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Author Topic: Why is it colder higher in the atmosphere?  (Read 3177 times)

Pinchas Goldberg

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Why is it colder higher in the atmosphere?
« on: 10/05/2011 04:01:02 »
Pinchas Goldberg  asked the Naked Scientists:
   
Hi
 
Please can you also explain why if the sun heats the earth (as we all understand it to do), and if you were to go to a planet closer to the sun you'd fry, and freeze if you went to a planet further away, then why when we fly in a plane, and get closer to the sun, is the outside temperature often many degrees below zero? If I'm closer to the sun my a few meters, it should be warmer in the sky, not colder?
 
Thank you again for such interesting shows.
 
I look forward to hearing from you.
 
From Johannesburg
 
Yours
Pinchas Goldberg

What do you think?
« Last Edit: 10/05/2011 04:01:02 by _system »


 

Offline yor_on

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Why is it colder higher in the atmosphere?
« Reply #1 on: 10/05/2011 22:56:54 »
That one has to do with atoms.

1. Temperature in the atmosphere is (mostly) kinetic energy released by the atoms 'jiggling and colliding' with each other, radiating out heat. The jiggling is the atom vibrating by itself (its 'kinetic energy') with the collisions releasing some of that as heat. Most of the jiggling comes from the suns interaction with atoms, that depending on the photons energy will release a electron, or not. That phenomena is also referred to as 'the photoelectric effect' and depends on the frequency of the photon, and thus its 'energy'. Around 49 percent of that heat is in form of IR, the rest comes in a mix of visible and non visible radiation.

2. The higher you come, the fewer atoms.

3, Some atoms/molecules will trap heat for a very long time, as CO2 (hundreds of years), also referred to as the GWP (Global Warming Potential.) Others may contain more heat, as methane, but then also release it over a much shorter period (years).

"Two elements, nitrogen and oxygen, make up 99% of the volume of air. The other 1% is composed of "trace" gases, the most prevalent of which is the inert gaseous element argon. The rest of the trace gases, although present in only minute amounts, are very important to life on earth. Two in particular, carbon dioxide and ozone, can have a large impact on atmospheric processes. Water vapor, also exists in small amounts. It varies in concentration from being almost non-existent over desert regions to about 4% over the oceans"

Then you have the fact that the earth receives almost twice as much heat from the atmosphere as it does from the sun. And that's because the sun only can shine at any given point approximately half a day, morning to evening, whilst those atoms in the atmosphere never stops colliding. Also it is so that under the nighttime Earth releases some of the heat it trapped under the day as IR radiation, and we also have to consider that Earth have its own source(s) (volcanoes for example) of heat seeping from its core.

==

Earth Heat Gains

short-wave radiation from the sun...............34.7%
long-wave radiation from the atmosphere.........65.3%

Earth Heat Losses
Long-wave radiation to the atmosphere...........75.5%
Long-wave radiation to space.................... 4.1%
Evaporation from oceans/lakes/land..............15.6%
Convection and conduction to atmosphere......... 4.8%

Atmospheric Heat Gains
Short-wave radiation from the sun...............11.9%
Heat to atmosphere from condensation............14.4%
Heat to atmosphere from convection/conduction... 4.4%
Long-wave radiation from earth..................69.4%

Atmospheric Heat Losses
Long-wave radiation Radiated to Space...........40.0%
Long-wave radiation radiated to earth...........60.0%

These values derived from graphs and charts from the textbook "Meterorology
Today," (4th Ed.) by C. Donald Ahrens.
===

But it is also so that you can find layers of air high up that is warmer than further down.

Why that is, seems primary due to the ozone layer that absorbs solar ultraviolet radiation in the stratosphere. And in the thermosphere (around 80 km from the surface) it is due to the the small amount of residual oxygen present, getting charged electrically by the suns radiation, particles there can become as hot as 2,000C, but they are very few. It is a very complicated 'mechanism', the atmosphere, and there are a lot of non-linear interactions creating our daily weather, and temperature.

So, although particles can jiggle more the closer they are to the sun, they need to be in certain concentrations to get that colliding going full-time releasing 'heat', and that has to do with the atmospheres density, in its turn created by the gravity primary.

Also I can guarantee that I missed some things here :)
It's tricky.
« Last Edit: 11/05/2011 06:16:31 by yor_on »
 

Offline Soul Surfer

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Why is it colder higher in the atmosphere?
« Reply #2 on: 13/05/2011 18:43:09 »
That seems to be a needlessly complicated reply that does not explain the important fact.  Here is the full story from first principles.

A gas consists of lots of atoms and molecules flying around and bumping into each other at high speed when a gas is confined this bumping of the atoms on the walls of the container causes the gas to exhibit a pressure.  The faster the atoms and molecules are moving (raising the temperature) the greater the pressure is.

The pressure of the earth's atmosphere is effectively the weight of all the gas in the atmosphere above the place you are measuring the pressure.  You can think of it as placing a board in the air the molecules hitting either side push evenly so you don't notice any effect

As you move upwards through the atmosphere there is less gas above you so the pressure goes down. 

As you reduce the pressure in a gas you cause it to expand.  Expansion means that there is on average more space between the atoms and molecules so the speed they are moving goes down i.e. the temperature goes down this is called adiabatic expansion.  You are more familiar with the opposite adiabatic compression as you pump up a bicycle tyre the pump gets hot.

So if gas is pushed upwards in the atmosphere the pressure goes down and it cools down if it didn't the atmosphere would be unstable.

This natural fall in temperature is called the "adiabatic lapse rate"  If air gets hot it expands and rises (convection) and cools down this is how clouds form.

This relationship breaks down at very low pressures near the top of the atmosphere and the speed of the atoms (temperature) rises again.  this is because the pressure changes so slowly that the forces of convection are too weak to control the airflow.
« Last Edit: 17/05/2011 09:03:15 by Soul Surfer »
 

Offline yor_on

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Why is it colder higher in the atmosphere?
« Reply #3 on: 17/05/2011 00:11:15 »
Nice explanation, and yes, I complicated it reading yours :)

One thing though "So if gas is oushed upwards in the atmosphere the pressure goes down and it cools down if it didn't the atmosphere would be unstable."

As I understands it the 'heating/radiating' we see on Earth is primary the result of those colliding, radiating heat. And the collisions becomes fewer the more space there is with less heat released, but there is also the possibility of those 'fewer molecules/atoms' increasing their energy due to the Suns radiation, as described before.
 

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Why is it colder higher in the atmosphere?
« Reply #4 on: 17/05/2011 09:03:58 »
The atmosphere is largely transparent and transparency implies that light energy is not absorbed, therefore there is not much heating of the atmosphere by direct sunlight. The atmosphere is warmed by contact with the hot earth and buildings together with the longer wavelength infra red emitted by these things which is absorbed by gas molecules.
 

Offline CZARCAR

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Why is it colder higher in the atmosphere?
« Reply #5 on: 17/05/2011 15:25:30 »
2 similar solar panels, 1 0n earth & 1 in outer atmosphere---which receives more energy?....the earth is a heater?
 

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Why is it colder higher in the atmosphere?
« Reply #5 on: 17/05/2011 15:25:30 »

 

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