of CO2 in the atmosphere. As more CO2 is emitted, the global atmosphere traps more heat near Earth’s surface, leading to more drying and more fires. Until recently, scientists knew little about what drives changes in how fires spread and how long they burn. Collatz, along with lead author Guido van der Werf of Vrije University, Amsterdam, and other colleagues sought to estimate the emissions since the devastating 1997-98 fires and to analyze the interplay between the fires and drought. They used the carbon monoxide detecting Measurements of Pollution in the Troposphere (MOPITT) instrument on NASA’s Terra satellite -- as well as 1997-2006 fire data and research computer models -- to screen for and differentiate between carbon emissions from deforestation versus general emissions. Carbon monoxide is a good indicator of the occurrence of fire, and the amounts of carbon monoxide in fire emissions are related to the amount of carbon dioxide. They also compared the emissions from different types of plant life (peat land vs. typical forest) by examining changes in land cover and land use as viewed by Terra's Moderate Resolution Imaging Spectradiometer (MODIS) and by Landsat 7.Collatz explained that two climate phenomena drive regional drought. El Niño's warm waters in the Eastern Pacific change weather patterns around the world every few years and cause cooler water temperatures in the western Pacific near equatorial Asia that suppress the convection necessary for rainfall. Previously, scientists have used measurements from NASA’s Tropical Rainfall Measurement Mission satellite to correlate rainfall with carbon losses and burned land data, finding that wildfire emissions rose during dry El Niño seasons. The Indian Ocean dipole phenomenon affects climate in the Indian Ocean region with oscillating ocean temperatures characterized by warmer waters merging with colder waters to inhibit rainfall over Indonesia, Borneo, and their neighbors."This link between drought and emissions should be of concern to all of us," said co-author Ruth DeFries, an ecologist at Columbia University in New York. "If drought becomes more frequent with climate change, we can expect more fires."Collatz, DeFries, and their colleagues found that between 2000 and 2006, the average carbon dioxide emissions from equatorial Asia accounted for about 2 percent of global fossil fuel emissions and 3 percent of the global increase in atmospheric CO2. But during moderate El Niño years in 2002 and 2006, when dry season rainfall was half of normal, fire emissions rose by a factor of 10. During the severe El Niño of 1997-1998, fire emissions from this region comprised 15 percent of global fossil fuel emissions and 31 percent of the global atmospheric increase over that period."This study not only updates our measurements of carbon losses from these fires, but also highlights an increasingly important factor driving change in equatorial Asia," explained DeFries. "In this part of Asia, human-ignited forest and peat fires are emitting excessive carbon into the atmosphere. In climate-sensitive areas like Borneo, human response to drought is a new dynamic affecting feedbacks between climate and the carbon cycle." In addition to climate influences, human activities contribute to the growing fire emissions. Palm oil is increasingly grown for use as a cooking oil and biofuel, while also replacing trans fats in processed foods. It has become the most widely produced edible oil in the world, and production has swelled in recent years to surpass that of soybean oil. More than 30 million metric tons of palm oil are produced in Malaysia and Indonesia alone, and the two countries now supply more than 85 percent of global demand. The environmental effects of such growth have been significant. Land has to be cleared to grow the crop, and the preferred method is fire. The clearing often occurs in drained peatlands that are otherwise swampy forests where the remains of past plant life have been submerged for centuries in as much as 60 feet of water. Peat material in Borneo, for example, stores the equivalent of about nine years worth of global fossil fuel emissions. "Indonesia has become the third largest greenhouse gas emitter after the United States and China, due primarily to these fire emissions," Collatz said. "With an extended dry season, the peat surface dries out, catches fire, and the lack of rainfall can keep the fires going for months." Besides emitting carbon, the agricultural fires and related wildfires also ravage delicate ecosystems in conservation hotspots like the western Pacific island of Borneo, home to more than 15,000 species of plants, 240 species of trees, and an abundance of endangered animals. Smoke and other fire emissions also regularly taint regional air quality to such a degree that officials have to close schools and airports out of concern for public health and safety. Peat fires also aggravate air pollution problems in this region because they release four times more carbon monoxide than forest fires. In 1997, air pollution from the fires cost the region an estimated $4.5 billion in tourism and business.


Friday, March 27, 2009

{News} 090324! Thundershowers seen dousing mercury in north

Thundershowers seen dousing mercury in north

Vinson Kurian
Thiruvananthapuram, March 24 Maximum temperatures over northwest India are expected to come down by 2 to 4 degree Celsius during the next three days as thunderstorms continue to flare up eastward from the region.
The maximum temperatures are currently near normal over most parts of the country but the minimum temperatures have been hovering above normal by 2 to 5 degree Celsius over parts of northwest and central India.
The India Meteorological Department (IMD) said in its update on Tuesday that one such weather-maker system lay anchored over Jammu and Kashmir.
On Tuesday, a weather-setting trough extended from Lakshadweep area to west Madhya Pradesh through south Konkan, Goa and Madhya Maharashtra with an embedded cyclonic circulation over west Madhya Pradesh.
Another cyclonic circulation hovered over southwest Rajasthan. MOISTURE FEED
The cool westerlies to northwesterlies packing the southward dipping western disturbances and the moisture the associated warm southwesterlies scoop up from the peninsular seas combined to set up the unsettled weather zone extending from northwest and even peninsular west India right into the North-East. LA NINA OUTLOOK
Meanwhile, Dr Tony Barnston, Head-Forecasting at the International Research Institute (IRI) for Climate and Society at Columbia University, informed Business Line that La Nina outlook of 22 agencies around the world varied from one to another.
“This does not necessarily mean that the continuation of weak La Nina is unlikely to occur, but just that this is on one of the two extremes. On the other extreme, we have three dynamical models calling for El Nino development by this summer.
“Our own forecast is for La Nina to weaken to neutral ENSO conditions this month or, at the latest, during April. Our opinion is near the middle of the pack. So, in short, we do not expect it to last longer than expected,” he observed.
As for the Indian Ocean Dipole (IOD), Dr Barnston said the IRI outlook is quite neutral. “We see no particular hint that a positive IOD will develop. Since we think the La Nina will be gone by May, we do not see a strong preference for a negative IOD either,” he added.


{News} 090325! Bushfire origins lie in Indian Ocean

Bushfire origins lie in Indian Ocean
Wednesday, 25 March 2009 Dani CooperABC

A weather pattern centred on the Indian Ocean may provide an early warning system for major bushfires in southern Australia, climate experts say.

Dr Wenju Cai and Tim Cowan, of CSIRO's Marine and Atmospheric Research have uncovered a link between the Indian Ocean Dipole (IOD) and Victoria's killer bushfires.

Cai will tell the Greenhouse 2009 conference today that 11 of 16 major bushfires in Victoria since 1950 have been preceded by what is known as a positive IOD event.

He says, "an unprecedented" three consecutive positive IOD events preceeded February's devastating Black Saturday bushfires.

The IOD refers to temperature fluctuations in the east and western Indian Ocean.
In its negative phase, the IOD brings cool water to the ocean west of Australia and warm water to the north, leading to winds that bring rain-bearing air over the continent.

In the positive phase, water temperatures are reversed and less rainfall travels to Australia, particularly to Victoria where the negative IOD provides winter and spring rains.

Unprecedented dry
As part of their research, Cai and Cowan recorded changes in the IOD using Argo floats, robotic devices that measure the subsurface ocean temperature.
They found the IOD was in an "unprecedented" positive state for three consecutive years leading up to 2009.

They say this preconditioned the environment to the extent that it was almost inevitable the bushfires, which claimed more than 200 lives, would occur.
"If you look at the accumulative soil moisture in Victoria, it's unprecedented, it's never been so dry," says Cai.

The researchers also found an IOD link to the Ash Wednesday bushfires of February 1983, with a positive event reducing rainfall during the winter of 1982.
Cowan says of the 11 bushfires preceded by a positive IOD, six were coupled with an El Nino event.

But, there was only one occasion where an El Nino alone preceded a bushfire, compared to the five times when only an IOD impacted on the rainfall.
This shows the influence of the IOD was enough to precondition the environment to high bushfire risk, says Cowan.

Increased frequency
Cai and Cowan say climate change projections show the frequency of positive IOD events will increase in the future.
"Almost all climate models say under climate change we are going to have an Indian Ocean warming pattern," says Cai.
"That means it has to be manifested in either more frequent positive IOD events or higher intensity positive IODs."
According to Cai, the effects of climate change can already be seen.
Between 1900 and 1930 there were four positive IOD events, he says.
But, in the past 30 years there have been 12 positive IODs, a 400% increase.
For Victorian residents living in bushfire-prone areas that is bad news.
Cai says the continued suppression of rainfall in Victoria will only make conditions more fire friendly.
"The implication [of the research] is if we have a positive IOD in one year then the following season you have a higher bushfire risk," he says.

According to Cai this knowledge could provide an early warning system.
"It gives us four to five months' lee time [to prepare for bushfires].
He says modeling shows that climate change will also lead to a 30% increase in the number of consecutive events, while the odds of three consecutive IODs occurring increases by 300%.
"In 1000 virtual years without climate change we get two occurrences [of three consecutive positive IOD events].
"With climate change factored into the modeling this becomes eight."


Sunday, March 22, 2009

{News} 090322! Model forecasts indicate normal monsoon this year

Model forecasts indicate normal monsoon this year

Vinson Kurian
Thiruvananthapuram, March 22 The International Research Institute (IRI) for Climate and Society at Columbia University has forecast normal to slightly above normal monsoon for India during June to September this year.

This would be preceded by a spectacular pre-monsoon season, especially towards the East and northeast of the country, a comparative study of predictions by IRI and other models suggested.
The IRI has also predicted above normal temperatures for North India during the April-May-June quarter, which is crucial for ‘setting up the monsoon’. The land-ocean temperature differential is the driving force behind the monsoon.

The May-June-July quarter witnesses the onset of monsoon orchestrated by the Arabian Sea arm along the Southwest coast and the Bay of Bengal over the northeastern States.
IRI forecasts indicate a busy onset phase over the northeast, coming close on the heels a successful pre-monsoon season. Nagaland-Manipur-Mizoram-Tripura, Assam and Meghalaya, along with adjoining Bangladesh and Myanmar, may benefit.

But the onset along the southwest coast (over Kerala) is being seen as a more sober affair, though a blow-up of rains is indicated for coastal Karnataka and the Konkan coast.
June-July-August would see normal rains all over the country. During the last year, the rains had failed this crucially important phase leading to destruction of the sugar and cotton crops.
Independent forecasters warned that the weak but prevailing La Nina conditions in the equatorial Pacific and a still evolving Indian Ocean Dipole (IOD) could combine to totally undo the best forecasts.

In a La Nina, ocean temperatures cool down in the equatorial and equatorial-east Pacific while a corresponding warming anomaly propagates to the west. Associated convection and storm development are traditionally found to favour a good Indian monsoon but without any direct cause-effect relationship.

An IOD refers to the see-sawing of temperatures in the West and East Indian Ocean, and has a more immediate effect on the performance of the monsoon.

A positive IOD (warming anomaly in the West Indian Ocean) amplifies the performance of the monsoon, as has been the case during the last three years, a rare occurrence by itself. Excess showers over the west coast and adjoining central India is a signature feature associated with a positive IOD.

Both the Indian Ocean and the equatorial Pacific oceans are being scanned for possible signs of season-altering trends with respect to specific parameters.

In any case, the IRI has ventured to suggest that the four-month season would end in a flourish during the last quarter of July-August-September. The west coast and adjoining central peninsula extending to some parts of north and northwest India are expected to witness excess rains during this phase.

Mr Jing-Jia Luo, Senior Scientist at the Tokyo-based Climate Variations Research Program Frontier Research Centre for Global Change, informed Business Line that the current La Nina may persist until the year-end.

Mr Luo has also forecast that a negative IOD may spring up during the second half of the year. Unlike a positive IOD, a negative IOD is usually weak and might have less influence on monsoon.
Again, the net effect of La Nina-negative IOD might depend on the strength of each signal. If the La Nina were to persist, it would have a positive impact on the monsoon.

“While current trends are suggestive of a weak La Nina lasting until the end of the year, it is advised that we wait for another month just to make sure,” he added as a word of caution.
“Model forecasts for June to August do show more rainfall for many parts of India, in particular, western India. Low-level wind behaviour too rules out a weak monsoon. To sum up, I would expect stronger than normal monsoon this summer,” Mr Luo said.


Monday, March 09, 2009

{News}090205! Indian Ocean is drought culprit

Indian Ocean is drought culprit

Ben Cubby, Environment ReporterFebruary 5, 2009
THE main cause of our droughts and flooding rains has been traced to the waters of the Indian Ocean, according to a new report from the University of NSW which could overturn decades of weather research.
The study shows that the cycle of El Nino and La Nina events, which have long been thought to play a major role in south-east Australia's weather patterns, are in fact less important than the Indian Ocean.
It is likely to have major implications for predicting rainfall in the Murray-Darling region - still in the grip of the most severe drought on record - by giving farmers tip-offs about rainfall increases six months in advance.
The current Indian Ocean warming pattern is unprecedented and probably related to climate change, researchers say.
The report found that a phenomenon known as the Indian Ocean dipole plays a dominant role in determining temperature and rainfall in south-east Australia.
It examined data on changes in the distribution of warm and cool water and found a direct correlation between dipole events and the current drought, as well as the devastating centenary drought between 1895 and 1902 and the so-called World War II drought of 1937-45.
"There really is that opportunity to improve seasonal forecasting and seasonal predictions due to these findings, because the Indian Ocean dipole is predictable several months in advance," said the lead author, Dr Caroline Ummenhofer.
During a "negative" Indian Ocean dipole, cooler winds carry moisture in south-eastern Australia. During a "positive" dipole, warmer, dryer winds limit rainfall and contribute to high temperatures. In the past three years there have been successive positive cycles.
"This is something new. This has never, in the historical record, happened before," Dr Ummenhofer said. "So there are some indications that positive Indian Ocean dipole events are becoming more frequent and negative events are becoming less frequent."
The dominant role of the Indian Ocean explains why the La Nina event, which usually brings more rain, failed to break the drought when it last occurred in 2007.
"If these Indian Ocean dipole events do follow the trend [of more positive and fewer negative events], this is a terrible piece of information for the Murray-Darling Basin," said Professor Matthew England, co-director of the Climate Change Research Centre.
The Bureau of Meteorology said the findings, from the University of NSW with help from researchers at the CSIRO and the University of Tasmania, confirmed a growing belief in the Indian Ocean's significant role in determining the weather in south-east Australia.
In the past fortnight, the bureau said many temperature records had not so much been broken as smashed, as the southern states endured the heatwave. "Normally you see records broken by a fraction, but in Tasmania for example, the record at one station went by nearly 2 degrees," said Dr David Jones, head of the bureau's National Climate Centre.
The Murray-Darling Basin Authority's quarterly update yesterday showed the drought there is worsening. Toxic algae blooms are expected, water storage is down by two-thirds and decent rain is months away.


Tuesday, March 03, 2009

{News} Atmospheric scientists trace the human role in Indonesian forest fires

Atmospheric scientists trace the human role in Indonesian forest fires

TORONTO, ON – Severe fires in Indonesia – responsible for some of the worst air quality conditions worldwide – are linked not only to drought, but also to changes in land use and population density, according to a new study in Nature Geoscience led by Robert Field of the University of Toronto.

"During the late 1970s, Indonesian Borneo changed from being highly fire-resistant to highly fire-prone during drought years, marking the period when one of the world's great tropical forests became one of the world's largest sources of pollution," says Field, a PhD student of atmospheric physics. "Ultimately, this abrupt transition can be attributed to rapid increases in deforestation and population growth. The resulting occurrences of haze currently rank among the world's worst air pollution episodes, and are a singularly large source of greenhouse gas emissions."

Sumatra has suffered from large fires at least since the 1960s, but Indonesian Borneo seems to have been resistant to large fires – even in dry years – until population density and deforestation increased substantially and land use changed from small-scale subsistence agriculture to large-scale industrial agriculture and agro-forestry.

"We've had a good understanding of fire events since the mid 1990s, but little before this due to the absence of fire data from satellites," says Field, who collaborated with Guido van der Werf of VU University Amsterdam and Sam Shen of San Diego State University. "However, one of the major impacts of large-scale fires is a reduction in visibility due to the smoke produced. Visibility is recorded several times a day at airports in the region, and these records proved to be an excellent indicator of severe fire activity. We were able to piece together visibility observations back to the 1960s, and hence develop a longer term record of the fires."

Having a long-term record of the fires allowed the scientists to better understand their causes. "Using weather records, we were able to estimate the specific rainfall level below which large fires have occurred in the previous two decades. In turn, we found that the rainfall over Indonesia was influenced equally by the Indian Ocean Dipole and the El Niño Southern Oscillation phenomena. Hopefully, this information can be used to better anticipate and prevent future haze disasters in Indonesia."

Field says that there is a direct link between the increased prevalence of severe fires and haze disasters and the man-made change in land use. "The visibility record also showed, quite strikingly, the impact of human settlement on a previously pristine tropical forest. This should give pause to further agro-forestry expansion in Indonesia, particularly for oil palm as a source of biofuel."


Wednesday, December 24, 2008

Pacific indicators point to la nina: bureau
December 23, 2008, Weekly Times
A CONTINUED cooling of the equatorial Pacific in the past two weeks raises the possibility of indicators reaching levels of a la nina, often associated with above-average rainfall in Australia, the Bureau of Meteorlogy says.

If a la nina develops, summer crops such as sorghum and cotton in northeast Australia might experience several rainfall events in the coming months, potentially boosting production. Already, these cropping areas in northern New South Wales and southern Queensland received above-average November rainfall. "Given current conditions and recent trends, the development of a la nina during the southern summer can't be ruled out. However, the majority of climate models forecast neutral conditions, with a cooler than normal Pacific, during the first quarter of 2009," the bureau said in a regular review of Pacific conditions. The bureau also cited persistently stronger than normal trade winds for some months in the western Pacific and cloudiness suppressed along much of the central and eastern equatorial Pacific.

Its Southern Oscillation Index has remained strongly positive since late August. The value of the SOI in the 30 days ended December 21 was +13, falling a little from +17 in November. Sustained positive values of the SOI are associated with a la nina. Historically, it is unusual for la nina thresholds to be reached during the southern summer, though this did occur as recently as the summer of 1999/2000, it said.

The bureau also reiterated the Indian Ocean Dipole is neutral and is expected to remain neutral through summer. The bureau previously identified a positive mode for the IOD as a key influence for a drought in 2007 that wrecked winter crops including wheat in southeast Australia. A positive mode for the IOD is an effect that often hinders the formation of the northwest cloudbands that are an important source of winter/spring rainfall in southeast Australia.


Wednesday, November 26, 2008

{News} 081125! Bay depression may intensify, to cross TN coast

Bay depression may intensify, to cross TN coast

The Hindu Business Line, Nov 25, 2008
Vinson Kurian

Thiruvananthapuram, Nov. 25 The well-marked low-pressure area over north Sri Lanka and adjoining southwest Bay of Bengal has concentrated into a depression and lay centred 200 km southeast of Pamban and about 300 km south-southeast of Nagapattinam on Tuesday afternoon.

India Meteorological Department (IMD) expected the system to intensify further and move slowly in a northwesterly direction and cross Tamil Nadu coast by Wednesday night. International models seemed to delay the landfall until Thursday along the Pattukottai-Vedaranyam belt.

Heavy to very heavy falls and isolated extremely heavy falls are likely over coastal Tamil Nadu during the next two days. Isolated heavy to very heavy falls are also likely over interior Tamil Nadu and Kerala during the same period.

Squally winds speed reaching 45-55 km/hr gusting to 65 km/hr are likely along and off the Tamil Nadu and Puducherry coasts. Sea condition is rough to very rough along and off Tamil Nadu coast. Fishermen are advised not to venture out.

Meanwhile, the US Joint Typhoon Warning Centre (JTWC) upgraded as good the potential of the system off Sri Lanka and extreme south Indian peninsula to develop into a tropical cyclone.

The threat of vertical wind shear (that kills building storms) was assessed as moderate to low on Tuesday. A limiting feature could be the proximity to land – especially since the system is shown to enter Tamil Nadu in the neighbourhood. But conversely, extended stay over seawaters and ensuing moisture feed could help crank up system strength.

A welcome result could be that the heavy rains would have cooled down the seawaters, denying purchase for an incoming easterly wave to grow to cyclonic strength.
Earlier forecasts by the Fleet Numerical Meteorology and Oceanography Centre of the US had indicated that a powerful system could be in the making as the easterly wave made inroads into the Bay waters.

Dr Swadhin Behera, Sub-Leader, Climate Variations Research Programme at the Tokyo-based Frontier Research Centre for Global Change (FRCGC), Japan Agency for Marine-Earth Science and Technology, informed Business Line that the northeasterlies are usually strong in northeast and parts of peninsular India during winter monsoon following a positive Indian Ocean Dipole (IOD) event.

The FRCGC team discovered the IOD event, which refers to sea-surface temperature differential between southwest and east Indian Ocean. A positive IOD features warmer seawaters to the southwest, which aids precipitation over India.

“So, those regions are expected to receive above normal rainfall. Eastern parts of Sri Lanka would also receive heavy rain following the positive IOD,” Dr Behera said.

“We have not done a detail analysis, but winter rains in northwest India tend to be weaker during a La Nina that is persisting in the equatorial Pacific. However, the surface temperature is usually colder than normal in such cases.

“So, relative to the passing of western disturbances, we may expect occasional heavy snow/severe cold waves in Jammu and Kashmir and the northern hills this season,” Dr Behera added.


Tuesday, November 18, 2008

{Paper} 081116! Recent intensification of tropical climate variability in the Indian Ocean

Recent intensification of tropical climate variability in the Indian Ocean

Nature Geoscience Published online: 16 November 2008 doi:10.1038/ngeo357
Nerilie J. Abram1,2, Michael K. Gagan1, Julia E. Cole3, Wahyoe S. Hantoro4 & Manfred Mudelsee5

The interplay of the El Niño Southern Oscillation, Asian monsoon and Indian Ocean Dipole (IOD)1, 2, 3 drives climatic extremes in and around the Indian Ocean. Historical4, 5 and proxy6, 7, 8, 9 records reveal changes in the behaviour of the El Niño Southern Oscillation and the Asian monsoon over recent decades10, 11, 12. However, reliable instrumental records of the IOD cover only the past 50 years1, 3, and there is no consensus on long-term variability of the IOD or its possible response to greenhouse gas forcing13. Here we use a suite of coral oxygen-isotope records to reconstruct a basin-wide index of IOD behaviour since AD 1846. Our record reveals an increase in the frequency and strength of IOD events during the twentieth century, which is associated with enhanced seasonal upwelling in the eastern Indian Ocean. Although the El Niño Southern Oscillation has historically influenced the variability of both the IOD and the Asian monsoon3, 8, 10, we find that the recent intensification of the IOD coincides with the development of direct, positive IOD–monsoon feedbacks. We suggest that projected greenhouse warming may lead to a redistribution of rainfall across the Indian Ocean and a growing interdependence between the IOD and Asian monsoon precipitation variability.


Monday, November 17, 2008

{News} 081117! Coral study points to more harsh droughts

Coral study points to more harsh droughts
17/11/2008 8:52:00 AM, The Canberra Times

New coral records have revealed Australia is likely to experience more frequent and intense droughts.

Scientists studying the tropical weather patterns stored in corals have discovered climate variability in the Indian Ocean has intensified during the 20th century. This suggests Australia and the region can expect less rain while eastern Africa gets wetter.

An international research team, led by the Australian National University, analysed corals from tropical waters north-east of Australia to build a picture of climate change going back to 1846.
Their findings are published in the journal Nature Geoscience, available online today.
To date, reliable records of the Indian Ocean Dipole a climate phenomenon similar to El Nino go back about 50 years.

Palaeoclimatologist Mike Gagan, of the ANU's Research School of Earth Sciences, said the researchers' techniques allowed them to analyse sea-surface temperature and salinity stretching back hundreds, even thousands, of years.

Indian Ocean Dipole events occur when the ocean temperature and winds along the equatorial Indian Ocean reverse from their normal state. These changes bring drought to western Indonesia and southern Australia and heavy rains to eastern Africa and southern India.

Dr Gagan said the frequency of dipole events was increasing. ''In the last 160 years, there's been about 21 dipole events that we can see, and there's only been about five very strong events,'' he said.

''But it turns out, four out of the five very strong events have occurred since 1960, and three of the very strong events have occurred since 1994.''
Dr Gagan said this meant farmers across southern Australia would not be able to rely on spring rains as they might have in the past.

''We have one dipole event every four years now on average. Who knows, there may be one every two years in 30 or 40 years,'' he said.
The researchers analysed giant porite corals, some aged 400 years, to glean information about past conditions. They drilled cores from the centre of the coral and studied the chemistry preserved in the skeleton of the coral.

''In trees, you get annual growth bands. In coral, you get annual changes in coral density, and you can count these annual density bands to keep track of the time,'' Dr Gagan said. ''We analyse it virtually month by month.''

He said the Indian Ocean Dipole was like ''the canary in the mine of climate change''.
But there was hope. ''If we can even level off CO2 and get it to be stable, even if it's a higher level, we might not like the climate that we have, but at least it's going to be more predictable and easier to adapt to,'' Dr Gagan said.


{News} 081117! Droughts to become more frequent, severe: researchers

Droughts to become more frequent, severe: researchers
ABC News, Mon Nov 17, 2008

Canberra scientists say they have proven that the world's climate is changing faster than ever before.
The international research team drilled core samples from living corals off the Indonesian coast and found an increased frequency in the weather phenomenon known as the "Indian Ocean Dipole".
Like the El Nino weather effect, the Indian Ocean Dipole has a dramatic impact on the Australian climate, and can cause severe droughts.
Australian National University researcher Dr Mike Gagan says his coral samples show the dipole is occurring more regularly and that is changing Australian weather patterns.
"There's going to be not only more propensity for drought, there's going to be more variability," he said.
"If you get a dipole event superimposed onto an El Nino event, what may be a moderate El Nino event turns out to be a very strong drought."
Dr Gagan says the Dipole used to occur every 20 years, but is now happening about every four years.
He says Australia is in for more severe droughts in coming years.
"Now that we have a 160-year record we can see a clear trend towards more frequent dipole events," he said.
"When you look at what the climate models are telling us should happen as you warm the planet, a stronger Indian Ocean Dipole is something that climate models predict."


Thursday, October 30, 2008

Sumatra and Java Satellite Images! 30 Oct 2008

{News} 081031! Drought woes to continue: Jamstec

Drought woes to continue: Jamstec

Weekly Times, October 31, 2008

BLEAK is the only way to describe Japanese forecasters' latest outlook for southeast Australia.
"Large parts of Australia will still suffer from the long-lasting drought (until) the end of this year," according to Japan's Frontier Research Center for Global Change, Jamstec.
Jamstec senior scientist Jing-Jia Luo said the group's Sintex computer model showed conditions would remain dry until January in southern Australia.

"Early next year, good rain might occur in association with the demise of IOD (Indian Ocean Dipole) and weak cooling in the central equatorial Pacific," Mr Jing-Jia said.
The Jamstec team, led by Prof Toshio Yamagata, has predicted the last three positive IOD events.

The group's most accurate modelling is based on pooled three-month outlooks across the Pacific and Indian oceans.
The Jamstec team produces monthly forecasts that show southeast Australia will experience a relatively dry October, some rain in November and a dry December.
The only month showing any promise of significantly higher than above-average rainfall is January.

Bureau of Meteorology climate analyst David Jones said the present three-year run of positive IODs was unprecedented.
"The sequence of the last three years has been very odd," Dr Jones said. "It's something we've not seen before. There's a real worry this is one of the things we expect with global warming."
Dr Jones said international climate-change models showed positive IODs and El Nino events becoming more frequent, in response to rising greenhouse gas levels.
But he said only a few of the numerous computer models predicted anything as severe as the last three years in southern Australia.

"Our climatic system is behaving very oddly," he said.
"We've had a decline in autumn rainfall in the past 30 years. Now we've had a sequence in the last five to six years where spring rain has declined. It's too early to call a trend, but it's a very odd pattern."

When the IOD is positive the sea surface temperatures around Indonesia and northern Western Australia are cooler than average. The cooler conditions reduce sea-surface evaporation, and moisture in the atmosphere. Reduced atmospheric moisture leads to a slump in the formation of crucial northwest cloud bands that sweep across the continent to deliver rain to southeast Australia.


Tuesday, October 28, 2008

{News} 081029! Models raise the mercury

Models raise the mercury
29/10/2008 9:15:00 AM, FairFax Digital

CENTRAL Victoria is bracing for another hot summer, with the Bureau of Meteorology's latest outlook indicating higher than average temperatures through to January.
Higher daytime and night-time temperatures look set to exacerbate an already dry spring and cause more water losses through evaporation.
The latest climatic outlook based on modelling of ocean temperatures shows a probability of up to 70 per cent that daytime temperatures will exceed the median from November to January.
The probability in relation to night-time temperatures is as high as 80 per cent.
However, the silver lining is that rainfall outlooks don't show any strong tendency to be below or above average.
Even average rain of about 110mm over the next three months would be a blessing.
The two-month spring rainfall total in Bendigo is only 15mm, so it is tracking to be one of the worst on record.
Climatologist Robyn Gardiner said the strongest influence on the outlook was the warming trend of the Indian Ocean off Western Australia.
Modelling showed a possible increase in northerly airflows from the centre of the continent.
At the same time Pacific Ocean temperatures, which most directly influenced the El Nino and La Nina patterns, remained neutral - continuing the indications of a one-year interval between the events.
However, from a rainfall perspective it is the weakening of the Indian Ocean dipole that brings the most positive news to Victoria.
The IOD is caused by cooler water in the Indonesian and eastern Indian Ocean blocking the generation of moisture-laden air, which historically has given Victoria much of its spring rainfall.
Ms Gardiner said modelling showed the indicators had faded from a peak in August and September and were reverting to normal.
CSIRO principal research scientist Dr Wenju Cai, a specialist in marine and atmospheric research, believes the dipole has been an important element in the recent failure of spring rains.


Sunday, October 19, 2008

{Annoucement} 081008! ENSO Wrap-up

ENSO Wrap-up

BOM, Oct 8, 2008

Summary: Neutral ENSO conditions to continue
The overall state of the climate in the Pacific Basin remains neutral with respect to ENSO. The eastern tropical Pacific Ocean has shown further cooling over the past fortnight, with surface temperatures now close to their long-term average. Also, recent cooling in the subsurface indicates the possibility of a further surface cooling over the coming weeks, especially in the eastern Pacific. This cooling has been largely driven by stronger than normal trade winds over the central and western equatorial Pacific during September. The SOI, although slightly weaker than two weeks ago, remains positive at +10.
Given current conditions and trends in the equatorial Pacific there is now little potential for an El Niño event to occur in 2008. Historically, there is a strong tendency for the phase of ENSO to remain constant through the southern spring; therefore a switch to La Niña conditions is also very unlikely. This is supported by climate model forecasts, which show neutral conditions are likely to remain until the end of the year. The Indian Ocean Dipole is following its normal cycle of decay in the spring and is currently close to zero.


{News} 081015! Climate's three-headed dog

Climate's three-headed dog

Farmonline, 15/10/2008 2:10:00 PM
There's a "three-headed dog" savaging Australia's climate, according to CSIRO scientist Dr Wenju Cai, and two of the heads are eating away at rainfall in southern Australia.
The three climate influences referred to by Dr Cai are El Nino, the Southern Annullar Mode, and the Indian Ocean Dipole.
All are driven by ocean temperatures, and all are being intensified, to Australia's disadvantage, by global warming.
El Nino, driven by temperatures in the Pacific Ocean, is well studied and has had fairly predictable consequences for mid-latitude eastern Australia.
The other two influences are less well known, but Dr Cai said there is growing evidence that their fluxes are behind the drying-out of southern Australia.
One, Southern Annular Mode (SAM), appears to be driving rain-bearing winter fronts progressively out into the Southern Ocean.
To the west, the Indian Ocean Dipole (IOD) is blocking the generation of moisture-rich air that crosses the continent to bring Victoria, South Australia and southern NSW vital spring rains.
Dr Cai, a principal research scientist with CSIRO Marine and Atmospheric Research, believes that it's the IOD that is behind the failed spring rains currently causing stress to farmers in the south-east.
In a "good" year, the eastern Indian Ocean lying off Western Australia is warmer than the ocean off Africa.
The warmth produces convection, and humid pressure systems that stream across to south-eastern Australia where, on meeting cold air from the south, they produce rain.
When the eastern Indian Ocean is cool, convection dies away and south-eastern Australia (mainly Victoria and South Australia) can expect less spring rain.
According to Dr Cai, the IOD is now at work with rare savagery.
"During 2006-07-08, we've had a very unusual situation in that three Indian Ocean Dipoles occurred consecutively," Dr Cai said.
"The only time we've known this to occur before is in 1944-45-46. From 1939-46 were big drought years.
"The polar shift of the fronts [SAM] is also going on, but these consecutive dipole events are making that very much worse."
Modelling, and trends to date, indicate that as atmospheric carbon dioxide rises, warming patterns in the Indian Ocean will be "dipole-like", Dr Cai said — that is, the phenomenon is likely to be more frequent.
Unusually in the world of modelling, all nine major climate models agree on SAM.
The theory, according to Dr Cai, is that as the planet warms, the big rain-bearing fronts that deliver southern Australia much of its winter rain are progressively tracking further south, out to sea.
Frontal systems are always moving west-to-east across the upper reaches of the Southern Ocean, shifting around the globe in a broad band defined by ocean temperature.
SAM refers to the seasonal north-south movement in those fronts as oceans warm and cool with the seasons.
In summer, with the warming of the oceans that share a latitude with southern Australia, the weather systems move south, tending to track across the ocean.
In winter, as the cool temperature gradient moves north again, so do the fronts.
Historically, their winter track has been over southern Australia, delivering the south much of its characteristic winter rainfall.
But Dr Cai said that as climate change and ozone depletion warms the planet's oceans from the equator down, the ocean temperature gradient is changing.
As the temperature rise creeps south, it takes these rain-bearing systems south - not just in summer, but in winter too.
"This is the most consistent result we see in the computer models," Dr Cai said.
"The only possibility for stopping it is to stabilise levels of atmospheric carbon dioxide and stop the change in ocean temperature gradient."
And even then, he added, it might take hundreds of years for patterns to re-establish themselves to those of the recent past.
"I don't have any good news," Dr Cai confessed.


Sumatra and Java Satellite Images! 19 Oct 2008

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