Radiation fog

We found this article this morning http://www.mirror.co.uk/news/uk-news/radiation-fog-descends-uk-met-11459412 It's almost like a scare story. These days the word "radiation" is synonymous with radioactivity. But radiation surely means stuff that travels in rays - ie in straight lines. The physics behind this phenomenon is that solar radiation is absorbed by the ground during the day. The ground gets a bit warmer so it radiates infra-red back upwards. It is acting as a "black body" in the technical physics definition of that term, which derives from the observation that black cans of hot water cool faster than silver cans of hot water. On cloud-free nights, the infra-red radiation is free to pass straight back out into space. So the surface of the Earth cools enough for water vapour to dip below the dew point and it then condenses into fog. Fog caused by cooling due to infra-red radiation disappearing into space.