Fingerprints of Weather

The weather in Manchester feels autumnal. There has been almost constant drizzle all week accompanied by driving wind and even some leaves falling from the trees. The weather has certainly not been conducive to astronomical observations and has made my daily cycle to work and back rather damp. I did catch a very brief glimpse of what I think was Jupiter a few nights ago but haven't seen much else since.

Thankfully clouds don't affect radio telescopes too much although water vapour in our atmosphere does emit (and absorb) electromagnetic radiation in the radio part of the spectrum. If the observing frequency gets high enough, or if there is enough water vapour, you'll start to get 'clouded out' on radio telescopes too. It is also possible to 'see' storms with a radio telescope because lightning tends to emit across the electromagnetic spectrum.

Radio telescope voltages
Raw voltage levels from three radio telescopes that are part of MERLIN in the UK. CREDIT: Stuart/Jodrell Bank Centre for Astrophysics
I created a quick and dirty visualisation of some of the effects of today's weather on the raw output from three radio telescopes operated by Jodrell Bank Centre for Astrophysics. Each of the three horizontal strips represent an hour or so of readings for a particular telescope. In each case, red represents 'brighter' radio emission and blue 'fainter' emission (you can also think of it as hot and cold) but note that the scale is different for each telescope. Sudden increases in emission - spikes - can be seen as narrow bands of colour (mostly orange or red).

The top telescope in my plot is based near Cambridge and was parked i.e. it was pointing upwards and not looking at anything in particular. Whilst the banding may just be an over amplification of noise, the weather forecast has shown the Cambridge area under a heavy band of rain today. More interesting to me are the bottom two bands. These are the Lovell Telescope and Mark II telescope at Jodrell Bank Observatory in Cheshire. What is interesting is that they have common spikes. Both telescopes were observing different objects in different parts of the sky but as the spikes are in common, they must be of local origin. My guess would be that they are due to nearby lightning and the overall change from blue to green, as you go from right to left, indicates increasing water in the sky above Jodrell Bank. It looks like it was a wet evening in Cheshire.

Posted in astro blog by Stuart on Saturday 06th Sep 2008 (23:05 BST) | Permalink
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