Buzzy--Bee

So this morning at 6.45am when I left home the temperature was 24 degrees already. Now it is in the high 30s.

So what causes the thick fog that accompanied me for the first 15 mins of my journey to work? In the UK I would have associated that with cold conditions.

Just interested......

Buzzy

AndyR1976

OK, I could write an essay on this - my first degree was Environmental Science.....

Simple explanation

Fog is developed when you drop the air temperature so that the atmosphere is less capable of holding water vapour - no different to a cloud.

In Australia, when it is hot during the day, the air can hold a lot of moisture and the heat causes evaporation......

The hotter it is (all other things being equal) the more water the air (atmosphere) can hold.... so when the temperature drops the water held in the atmosphere forms as water vapour and forms FOG or CLOUD.

So if its 30 degrees during the day, he atmosphere can hold a lot of water....... when the temperature drops (say, to 17 degrees), the atmosphere is less able to hold that moister and fog forms.


In Australia we often see this phenomonon in late afternoon thunderstorms - during a hot day, there is a large amount of evaporation and the hot air is capable of holding lots of moisture......late in the afternoon, as the temperature drops the atmosphere is less capable of holding that moisture and clouds start to form (there is a whole science based on cloud formation).....eventually, the atmosphere is not able to hold the moisture and we get those heavy afternoon thunderstorms.

This is a pretty simple explanation and there are other factors - one importatn one is temperature inversion (also called meteorological inversion) which we experience on the east coast and which famously produces fog and smog in cities such as San Francisco..

Basically, air is usually warmer near the ground, and gets colder as you rise away from the earths surface - under some conditions, usually related to the temperature of the ground and ocean the temperature 'inverts' with a patch of colder air is held against the surface of the earth by warmer air above - the inversion 'hold down' any accumulated moisture/fog/smog, resulting in the famous fog pictures that we see in San Francisco and other places (such as the Blue Mountains for example....)

Places that have big temperature variations are the places where fog forms the most easily (not, as many people assume, the colder places).

Buzzy--Bee

Great. That explains it. Thank you.

Buzzy

Nerine

Temp here was 23 at the same time of day, how come we don't get the fog? Doesn't get quite as hot during the day though: 28 now but arid enough to do without the air con.

AndyR1976

Jeeez - what is this, a FOG HUNT.......

It depends on how much humidity is in the air also (plus a million other factors)....

Just cause its hot then gets cold does not GUARNATEE that there will be fog....

If you put an empty bottle in the freezer do you get ice? Or just cold air???

Nerine

maybe I just need to get up earlier?