ScienceDaily (Apr. 19, 2010) — A link between low solar activity and jet streams over the Atlantic could explain why, despite global warming trends, people in regions North East of the Atlantic Ocean might need to brace themselves for more frequent cold winters in years to come.
A new report published on April 15, in IOP Publishing's Environmental Research Letters, describes how we are moving into an era of lower solar activity which is likely to result in UK winter temperatures more like those seen at the end of the seventeenth century.
Lead author Mike Lockwood of the University of Reading said: "This year's winter in the UK has been the 14th coldest in the last 160 years and yet the global average temperature for the same period has been the 5th highest. We have discovered that this kind of anomaly is significantly more common when solar activity is low."
The new paper, 'Are cold winters in Europe associated with low solar activity?', differs from previous efforts to explain the UK's recent cold winters by comparing the most comprehensive, but regionally specific, temperature dataset available (the Central England Temperature dataset) to the long-term behaviour of the Sun's magnetic field, and to trends across the entire Northern Hemisphere.
The paper is being published now as the researchers have just had the opportunity to put this year's data to the test and found that this year's results fit well with the trends they have discovered.
The researchers suggest that the anomaly in Northern Europe's winter temperatures could be to do with a phenomenon called 'blocking'.
'Blocking' is related to the jet stream which brings winds from the west, over the Atlantic, and into Northern Europe but, over the past couple of winters, could have lost its way, for weeks at a time, in an 'anticyclone' before it reaches Europe.
The researchers have found strong correlations between weak solar activity and the occurrences of 'blocking'. As the temperature is affected by a weak Sun so the wind's patterns also change and, as the warmer westerly winds fail to arrive, the UK is hit by north-easterlies from the Arctic.
The researchers, from the Department of Meteorology at the University of Reading, the Science and Technology Facilities Council Space Science and Technology Department, and the Max-Planck Institute for Solar System Research in Katlenburg-Lindau, Germany, are keen to stress the regional and seasonal (European and winter) nature of their research.
Professor Mike Lockwood has explained that the trends do not guarantee colder winters but they do suggest that colder winters will become more frequent. He said: "If we look at the last period of very low solar activity at the end of the seventeenth century, we find the coldest winter on record in 1684 but, for example, the very next year, when solar activity was still low, saw the third warmest winter in the entire 350-year record.
"The results do show however that there are a greater number of cold UK winters when solar activity is low."
Minggu, 16 Januari 2011
Link Between Solar Activity and the UK's Cold Winters
Dramatic Ocean Circulation Changes Caused a Colder Europe in the Past
ScienceDaily (Jan. 15, 2011) — The unusually cold weather this winter has been caused by a change in the winds. Instead of the typical westerly winds warmed by Atlantic surface ocean currents, cold northerly Arctic winds are influencing much of Europe.
However, scientists have long suspected that far more severe and longer-lasting cold intervals have been caused by changes to the circulation of the warm Atlantic ocean currents themselves.
Now new research led by Cardiff University, with scientists in the UK and US, reveals that these ocean circulation changes may have been more dramatic than previously thought.
The findings, published January 14, 2011 in the journal Science, show that as the last Ice Age came to an end (10,000 -- 20,000 years ago) the formation of deep water in the North-East Atlantic repeatedly switched on and off. This caused the climate to warm and cool for centuries at a time.
The circulation of the world's ocean helps to regulate the global climate. One way it does this is through the transport of heat carried by vast ocean currents, which together form the 'Great ocean conveyor'. Key to this conveyor is the sinking of water in the North-East Atlantic, a process that causes warm tropical waters to flow northwards in order to replace the sinking water. Europe is kept warmer by this circulation, so that a strong reduction in the rate at which deep water forms can cause widespread cooling of up to 10 degrees Celsius.
Lead author Dr David Thornalley, Cardiff School of Earth and Ocean Sciences, explains how the scientists studied changes in ocean circulation: "We retrieved ocean sediment cores from the seafloor of the Northeast Atlantic which contained the shells of small organisms. We used these shells to examine the past distribution of radiocarbon in the ocean. Radiocarbon is a radioactive form of carbon that acts like a natural stopwatch, timing how long it has been since water was last at the sea surface. This allows us to determine how quickly deep water was forming in the Northeast Atlantic at different times in the past."
The team of scientists found that each time deep water formation switched off, the Northeast Atlantic did not fill with water that sank locally. Instead it became inundated with water that had originally formed near Antarctica and then spread rapidly northwards. The new results suggest that the Atlantic ocean is capable of radical changes in how it circulates on timescales as short as a few decades.
Dr Thornalley said: "These insights highlight just how dynamic and sensitive ocean circulation can be. Whilst the circulation of the modern ocean is probably much more stable than it was at the end of the last Ice Age, and therefore much less likely to undergo such dramatic changes, it is important that we keep developing our understanding of the climate system and how it responds when given a push."
The research is funded through the Natural Environment Research Council's Rapid Climate Change programme and the National Science Foundation (USA). The Science paper The Deglacial Evolution of North Atlantic Deep
