Wednesday, 22 October 2008

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.

Sunday, 12 October 2008

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.