Friday, 2 March 2012

When is it foggy and when is it misty?


Friday 2nd February 2012
A very foggy start.
It took the sun a long time to break through.
Can you spot the impostor masquerading as a swan?


When is it foggy and when is it misty?
Apparently it is foggy when visibility is less than 1km. Otherwise it's mist (assuming it's not just a clear day!). If you're flying a plane, mist is between 999m and 2km, but only if relative humidity is over 95%, otherwise it's haze. Hope that's clear.


Fog can form in a number of ways, depending on how the cooling that caused the condensation occurred. It turns out that what we experience so often here on the fens is known as radiation fog. This is caused by the cooling of land after sunset by thermal radiation in calm conditions with clear sky.
The cool ground produces condensation in the nearby air by heat conduction. Radiation fogs occur at night, but can persist all day in the winter months.


Anyway, today's fog inspired me to get out and take some piccies. It was eerie out there, enclosed in a cocoon of fog, from which would loom the occasional grunting tractor.


 

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