Very Cold December

It’s been the coldest start to December since 1976. Very cold Decembers are not uncommon but a little unusual as our coldest months in the UK are usually January and February. I was talking about the cold weather to some friends over Christmas and we got on to talking about why we can feel hot or cold. I don’t mean that the heating isn’t on or there’s a freezing wind outside, I mean where the sensation of heat actually comes from.

Well, something feels hot to us because the atoms inside it are moving fast, and when it feels cold they are moving slowly. We interpret this movement through the feeling of something being hot or cold, and a thermometer interprets as a certain temperature, in for example degrees Centigrade of Fahrenheit.

Scientists often use Kelvin as a measure of temperature rather than deg C or deg F. The bottom of the Kelvin scale is 0 K or Absolute Zero. What got me thinking about this recently was my God Son who asked me what is Absolute Zero. I was able to give the temperature 0 K or -273.15°C, but not the definition. It’s one of those things that I am sure I did know and could make a reasonable guess of what I thought it was, but to be precise I looked it up for myself. And it is as you might guess a point at which no more heat exists.

What that means specifically in classical kinetic theory is that there should be no movement of individual molecules at Absolute Zero. In practice we don’t of course know this as we have never been able to observe anything at 0 K, but we have come close in the laboratory. The experimental evidence shows us that as we reduce temperatures close to 0 K molecules do slow right down, but there is still movement.

It’s getting darker by the second

Watch a related video of Paul being interviewed on BBC Radio Berkshire



Well, we’ve had the longest day for 2008 and summer has officially begun, albeit a very windy start – the Yorkshire relatives had their plant pots blown away last week! On the radio slot this week we were talking about why we have seasons and of late it’s certainly felt like we’ve had all of these in a week or so (not quite as Crowded House sang about). It did remind me what interesting weather we have by virtue of being an island near a large ocean and continent in the mid-latitudes, and how lucky we are that we don’t have to battle the sort of severe weather that some parts of the world face this time of year.

Central Europe has been having some lively weather if the football coverage is anything to go by. But for a change, Glastonbury had a very sunny start. Tonight (Thursday) and Sunday might require the wellies to be unpacked, well at least the shower coat anyway. I noticed on Sunday that The Verve, Leonard Cohen, Neil Diamond and Gilbert O’Sullivan are playing – now there’s an eclectic music mix that sounds like the sort of thing you get when you put your iPod into Shuffle mode.

I’m a tennis fan so I’m hoping that we have some very seasonal summer weather for the next week of Wimbledon, but by all accounts it does look like we might be in for a shower or two on the middle Sunday and later in the second week. Let’s hope Andy Murray’s still out on the court braving the elements!

What is Wind?

It’s Father’s Day on Sunday (too late for a card now!), but the weekend is also the European Wind Energy weekend. I was asked one of those simple yet hard to explain questions like why is the sky blue (for a later week’s discussions) this week - why are there winds? Well, the answer I gave was very simply the air moves from points of high pressure to points of low pressure, which creates our wind – of course it’s a lot more complicated than simply describing what we call ‘the pressure gradient force’, but that’s basically why we have wind.

The air doesn’t always manage to move directly from High to Low pressure because it can be affected by the wider scale flow of our atmosphere (on the big scale) and local temperature differences (on a small scale), so like lots of things in meteorology we have effects going on at many levels or as we call it spatial scales.

Speaking of scales, and we like our measuring scales in meteorology, we have lots of ways of measuring winds. The most famous of course is the Beaufort Scale (named after its inventor Admiral Sir Francis Beaufort) which measures wind in a range 0 (clam) to 12 (hurricane force). For stronger winds, specifically for tornadoes, we have the Fujita scale after Ted Fujita (or more correctly now the Enhanced Fujita scale), which goes from EF1 to EF5 and relates to the scale of damage, and we have the Saffir-Simpson scale for Hurricanes, which goes from Category 1 to the most severe at Category 5.

One strong wind that has become more commonly talked about in a few recent TV documentaries is the Jet Stream (or more specifically the Polar Jet Stream). This is a very strong jet of air that travels at great speed high up in the atmosphere, in fact about 10km up (or for those of you not yet metric, that’s just over 6 miles up). This jet stream can often bring bad weather across the Atlantic to the UK, and last summer in particular when the jet was over the UK (instead of its more usual northerly summer position) we saw some pretty unseasonally wet and windy weather.

I once read that if we could harness just 1% of the power of the jet stream then we would have enough energy to power the world’s current energy needs – but 10km is a heck of a long power cable!