It's to do with nucleation sites. If you look at where bubbles form in a glass of beer, they always form on the edges or the surface of the glass and it's exactly the same way that a raindrop forms and it's exactly the same way as a bubble of air forms. You need to have something for it to form on. Bubbles usually start on little peaks and troughs on the surface of the glass. Avid listeners of the Naked Scientists will have a few weeks ago heard Professor Herbert Huppert doing an experiment where he put some sugar into a bottle of lemonade and lots of nucleation sites were formed and the bottle of lemonade exploded. In other words, a nucleation site is a rough area on a surface. If you look at water, the reason fish can breathe underwater is because the water is full of dissolved oxygen and other gases. If you have a rough patch on the side of something such as glass, that can act as a point where the gas molecules come together to form a bigger an bigger bubble. You can see this if you pour yourself a glass of tap water and leave it by the bed overnight. When you wake up in the morning, it will be all bubbly. Those bubbles will form wherever there is a rough patch on the side of the glass.

I think you do get a slight effect on it because you get more energy input when the sun's particularly active but it's a fairly routine and regularly forecast cycle. So we wouldn't use it hugely to impact on our daily weather forecast. If you're talking about longer term weather and you're starting to talk about climate then it's certainly the case that if you look at, for example, the last century then periods of strong solar activity were associated with periods of warmer temperatures. However, that influence in the latter part of the century was greatly outweighed by the effect of increasing levels of carbon dioxide. If you calculate the amount of energy that comes from the sun you get a little bit extra when the sun spots are very active. That does tend to make the weather a little bit more active but as for its actual impact on me as a weather forecaster, it's relatively small.

That's a very good questions actually because weather forecasts do go wrong and we've all seen that. We have a scientific basis for understanding that and it's a phenomenon called chaos theory. Things like the tides, for example, are very predictable. We can predict tides years or decades ahead. We can predict eclipses hundreds of years ahead. But these are not chaotic phenomena. The weather is a chaotic phenomena. What this means is that we can never when we go out to these time scales of years and months or seasons ahead, we can never make absolute definite predictions. What we make are what we call probabilistic predictions. What we will do is say that the chance of it being wetter than normal or warmer than normal would be maybe 80% or 90% depending on the confidence we have in the prediction and this will be useful information because obviously without that information all you could say is that there's a 50% chance of it being warmer than normal or colder than normal. So this is how we deal with chaos theory in the weather by going towards a more probabilistic prediction. But nevertheless, in many applications these turn out to be very useful types of forecast.

Friction basically. We have a theoretical wind speed which we call the geostrophic wind speed and that's just the speed you would have if there's no friction. But when the air that is moving is in contact with the ground, then you get friction. This takes a bit of energy out and makes the bottom of the atmosphere very turbulent. That's where you get the gusts from. It's this turbulence and mixing at the bottom that causes gusts.

In terms of the ocean affecting the weather, the ocean has a very strong influence on seasonal weather. If you're talking about needing weather predictions several months ahead, then you do very much need to look at the ocean temperatures. In fact, if we look at this last winter, it's been incredibly dry here in the UK. That's been closely connected to the fact that we've had incredibly warm sea temperatures in the tropical Atlantic. If we look back to the autumn we had lots of hurricane activity including the one in New Orleans, and that was also connected with sea surface temperatures. For European winters, you have one of two situations. You either have the case where you have a very strong jet stream that brings all the storms across the Atlantic to the UK. In those situations you'll typically have warm, wet winters. The other situation is where you have a much weaker jet stream and the storms tend to get deflected up north or down south. In those situations you typically have a cold, dry winter in the UK. Whether or not you're in one or the other situation is largely modulated by the sea surface temperatures are like in the Atlantic Ocean.

That's a 64 000 dollar question, that one! I'm not confident about this but it's probably to do with the amount of energy that's discharged from the bottom of the cloud. They'll be going through slightly different raindrops. The colour that you're seeing will also be dictated by the chemical behaviour of the things that get ionised or heated up by the lightning. So if there's contamination in the atmosphere, perhaps that could play a role. Street lights are orange because they contain sodium. If you heat sodium up to a very high level, the wavelength of light that you emit is an orange colour. Perhaps there are certain things in the air at that time that can affect the colour of the discharge.

It's all to do with chaos, which is what Tim was mentioning earlier. The weather is chaotic, so there are situations where it can be very unpredictable.