Probable dew forming on instruments at Chilbolton Observatory
I’ve been coming up to speed on watching a half pyrgeometer at the Chilbolton Observatory, Hampshire, England, close to where I live and so the conditions here are very similar. I’d previously observed what I took to be dawn dew/frost forming.
For investigation purpose I’ve scripted grabbing a set of images from their web site for the previous day, for occasional use. (Lua 5.1, ask if you want a copy, just a quick hack)
First set was for yesterday. On looking I noticed after dusk a notch in some of the data which looks right for dew forming. According to the BBC weather centre at 00:30, no frost in this area… I looked at the thermometer here, 1.2C not well exposed, checked outside, ground frost. I’ve been out late when there was already a heavy dew.
The images are aligned and vertical gauge lines added.
Looks like the LIDAR suffers from dew too.
Humidity instrument is somewhat suspect on accuracy (reluctant to go exactly 100%), nothing unusual are poor instruments generally. The exact location relative to the other instruments will matter since the effect is progressive and localised. A difference in timing is to be expected.
A surprise is an effect on the wind data, although with such light wind maybe dew forms too. On the other hand strange minor airflow change does happen as atmospheric conditions change.
The pyrgeometer shows an excess incoming radiation figure, where for some parts of the world will often happen twice a day. Looks like a few percent increase when integrated. I don’t know what this would do to a net instrument.
set of plots of thumbnail photo for 16th Jan 2013 here (100k .zip)
Hourly sky photographs are taken, a very useful check on what is actually there. However, it’s a pity a low light camera is not used. This is not hard to arrange these days. Clouds etc. at night can be shown, anything is better than nothing. The cloud radar is only intermittently active.
I suspect this is outside of normal interest and yet night-time atmospheric conditions are under-represented in data and knowledge, as well as highly critical to planetary information. Half the data.
I thank Chilbolton and their supporters for providing plots via the web.
Previous stuff http://tallbloke.wordpress.com/2013/02/11/discussions-on-pyrgeometers-ir-measurement/
Post by Tim Channon