Exiting monsoon sets up showers over peninsula

The southwest monsoon, now on its leg over the peninsula, has been active over south interior Karnataka during the 24 hours ending Tuesday morning, an update from the Chennai Regional Met Centre said.

Forecast for the next two days said that rain or thundershowers are likely to occur at a few places over Kerala, Tamil Nadu, Puducherry, coastal and south interior Karnataka.

Isolated rain or thundershowers have been forecast over Lakshadweep, coastal Andhra Pradesh, Rayalaseema and north interior Karnataka.

COMPLETE REVERSAL

The circulation features during the northeast monsoon season develop as a complete reversal of the southwest monsoon pattern, facilitating low-level air flow from the north towards the Indian Ocean.

Associated northeasterlies traversing the Bay of Bengal and entering the southeast peninsular coast India and neighbouring Sri Lanka give rise to copious winter rains.

The southwesterlies across the peninsula are on the ebb in what is now a transition phase to the northeast monsoon. Helpful northerly flows are discernible but their easterly component has not evolved to the desired pattern.

These flows have to strengthen to set up the northeast monsoon onset. This requires a 'booster' circulation in the Bay of Bengal helping the flows to converge and be redirected towards Sri Lanka and the southeast coast of India.

Between 1901 and 2000, the onset of easterly winds took place between September 23 and November 1. The normal date for this change in wind direction was October 15.

During the same period of 100 years, the onset happened between October 4 and November 11, with the median normal being October 20.

WESTERN DISTURBANCE

International models have been predicting the formation of a Bay circulation during the course of the week but it would have to contend with opposite flows generated by an approaching western disturbance.

No big traction in the Bay is being forecast for the moment until October 20, though the US Naval Fleet Numerical Meteorology and Oceanography sees south China, the South China Sea and Indo-China progressively being brought under seasonal rains from the weekend.

What the nearly contiguous Bay of Bengal would need is a trigger mechanism in the form of a cyclonic circulation. The US Naval forecaster, however, sees some rain being dropped over Sri Lanka and along the southwest coast during this phase.

According to the US National Centres for Environmental Prediction (NCEP), the peninsular showers presumably sustained by residual southwest flows, may sustain until October 20.

Sri Lanka and the southeast coast are forecast to get rains sourced to what are identified as purely easterly flows only after October 20, the NCEP said.

Abnormal warming of the equatorial and east Pacific associated with an El Nino, the like of which is active concurrently, has been known to trigger the failure of the southwest monsoon.

But studies show that an El Nino may have the opposite effect on the northeast monsoon and may bring in reasonably good rain.

Here's the south-west monsoon withdrawal map .. http://yfrog.com/5nqaeg

Ominous Cloud Formation Has Russians Fearing An Alien Attack .. http://ping.fm/icnvV

Forecast: Clear Diwali day for Chennai

Recent weather patterns is like end of September.. "Clear morning, Mid morning low cloud formation from east, isolated showers around 1pm and clear sky after that."

This kind of weather will continue atleast till 20-Oct-09.

Here's the latest GFS for Diwali day, suggests a CLEAR day on Diwali!!

Today also South tamilnadu is active and we can see East-Bay is active also.

Latest satellite shows .. scattered thunder cells all along south-west coast.. remnant of SW monsoon. http://yfrog.com/1y61kj

Forecast: Clear Diwali day for Chennai

Recent weather patterns is like end of September.. "Clear morning, Mid morning low cloud formation from east, isolated showers around 1pm and clear sky after that."

This kind of weather will continue atleast till 20-Oct-09.

Here's the latest GFS for Diwali day, suggests a CLEAR day on Diwali!!

Monsoon withdrawal process gathers momentum

Withdrawal of southwest monsoon seemed to have acquired a sense of urgency with more areas emerging out of its influence on Monday.

This has reduced humidity levels but caused day temperatures to rise over many parts of northwest, east and central India.

An India Meteorological Department (IMD) update said that the monsoon has withdrawn from Uttarakhand, Uttar Pradesh, Rajasthan, Gujarat, entire Madhya Pradesh and many parts of Bihar, Jharkhand, Chhattisgarh and Maharashtra.

WITHDRAWAL LINE

The withdrawal line passed through Forbesganj, Ranchi, Raigarh, Yeotmal, Ahmednagar and Alibag on Monday.

Conditions are favourable for further withdrawal from the remaining parts of east and northeast India during the next three days.

A short-term outlook for October 15 to 17 said that the weather is likely to be mainly dry over most parts of the country outside south peninsular India where isolated to scattered rain or thundershowers is likely during the next four days.

The IMD expected no heavy rainfall at any part of the country during the next five days.

The maximum and minimum temperatures are likely to fall gradually by about 2 degrees Celsius during the next five days.

Satellite imagery on Monday showed convective clouds over parts of southeast Bay of Bengal and the Andaman Sea.

These seas are predicted to be in a state of flux through the course of the week, according to international models.

THUNDERSHOWERS

The Chennai Met Centre said in its update that rainfall occurred at a few places over interior Karnataka during the 24 hours ending Monday morning. Isolated rainfall occurred over Tamil Nadu, Andhra Pradesh, Kerala and coastal Karnataka.

Forecast for the next two days said that rain or thundershowers are likely at a few places over Tamil Nadu, Puducherry and Kerala.

Isolated rain or thundershowers have been forecast over Karnataka, Lakshadweep and Andhra Pradesh.

The European Centre for Medium-Range Weather Forecasts (ECMWF) maintained the outlook for the nearly contiguous water bodies of west Pacific/South China Sea/Bay of Bengal to rhyme in unison beyond October 15 precipitating onset of northeast monsoon (winter or reverse monsoon).

The trough encompassing these seas held into place on Monday mostly by a re-energised tropical storm Parma is expected to hold as such even after Parma weakens after an expected landfall over south China.

In fact, international models showed at least two fresh areas of convergence to the southeast of the Philippines on Monday, one of which would go on to become another typhoon-in-the-making, the ECMWF outlook suggested.

This likely typhoon is predicted to make an eventful landfall over the Philippines around October 22 according to the ECMWF outlook available on Monday.

After weakening, the westward-tracking typhoon would still likely have a ripple effect on the Bay of Bengal downstream.

India's Floods Reveal Climate Change Specter

Indian farmers had been praying for rain after the weakest monsoon season in 40 years had left their crops stricken by drought. But when the rains finally came, forceful and incessant at six times their normal levels, they left behind the worst floods southern India had seen in more than a century.

Weather officials blamed the heavy rains in Karnataka and Andhra Pradesh on a low-pressure system over the Bay of Bengal. So far, over 250 people have died in flooding made worse when officials were forced to open dams for fear they might burst. Some 1,500 relief camps have been set up for the estimated 2.5 million people who were displaced as the raging water destroyed entire villages, washing away roads, bridges, crops and livestock. (See pictures of India's 2008 floods.)

Although flooding has recently become commonplace in India - in 2008, over 3 million people were displaced when the Kosi river in Bihar burst its banks - but this year's deluge came as a shock because if followed a protracted drought, and a monsoon season branded a dud by the authorities. To experts who've tracked the effects of climate change, however, the flooding came as no surprise. In its fourth assessment report in 2007, the Inter- Government Panel on Climate Change (IPCC) predicted that more extreme droughts, floods, and storms, would become commonplace in the future, and that these intense weather conditions would follow in close succession to each other, often in the same areas.

The volatile weather patterns predicted by the IPCC are already beginning to show in India. The Doni river, a 93-mile stretch of water in north Karnataka has come to be known as "the Yellow River of Bijapur," after China's Hwang Ho. While the Chinese river is infamous for its sudden changes in course, the Indian version, whose water many consider no longer fit for human consumption, is gaining notoriety for its unpredictable nature - flash floods one day, barely a trickle the next. "We need to find a way of storing the excess water and using it through the rest of the year," says A.K. Bajaj, Chairman of India's Central Water Commission. (Read "India's Floods: a Manmade Disaster?")

The IPCC's predictions are grim for a country that still hasn't figured out an effective strategy for water management. In the northwest alone, the water table is falling by about 1.6 inches per year, according to the GRACE (Gravity Recovery and Climate Experiment) mission. At least half of India's precipitation comes from the annual monsoon rains, and as they become increasingly diminished and unpredictable, the country faces an imminent threat of extreme water shortages. Changing rainfall patterns aren't the only climate- change effect threatening India's water supply: Himalayan glaciers - the source for the many Indian rivers such as the Ganges - are melting at a rapid rate as a result of warmer temperatures. (See TIME's photo-essay "Worst Floods in 50 Years Hit Manila.)

Meager monsoons mean meager crops, and meager income, for Indian farmers. This year alone, the loss to crop yields and property in the two states has totaled almost $7 million. Dr. William Cline, a senior fellow at the Center for Global Development (CGD) and the Peterson Institute for International Economics says that of all the potential damage that could occur from climate change, damage to agriculture is likely to be the most devastating. "In the southern parts of India, damage will be substantial and similar to that in other countries also located close to the equator," he says. "In these locations, where temperatures are already at high levels, an increase in temperature will surpass crop tolerance levels."

Already, food shortages have become a major concern for the government, as the retail prices of vegetables shoot up. Damage to the onion crop in the recent floods, for example, saw the vegetable's price double within days.

Even without factoring in climate change, India's got a plate full of problems to deal with. Officials say ineffective management, bureaucracy and disaster planning have all contributed to the worsening of an already bad situation.

Just How Sensitive Is Earth's Climate to Atmospheric Carbon Dioxide?

Carbon dioxide levels climbing toward a doubling of the 280 parts per million (ppm) concentration found in the preindustrial atmosphere pose the question: What impact will this increased greenhouse gas load have on the climate? If relatively small changes in CO₂ levels have big effects-meaning that we live in a more sensitive climate system-the planet could warm by as much as 6 degrees Celsius on average with attendant results such as changed weather patterns and sea-level rise. A less sensitive climate system would mean average warming of less than 2 degrees C and, therefore, fewer ramifications from global warming.

Human civilization is now running an experiment (and without a control) that will definitively determine the answer. Scientists, however, have also realized that history can be a guide: Two new papers published in Science this week examine the historical record preserved in a stalagmite and microscopic seashells, respectively, to offer some clues.

Earth scientist Aradhna Tripati of the University of California, Los Angeles's Department of Earth and Space Sciences and her colleagues extracted a record of past atmospheric concentrations of CO₂ stretching back 20 million years from the shells of tiny creatures known as foraminifera buried in a column of ocean mud and rock. The microscopic animals build shells of calcium carbonate out of minerals in seawater-a process that is affected by the water's relative pH (acidity), which is, in turn controlled by the level of CO₂ in the atmosphere. More CO₂ in the atmosphere means a more acidic ocean.

"The two species we picked to analyze [Globigerinoides ruber and G. sacculifer] are both ones that are around today, and the living animals actually have photosynthetic algae as symbionts, which means that they live in the surface ocean, since the algae require sunlight to survive," Tripati explains. And that means the fossil record of their shells will reveal the relative acidity of the surface waters in the ratio of boron to calcium as well as the specific chemical signature of the boron itself. "When seawater is more acidic, less boron gets incorporated into the calcium carbonate shells," she adds.

The researchers first matched this fossil record secured by the Integrated Ocean Drilling Program Expedition in the western tropical Pacific to existing records from bubbles trapped in Antarctic ice cores that stretch back 800,000 years, which preserve a precise record of past atmospheric composition. Thus reassured of the technique's accuracy, they plunged back into deep geologic time.

"Modern-day levels of carbon dioxide were last reached about 15 million years ago," Tripati says, when sea levels were at least 25 meters higher and temperatures were at least 3 degrees C warmer on average. "During the middle Miocene, an [epoch] in Earth's history when carbon dioxide levels were sustained at values similar to what they are today [330 to 500 ppm], the planet was much warmer, sea level was higher, there was substantially less ice at the poles, and the distribution of rainfall was very different."

Further, "at no time in the last 20 million years have levels of carbon dioxide increased as rapidly as at present," Tripati adds; CO₂ concentrations have climbed from 280 ppm to 387 ppm in the past 200 years. And "our work indicates that moderate changes in carbon dioxide levels of 100 to 200 parts per million were associated with major climate transitions and large changes in temperature"-indicative of a very sensitive climate.

A nearly 400,000-year record of Ice Age transitions preserved in a stalagmite in the Sanbao and Linzhu caves of Hubei Province in China would seem to offer evidence in support of the sensitive climate scenario. The stalagmites, composed of calcium carbonate leached from dripping water, preserve a record of monsoon rainfall in the region by their composition. Paleoclimatologist Hai Cheng of the University of Minnesota and his colleagues then compared this record with climatic transitions, such as the shift into and out of an Ice Age.

The rock record reveals that such rainfall changes occur at the same time as general alterations in the relative strength of sunlight hitting the planet thanks to periodic shifts in Earth's orbit, known as Milankovitch cycles. At the same time as the solar heat increases, according to the monsoon record published in Science, CO₂ levels also begin to rise.

"Climate systems are well linked worldwide, such as sea-level, CO₂, ice sheet[s], the Asian monsoon, regional temperature and precipitation," Cheng says. "So a change in one of them could trigger changes in others." And that might mean the climate is too sensitive to tolerate current levels of CO₂ without changing the conditions that have allowed human civilization to flourish in the past 10,000 years.