The harsh winter in America was caused by a rare coincidence of weather events, say scientists

Scientists have shown that a severe snowfall in North America and Northern Europe in the winter of 2009-2010 was caused by a rare, once in a century, collision of two weather systems.

They concluded the harsh winter and heavy snow was an example of hard to predict weather events, not a change in climate.

They analysed historical snow records.

The research was published in Geophysical Research Letters.

In the winter of 2009-2010 much of Northern Europe experienced heavy snow and temperatures were at the lowest they had been for nearly 30 years. At the same time, record snowfall hit Washington DC and other parts of America’s “Mid-Atlantic states”.

Some news reports took the extreme cold weather as evidence against climate change.

By analysing 60 years of snowfall measurements and satellite data, researchers concluded the anomalous weather conditions were caused by an unusual combination of an El Nino event and the rare occurrence of a strongly negative North Atlantic Oscillation (NAO).

El Nino events result from a periodic warming of the tropical Pacific Ocean coupled with changes in the atmosphere. El Ninos move storm systems in the Northern Hemisphere towards the equator. They occur every few years and can be predicted up to a few seasons in advance.

The North Atlantic Oscillation (NAO) is climatic phenomenon resulting from shifts in atmospheric pressure between two regions above the North Atlantic Ocean. Large changes can only be forecast a week or two weeks in advance.

When the NAO enters a strongly negative phase, cold air repeatedly comes down from the Arctic. This affects eastern North America, and Western Europe.

Snow that covered most of the UK was caused by a rare weather system bringing down cold air from the Arctic

Richard Seager, a meteorologist with the Lamont Doherty Earth Observatory at Columbia University, US, is one of the lead authors of the paper.

“The NAO was probably as negative as it’s ever been in the instrumental record, which goes back to the early 1800s. This was a once in a century type of event,” he told BBC News.

It was this combined with the El Nino event that caused the severe snowfall in North America.

“The NAO on its own doesn’t cause much precipitation in America. It just makes it cold. The El Nino makes the US wetter than normal so combined with the NAO it caused the precipitation in America to fall as snow,” he told BBC News.

The researchers also believe it is unlikely this combination will occur in the near future. Data from tree rings have shown that these same conditions caused by the same combination of weather systems happened over 200 years ago in the winter of 1783 – 1784 in Northern Europe and North America.

Many people have concluded the extreme winter in 1783/84 was caused by the eruption of an Icelandic volcano. But the researchers believe it was caused by the same combination of weather events that caused last year’s harsh winter.

Richard Seager also believes the research is a counter to suggestions that the cold winter is evidence against climate change.

“Weather will continue to be weather. You have to average over a lot of weather to get the climate trends. There doesn’t seem to be any need to evoke anything else other than that,” he told BBC News

http://www.bbc.co.uk/news/science-environment-11152077

Evacuations have begun in areas of the US East Coast likely to be hit by Hurricane Earl.

The hurricane has strengthened to a category four storm again, generating sustained winds of 215km/h (135mph).

President Barack Obama said officials needed to be ready for a “worst case” scenario in a call to the US Federal Emergency Management Agency (Fema).

North Carolina’s Governor Beth Perdue has declared a state of emergency.

US officials have ordered a mandatory evacuation for thousands of visitors and residents on Ocracoke Island and Hatteras Island.

Both islands are part of North Carolina’s Outer Banks, a region popular with tourists.

Fema has warned people along much of the the Eastern Seaboard of the US to be vigilant and follow official bulletins.

Forecasters at the National Hurricane Center said they expected the hurricane to turn north and then run parallel to the East Coast.

They temporarily downgraded Earl to a category three storm on Wednesday, but the hurricane strengthened to a category four again later in the day.

“The most important thing for people living in Earl’s potential tract to do is to listen to and follow the instructions of their local officials,” Fema administrator Craig Fugate said.

A hurricane warning has been issued for the east coast of the US from Bogue Inlet, North Carolina north-eastward to the North Carolina/Virginia border, including the Pamlico and Albemarle sounds.

The hurricane watch has been adjusted northward and now extends from the North Carolina/Virginia border northward to Massachusetts, including Martha’s Vineyard and Nantucket.

A warning means hurricane conditions are expected somewhere within the affected area, with the first tropical storm-force winds within 36 hours. A watch expects the same within 48 hours.

The local authorities in the Outer Banks expect the storm to pass 80 miles (130km) away from the islands, meaning high winds and waves are likely.

The hurricane is currently east of the central Bahamas and is moving north-west.

On Monday the hurricane battered north-eastern Caribbean islands and Puerto Rico, causing power cuts and flooding.

Earl is being followed by Tropical Storm Fiona, currently moving north of the Leeward Isles, and Tropical Storm Gaston, the fourth tropical storm to have formed in the last 11 days.

http://www.bbc.co.uk/news/world-us-canada-11154296

A storm moving through the eastern Caribbean has strengthened to a Category Four hurricane, prompting warnings for several islands.

Hurricane Earl is expected to gain more strength before heading towards the US.

Forecasters say it is a major hurricane and could cause “catastrophic” damage if it hits land.

Strong winds and heavy rains are already lashing several islands in Caribbean, but the storm has now passed by the Virgin Islands.

The hurricane is generating sustained winds of 215km/h (135mph).

It is currently north-east of Puerto Rico, and moving west-northwest at about 24km/h, the US-based National Hurricane Center (NHC) reports.

The centre of the storm is expected to move away from the Virgin Islands on Monday night and pass to the east of the Turks and Caicos on Tuesday night.

Hurricane warnings in place on several islands in the region have now been degraded.

However, Earl caused heavy rains and flooding in low-lying areas, and it damaged homes on several islands including Antigua and Barbuda.

Several countries reported power outages. Cruise ships were diverted and flights cancelled across the region.

The NHC said it was too early to say what effect Earl would have on the eastern US coast later in the week, but it warned coastal residents from North Carolina to Maine to watch the storm’s path.

Earl is being closely followed by Tropical Storm Fiona, currently east of the Leeward Isles with winds of up to 65km/h.

http://www.bbc.co.uk/news/world-latin-america-11128738

The Sun's conveyor transports plasma across its surface to the pole, where it sinks before rising at the equator

Solar physicists may have discovered why the Sun recently experienced a prolonged period of weak activity.

The most recent so-called “solar minimum” occurred in December 2008.

Its drawn-out nature extended the total length of the last solar cycle – the repeating cycle of the Sun’s activity – to 12.6 years, making it the longest in almost 200 years.

During a solar minimum the Sun is less active, producing fewer sunspots and flares.

The new research suggests that the longer-than-expected period of weak activity may have been linked to changes in the way a hot soup of charged particles called plasma circulated in the Sun.

The study, conducted by Dr Mausumi Dikpati of the National Center for Atmospheric Research in Colorado and her US colleagues, is published in the journal Geophysical Research Letters.

The Sun’s activity strengthens and weakens on a cycle that typically lasts 10.7 years. Since accurate records began in 1755, there have been 24 such solar cycles.

The 23rd cycle, which ended in December 2008, was both longer than average and had the smallest number of sunspots for a century. Sunspots are areas of intense magnetic activity that are visible as dark spots on the star’s surface.

Currents of fire

The new research suggests that one reason for the prolonged period of weak activity could be changes in the Sun’s “conveyor belt”.

Similar to the Earth’s ocean currents, the Sun’s conveyor transports plasma across its surface to the pole. Here, the plasma sinks into the heart of the Sun before rising again at the equator.

During the 23rd cycle, these currents of fire extended all the way to the poles, while in earlier cycles they only extended about two thirds of the way.

Dr Roger Ulrich of the University of California, Los Angeles, a co-author of the study, said the findings highlighted the importance of our monitoring of the Sun.

The research team used sophisticated computer simulations to show how changes in the conveyor might have affected cycle duration. They found that the increased length of the conveyor and its slower rate of return flow explained the prolonged 23rd cycle.

However, Dr David Hathaway, a solar physicist from Nasa’s Marshall Space Flight Center in Alabama, who was not involved in the latest study, argued that it was the speed and not the extent of the conveyor that was of real importance.

The conveyor has been running at record high-speeds for over five years. Dr Hathaway said: “I believe this could explain the unusually deep solar minimum.”

http://www.bbc.co.uk/news/science-environment-10967292

The Asian monsoon has brought unusually high levels of rain to the region, with catastrophic consequences in countries from Pakistan and India to North Korea and China.

Nasa has used satellite images from 1 to 9 August to show the intensity of rainfall compared to average rates for the same period in previous years.

The darker blue shows where rain was much more intense than usual; brown indicates less intense rainfall. Some regions have had as much as 24 millimetres of rain per day above normal.

In Khanpur, in Pakistan’s Sindh district, for example, the average rainfall is 17.4mm for the whole month of August. So far, 255mm has fallen in 12 days.

The annual monsoon season, typically from June to September, is caused by the difference in temperature between the land and the sea.

As the Tibetan plateau warms up, heated air rises, drawing in moist air from the sea to replace it. This also warms, rises and the water condenses into rain.

The BBC Weather Centre says a kink in the jet stream of fast-moving air in the upper atmosphere has exacerbated conditions this year. More spiralling air in the upper atmosphere sucks in more moist air, causing larger clouds and more intense rainfall.

http://www.bbc.co.uk/news/world-south-asia-10951517

Flash floods brought on by rains in central Europe and the Baltic have killed at least 15, officials say.

Rivers overflowed their banks, sending torrents of water through Bogatynia in south-west Poland and Goerlitz in eastern Germany.

The Neisse river, on the border with Poland, reached its highest recorded level in Goerlitz.

Three Poles, three Germans and five Czechs were killed, while further north in Lithuania four people were killed.

Three other Czechs were reported missing after the downpours on Saturday triggered the floods.

The army, police and fire services were using helicopters and boats to move people away from the flood zones and clear flood debris.

‘No time’

The heavy downpour caused Poland’s Miedzianka river to overflow, flooding Bogatynia before swelling the Niesse river.

One woman drowned in Bogatynia while a 55-year-old firefighter was swept away when a dyke burst its banks.

Another woman drowned in the nearby town of Zgorzelec, across the Niesse from Goerlitz.

The Neisse reached its highest recorded level of 7.07 metres (23 feet).

“The flood wave hit the town in a few hours. We couldn’t do anything to get ready for that,” the mayor of Goerlitz, Michael Wieler, told German TV.

Police said 1,500 people evacuated their homes in Goerlitz as torrents of water rushed through the streets.

Further west, near Chemnitz, three Germans were found drowned in the flooded cellar of the building they lived in in Neukirchen, near the Czech border.

Police said they had been trying to carry furniture upstairs.

An additional five people drowned over the weekend in the Czech Republic where people were plucked by helicopter from the roofs of their homes in the towns of Chrastava and Frydlant.

As the storms moved north, four people were killed in Lithuania. Two campers died when a tree collapsed on their tent, local media reported.

The same region was hit by heavy flooding in May and June this year, killing nearly 30 people.

Poland’s Prime Minister Donald Tusk has promised emergency aid payouts to help people affected by the floods.

http://www.bbc.co.uk/news/world-europe-10909818