I could be for inversion.How are they formed?

I could be for inversion.
How are they formed?

Posted on Trivia Section
MurrayHay avatar
1 month ago #2
MurrayHay
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An inversion is where air at a higher altitude is not as cold (or in fact it could be actually warmer than lower air) as it should be due to simple adiabatic expansion.

Ok starting with the simple Physics:

1) Take a certain volume of air, as air is transparent (to HEAT as well as visible spectrum) the sun does not directly heat the air for practical purposes, rather it is heated (or cooled) by contact with the surface.

2) Once the air (which was surface heated) is off the surface if we were to loosely wrap it in a bubble of cling film to stop it mixing with any other air that 'bubble' will in simple terms have a fixed amount of energy, we generally express the energy as 'temperature'.... however the bubble if it moves higher is surrounded by LESS dense air so it will expand (remember loosely wrapped so free to expand) hence the air now takes up a greater volume but has the same amount of energy to 'spread around'... as a result it's temperature declines at a predictable rate known as "DALR" (Dry Adiabatic Lapse Rate) the D for 'dry' simply means the Relative Humidity is not yet '100%' so no visible moisture exists (i.e. we are still below 'cloud base'). The standard value given for DALR is 3*C per 1,000ft.

3) Sample numbers example: Say for a day when the air at the beach (sea level) is 15*C DALR would predict (given a near 'blue sky day' with just some whispy high altitude ice clouds in the far distance) the air temp at 1,000ft to be 12*C and the 2,000ft level to be expected to be 9*C, with a 5,000ft level of 0*C and a 10,000ft temp of -15*C

4) High altitude (ice) clouds approaching is a classic sign of an approaching Warm Front' so later in the day with the cirrus (ice) clouds now well established above us we could expect a temp 'profile' of > Sea Level 15*C, 1,000ft 12*C and 2,000ft giving 9*C... but perhaps 5,000ft now having a temp of say 7*C and 10,000ft could be only -2*C..... all due to the leading edge of the 'wedge' of 'Warm Air' (it is a RELATIVE term) due to the arriving Warm Front being above us....

5) So an 'inversion' most commonly is when air at altitude above us is 'Warmer' than it 'should be'...

6) NOTE 'inversions' strictly speaking is a term that can also, in practice, be used to describe the situation where air LOWER than us (typically seen in a calm valley in the winter while we are on a soarable hill top site) is 'colder' than it 'should be', this type of 'inversion' is not associated with 'frontal (warm) systems' rather it is a 'micro climate' with cool (often from overnight) air 'pooling' due to gravity...

Yours Murray Hay

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