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A breakthrough in long range forecasting?

Paul Hudson | 16:10 UK time, Monday, 22 March 2010

I am indebted to Dr Jarl Ahlbeck, from Abo Akademi University, Finland, who contacted me about his fascinating new piece of research relating to this winters severe cold across much of Europe, and a possible link to the very low solar activity we have been experiencing.

I am aware that there is a hugely varied readership of my blog; those who are very well informed about weather and climate, and others that have an interest in the subject but would struggle with some of the details contained in scientific papers. I have thus asked the author to summarize the main points of the research, and will include a link to the paper for those that feel brave enough to look into it themselves.

Dr Ahlbeck writes:

"Historically, low solar activity periods like the Dalton and Maunder Minima have been connected to cold winters in Europe. It seems very possible that the low solar activity forced areas of low pressures into a southern route or caused a negative Arctic Oscillation, AO, which in turn allowed cold air from the North Pole to flow across Europe. But can we obtain from real measurements that low solar activity really is able to do that?

I found that the mechanism is statistically significant, but it is not very simple to prove. There is no direct statistical relationship saying that low solar activity always should cause a negative Arctic Oscillation (which caused cold air to push further south than normal). But if we consider a second natural parameter, the strength and direction of the stratospheric wind in the Tropics (the Quasi-Biennial Oscillation index, QBO) I found a very interesting result: During periods of low solar activity (few or no sunspots) an easterly QBO causes a negative AO, but a westerly QBO causes a positive AO.

However, during low solar activity the easterly QBO causes a considerably stronger negative AO than the westerly QBO is able to cause a positive AO. Furthermore, easterly QBO is more common than westerly QBO during the Nordic Hemisphere winter.

The conclusion of my work is clear. If the sun goes into a new Dalton and Maunder minimum, we can therefore expect extremely cold winters in North America, Europe and Russia - which is exactly what was experienced during both the Maunder minimum (1600's) and the Dalton minimum (early 1800's)."


In essence what this research shows is that there is a link between the level of solar activity, the stratosphere, and the weather patterns that we experience, and gives more weight to the idea that solar effects may influence our weather (and hence climate) more than is currently accepted or understood.

There are Intriguing possibilities from a long range forecasting point of view. As the QBO is periodic, it's relatively straightforward to forecast for one to two years ahead. We can also usually determine where we are likely to be in the solar cycle for the following season and so the findings of this research could mean that severe winters like the one we have just experienced may be easier to forecast, months in advance.

Professor Stephen Mobbs at the National Centre for Atmospheric Science, commenting on the research told me:

"The stratosphere is very different to the part of the atmosphere we live in. There is a sharp divide at 8-15 km altitude between the troposphere where the weather occurs and the very stable and quiet stratosphere above. Our familiar weather is dominated by turbulent winds, clouds and transport of heat by convection plus phase changes of water from vapour to liquid to ice and vice versa.

By contrast, the stratosphere has smooth winds, virtually no clouds and only small (but very important) amounts of water vapour. Here, radiation dominates the transport of heat. Nevertheless, there is a growing body of evidence for some downward effect of the stratosphere on the troposphere and its weather systems. A curious phenomenon is the Quasi-Biennial Oscillation (QBO) in which the stratospheric winds change from easterlies to westerlies and vice versa, returning to their original state every 25-29 months. In spite of the name, the QBO has nothing to do with the length of the year - it is driven by atmospheric waves propagating up from the lower atmosphere. These waves are caused by mountains, land-sea heat contrasts, tropical convection and weather systems.

The QBO has proved difficult to reproduce in climate models and it is only in recent years that models such as the Met Office climate model have succeeded in doing this. There is now growing evidence that the QBO affects things like hurricane seasons, the monsoon and El Niño.

Since the heat transport in the stratosphere is dominated by radiation, it is quite plausible that solar radiation fluctuations could affect the stratospheric winds and hence the waves which drive the QBO."

You can read Dr Ahlbeck's research paper in PDF format by clicking here [214KB PDF]


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