antwoord op 'Hoe' (Zie onderzoek Lockwood, link)
Bericht van: sebastiaan (bussum) , 02-03-2011 20:11
http://news.bbc.co.uk/2/hi/8615789.stm
Dat onderzoek geeft ook aan dat vermindering vd zonneactiviteit met name voor West Europa gevolgen heeft.
Big chill
Professor Lockwood said that there were a number of possibilities that could explain the link, but the team favoured the idea of a meteorological phenomenon known as "blocking".
This affects the dynamics of jet streams, which are very strong winds about 7-12km above the Earth's surface that can have a major influence on weather systems. There is one jet stream present in each hemisphere.
Solar activity has been in decline since 1985, says Professor Lockwood
'No Sun link' to climate change
"Europe is particularly susceptible because, firstly, it lies underneath the (northern hemisphere's) jet stream," he explained.
A "blocking" occurs when the jet stream forms an "s" shape over the north-eastern Atlantic, causing the wind to fold back over itself.
"If you haven't got blocking, then the jet stream brings the mild, wet westerly winds to give us the weather we are famous for."
But, he added, if the jet stream is "blocked", and pushed further northwards, then cold, dry winds from the east flow over Europe, resulting in a sharp fall in temperatures.
"This... 'blocking' does seem to be one of the things that can be modulated by solar activity," he said.
Recent studies suggest that when solar activity is low, "blocking" events move eastwards from above north-eastern North America towards Europe, and become more stable.
A prolonged "blocking" during the most recent winter was responsible for the long spell of freezing conditions that gripped Europe.
Written observations from the period of the Maunder Minimum referred to the wind coming from the east during particularly cold winters, which strengthened the team's "blocking" hypothesis.
The way in which solar activity affects the behaviour of blocking episodes is linked to the amount of ultraviolet (UV) emissions being produced by the Sun.
Solar UV heats the stratosphere (20-50km above the surface), particularly the equatorial stratosphere. This results in a temperature gradient, which leads to the formation of high level winds.
"The change in solar activity undoubtedly changes the stratospheric winds," said Professor Lockwood.
Studies have shown that the state of the stratosphere can make a considerable difference to what happens in the troposphere, which is where the jet stream occurs, Professor Lockwood explained.
"There has been some quite simple modelling that indicated that heating the equatorial stratosphere with more UV would actually move the jet streams a little bit, by just a few degrees.
"That, of course, has the potential to change the behaviour of the jet streams - and that is the sort of thing that we think we are seeing."
'Blocking central'
Professor Lockwood was keen to stress that "blocking" only affected a limited geographical region, and would not have a widespread impact on the global climate system.
To illustrate the point, he said that while the CET record showed that this winter was the UK's 14th coldest in 160 years, global figures listed it as the fifth warmest.
He said that one of his colleagues at the University of Reading referred to Europe as "blocking central".
"Frost fayres" were held on the Thames during the Maunder Minimum
"The reason is largely because the jet stream has to come to us over the Atlantic Ocean and it is slowed down when it hits the land in Europe.
"You don't quite have the same combination of circumstances anywhere else in the world that gives you such strong blocking."
While the current decline in solar activity is expected to continue in the coming decades, he cautioned that more frequent "blocking" episodes would not result in Europe being plunged into sub-zero temperatures every winter.
"If we look at the last period of very low solar activity at the end of the 17th Century, we find the coldest winter on record in 1684, but the very next year - when solar activity was still low - saw third warmest winter in the entire 350-year (CET) record."
A number of other meteorological factors also influenced the weather systems over Europe, so a number of parameters had to be met before a "blocking" occurred, he observed.
Responding to the team's findings, Dr Peter Stott, head of climate monitoring and attribution at the UK Met Office, said: "This paper provides some additional evidence that what happens in the stratosphere could be important for climate at the surface."
But he added: "The findings are suggestive of a possible effect but more research is needed to pin down the mechanisms and determine how significant such effects could be for determining the probability of cold winters in the UK.
"At the Met Office, we are already working on research into incorporating better representation of the stratosphere into our seasonal and decadal forecasting models."
Dat onderzoek geeft ook aan dat vermindering vd zonneactiviteit met name voor West Europa gevolgen heeft.
Big chill
Professor Lockwood said that there were a number of possibilities that could explain the link, but the team favoured the idea of a meteorological phenomenon known as "blocking".
This affects the dynamics of jet streams, which are very strong winds about 7-12km above the Earth's surface that can have a major influence on weather systems. There is one jet stream present in each hemisphere.
Solar activity has been in decline since 1985, says Professor Lockwood
'No Sun link' to climate change
"Europe is particularly susceptible because, firstly, it lies underneath the (northern hemisphere's) jet stream," he explained.
A "blocking" occurs when the jet stream forms an "s" shape over the north-eastern Atlantic, causing the wind to fold back over itself.
"If you haven't got blocking, then the jet stream brings the mild, wet westerly winds to give us the weather we are famous for."
But, he added, if the jet stream is "blocked", and pushed further northwards, then cold, dry winds from the east flow over Europe, resulting in a sharp fall in temperatures.
"This... 'blocking' does seem to be one of the things that can be modulated by solar activity," he said.
Recent studies suggest that when solar activity is low, "blocking" events move eastwards from above north-eastern North America towards Europe, and become more stable.
A prolonged "blocking" during the most recent winter was responsible for the long spell of freezing conditions that gripped Europe.
Written observations from the period of the Maunder Minimum referred to the wind coming from the east during particularly cold winters, which strengthened the team's "blocking" hypothesis.
The way in which solar activity affects the behaviour of blocking episodes is linked to the amount of ultraviolet (UV) emissions being produced by the Sun.
Solar UV heats the stratosphere (20-50km above the surface), particularly the equatorial stratosphere. This results in a temperature gradient, which leads to the formation of high level winds.
"The change in solar activity undoubtedly changes the stratospheric winds," said Professor Lockwood.
Studies have shown that the state of the stratosphere can make a considerable difference to what happens in the troposphere, which is where the jet stream occurs, Professor Lockwood explained.
"There has been some quite simple modelling that indicated that heating the equatorial stratosphere with more UV would actually move the jet streams a little bit, by just a few degrees.
"That, of course, has the potential to change the behaviour of the jet streams - and that is the sort of thing that we think we are seeing."
'Blocking central'
Professor Lockwood was keen to stress that "blocking" only affected a limited geographical region, and would not have a widespread impact on the global climate system.
To illustrate the point, he said that while the CET record showed that this winter was the UK's 14th coldest in 160 years, global figures listed it as the fifth warmest.
He said that one of his colleagues at the University of Reading referred to Europe as "blocking central".
"Frost fayres" were held on the Thames during the Maunder Minimum
"The reason is largely because the jet stream has to come to us over the Atlantic Ocean and it is slowed down when it hits the land in Europe.
"You don't quite have the same combination of circumstances anywhere else in the world that gives you such strong blocking."
While the current decline in solar activity is expected to continue in the coming decades, he cautioned that more frequent "blocking" episodes would not result in Europe being plunged into sub-zero temperatures every winter.
"If we look at the last period of very low solar activity at the end of the 17th Century, we find the coldest winter on record in 1684, but the very next year - when solar activity was still low - saw third warmest winter in the entire 350-year (CET) record."
A number of other meteorological factors also influenced the weather systems over Europe, so a number of parameters had to be met before a "blocking" occurred, he observed.
Responding to the team's findings, Dr Peter Stott, head of climate monitoring and attribution at the UK Met Office, said: "This paper provides some additional evidence that what happens in the stratosphere could be important for climate at the surface."
But he added: "The findings are suggestive of a possible effect but more research is needed to pin down the mechanisms and determine how significant such effects could be for determining the probability of cold winters in the UK.
"At the Met Office, we are already working on research into incorporating better representation of the stratosphere into our seasonal and decadal forecasting models."
„Et nul ne se connait tant qu'il n'a pas souffert, „C'est une dure loi, mais une loi suprème, „Vieille comme le monde et la fatalité, „Qu'l nous faut du malheur regevoir le baptéme, ~Et qu'a ce triste prix tout doit étre acheté. „Les moissons pour murir out besoin de rosée, „Pour vivre et pour sentir l'homme a besoin de pleura, „La joie a pour symbole une plante brisée, „Humide encore de pluie et couverte de fleurs."
