We think it's cold here!

I’ve spent this week in Phoenix, Arizona, at the American Meteorological Society Annual Meeting. This meeting is an important one for us, as each year we hold our exhibition promoting our scientific journals, we meet many of our international members at our evening reception and we have our bilateral meeting with the AMS executive team to discuss areas of possible collaboration. And its good to renew old friendships.

We often joke about the weather with our US colleagues as we regularly have very extreme unseasonal weather for the AMS meetings. However we seem to have broken the trend this year. Phoenix itself is used to extreme weather conditions. Average summer temperatures are amongst the hottest in the US. On 26 June 1990 they reached an all-time high of 50°C (some 122°F). Rainfall is pretty sparse but there is a period between July to September where humidity levels are high.

This time of year is seasonally the coldest in Phoenix, with temperatures falling between a maximum of 19°C (67°F) and a minimum of 7°C (45°F). This week it has been up in the high end of the climatology - about 16°C (61°F) with sunny blue skies, as a result of a large high pressure sitting over the lower south west past of the US. To the north, much of the rest of the US has been experiencing some pretty cold weather with heavy snowfalls and some of the coldest parts experiencing temperatures around -42°C (-45°F), which is pretty chilly in anyone’s book.

But it wasn’t just the weather that made this year’s meeting a particularly special one. It was that 23 of the world’s meteorological Societies (the largest ever gathering) met to establish an International Forum for Meteorological Societies, where we can discuss issues of common interest and share best practice. The framework for the new forum was put in place and its first meeting will be in January 2010 at the AMS’s next annual meeting in Atlanta in January 2010.

As usual I managed to get hold of some upper atmosphere data from the Phoenix flight, through the in cabin screen displays that show altitude and temperature. Unfortunately I only got hold of some low level temperatures from the cabin display going into Phoenix. Coming out of Phoenix I managed to get some better data.

Surface temperature was pretty much the same on both days, but it was warmer in the upper air by some 5 to 6°C consistently up through at least the first 2.5 km. What’s interesting in the data from the 15th is the drop in temperature in the lowest 500 m or so showing a cold layer of low level air around the airport – I haven’t really looked into the properly, but possibly some cold air drainage from the surrounding mountains.

Weather Records and Average Temperatures

I was reading over the Christmas holidays that there are records of the weather that go back as far as 13th Century BC. The records were found amongst the Anyang oracle bones, which give us an historical account of the Shang dynasty in China. But it’s the way in which nature responds to our weather that gives us the long record that we use for studying our climate beyond the more systematic observations we have over the last century or so – the sorts of information that comes from tree rings or trapped air in ice cores, and that is what we call paleoclimatology. It’s these observations together with our complex climate models that help us to understand and give context to how our climate is changing.

Our recent summers haven’t been great in the UK, most likely a response to the effects of a strong La Niña – a large pool of cold water of the south-American coast. This natural feature of the earth’s climate has masked the underlying warming of land temperatures to some extend. That being said the climate models are telling us that by all accounts 2009 is set to be a warm year globally, although the seasonal forecasts for the UK are showing that we will have a cold start – with colder than average temperatures in January and an average February.

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.

Mountain Meteorology in Action

I was lamenting on what a bad decision it was not to take my new watch (re Blog of 12th October 2008) on my recent trip to Peru and the chance I would have had to give it a good test out in the Andes and to take a meteorological observation in Machu Picchu (what a fantastic place to visit by the way – twice as good as any photos you might have seen).

Fortunately the plane I travelled in was an Airbus with one of those screens that gives you temperature at different altitudes, so on take-off and landing I had the chance to record some upper air observations, and here are a couple below relating to my landing and then take-off at Lima airport:



You can see that they certainly do not conform to the ‘standard atmosphere’ (as defined by the International Civil Aviation Authority) of temperature changing by around 6°C per kilometre. Coming into Lima (blue line) you can see a warm layer of air just below 2 km that extends right down to about 700 m.

The flight from Lima into Cusco was an example of some of the challenges that aircraft have at high altitude. The landing is very spectacular as the plane circles around the mountains and comes into land in a shallow valley at around 3,600 m. You can hear the engines at high revs in the closing turns to maintain the lift they need to turn in the much thinner air (lower air pressure).

I was hoping to see some of my favourite lenticular clouds in the mountains, but not this time. However I did see some amazing cloud formations. Here is one example below; along with a picture I took at sunrise coming through the clouds as I travelled out of Cusco on a train to Machu Picchu.

My New Meteorological Watch

With one thing and another it has been a while since I last put ‘finger-to-keyboard’ so to speak, but felt I should share a few thoughts about my new meteorological watch.

At my age it is not often I get excited about my birthday (perhaps that is just because I am a bit miserable, as my wife reminds me), but this year I had a very exciting present – no not a vintage Harley Davidson bike, an antique Les Paul guitar, or tickets to see Catherine Jenkins in concert (front row seats); it was a meteorological watch. Yes, you did read correctly a watch that makes observations of the weather. I have had much fun with this, making observations of temperature pressure and altitude. It reminded me of a few things apart from how hopeless I am at finding out how it all works.

The first was how careful you have to be when making observations, to understand what is being observed (like the temperature of the atmosphere, or my wrist), and that the observations are well calibrated. I am waiting to my next blue sky day at the coast to set my altitude and pressure calibrations.

The second was that what I am measuring is all inter-related. Pressure, temperature and humidity are all related. For example in the troposphere, a very small layer of the earths atmosphere relatively speaking that is closest to the surface of the earth and where we have all of our weather, pressure decreases with height in the atmosphere and so does temperature, by roughly 6oC per kilometre (if we make some assumptions about what we call a standard atmosphere). I wonder whether my watch really does measure temperature, pressure and altitude independently or whether, as I suspect, it uses some of our understanding of how these things are linked.