Friday, March 27, 2009
Thundershowers seen dousing mercury in north
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.
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.
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.
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
Model forecasts indicate normal monsoon this year
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.