How come air temperature goes down with higher altitudes??

Question

Up to a certain altitiude, then starts going up.

Answer 1

The temperature falls as you rise through the troposphere, rises through the stratosphere, falls through the mesosphere and rises through the thermosphere. I wrote a piece about this for a local radio station, here is part of it:

The gases that make up the atmosphere are a mixture. Nitrogen is about 78% and oxygen 21%. The remaining 3% are carbon dioxide, argon, neon, helium, hydrogen, xenon and methane. We should also consider the pollutants, carbon monoxide, ozone, sulphur dioxide, nitrogen dioxide and dust and smoke particles. Finally there is water vapour. This is the most variable of the gases in the atmosphere ranging from 1 - 4% depending on where you are. Gravity helps compress the air in the lower layers so that 90% of the mass of the atmosphere is within 15km of the surface, 99% is below 35km and 99.9% is below 50km. There is very little atmosphere above 50km but it is still important.

At the outer limits of the atmosphere, the molecules of gas are so far apart they are free to move rapidly. Temperature is a way of measuring the motion of molecules, the faster they move, the higher the temperature. It is also in this part of the atmosphere that some of the very short wave radiation from the sun, such as X-rays, is absorbed. This helps to increase the temperature. This layer of the atmosphere is the thermosphere and it is warm at the top of the layer. As we descend towards the surface, the temperature falls as the molecules slow down and we reach a steady layer of temperatures around -80°C from about 90-80 km up.

At 80 km the air starts warming again. The ultraviolet radiation from the sun is absorbed by the oxygen molecules, 02 , breaking them apart into two atoms. These atoms combine with other oxygen molecules to form 03 which is ozone. Ozone is heavier than oxygen and it sinks. The ultraviolet radiation that is absorbed warms the atmosphere as you get lower. This layer is called the mesosphere. The boundary between the mesosphere and the thermosphere at 80km is called the mesopause.

The newly created ozone also absorbs ultraviolet radiation and it breaks up into O2 and O. The oxygen atoms rise to create more ozone. The peak of all this absorption is about 50km up. Below that the temperature starts falling again. The layer where the temperature falls is called the stratosphere and the boundary between the stratosphere and the mesosphere is called the stratopause. Temperatures at the stratopause can be as high as 20°C. Temperatures fall or remain the same through the stratosphere.

The lowest layer of the atmosphere is the troposphere. The earth's surface is heated by the sun. This heats the air in contact with it, which heats the air above that and so on. With no vertical motion of the air, the air in the troposphere gets warmer as you get lower because it is heated from below. The boundary between the troposphere and the stratosphere is called the tropopause and this varies in height from about 3000m at the poles to 15km at the equator. Temperatures at the tropopause vary from about -30°C to -50°C.

All the weather on the planet and most of the cloud occurs in the troposphere. There are some winds and jet streams in the stratosphere which can affect the weather but all the rain is in the troposphere.

So what about the question that started this piece: "Why is it, if hot air rises, that it gets colder as you get higher in the atmosphere?"

It is a well established fact that hot air rises, we are taught this at school and have heard it for centuries. Unfortunately, it is wrong. Hot air does not rise just because it is hot. Less dense air rises or to put it more correctly, denser air sinks and replaces the less dense air. So what's the story about hot air then? Hot air balloons rise.

When you heat air it expands and becomes less dense. Inside a hot air balloon the expanding air fills the balloon and even forces excess air out of the envelope. This means that the air inside the balloon is less dense than the air outside and the balloon rises. As the air inside the balloon cools, air is drawn in from the outside and the density increases. Unless the air is heated again the balloon sinks.

How does this work in the atmosphere? Remember we spoke of how much of the atmosphere is below certain heights? The atmosphere gets denser as we get lower because there is more air lower down. Consequently, a warm dense layer can be overlain by a cooler, less dense layer. The troposphere achieves equilibrium by having the densest air close to the ground which remains denser than the air above it even when it is heated.

Of course the heating of the surface is not uniform. Some areas get hotter than others. Land surfaces get hotter than water surfaces. The variability in heating leads to variability in density and in some areas the air at the surface becomes less dense than the air around it or above it. The denser air moves in and the air rises and we get clouds forming in the rising air.

Next time someone says "Hot air rises", you can say quite confidently "It doesn't, denser air sinks". It is almost guaranteed to start a discussion in the pub or on the golf course but such discussions can be fun - and you will have science to support your argument.

Answer 2

Yes, but Rachel's answer is ... not how it works. At daytime, the sun warms up the earth and the sea and that warms up a thin layer of air right above it. That air being lighter rises and cools down by the adiabatic effect of a lower pressure aloft. The adiabatic cooling is what happens in your fridge after a coolant is compressed then released through a nozzle to create cold. As that parcel of warmer air cools down, it stops rising when meeting an altitude of equal temperature. This is why the air is colder with altitude. But cold air, being warmer, sinks and it does that at night. In fact sometimes it sinks so fast that it creates wind that can be felt on the hill sides. It has even been know in Greenland to have cold air sinking from the glacier into the fjords and destroying Inuit villages. That wind is called a katabatic wind. So, the air rises during daytime and sinks at night. But the latter is a much slower process and that's why it is still the convection, i.e. the rising of the air, that determines the temperature in our troposphere. Yes, because above it, in the stratosphere, the air is warmer with altitude. That is called an inversion: warm air above cold one. Sometimes the same happens in our troposphere and even, at ground level. It happens, for example when at the end of the night, the ground is much colder than the air. Because of the inversion, the air doesn't rise and if there is enough moisture in the air and it has condensed when the temperature felt under dew point, fog will appear. Early morning fog is always a sign of an inversion.

Answer 3

Air is most dense at sea level and is able to hold the most amount of moisture at sea level. Water vapor in the atmosphere is about 99 percent responsible for storing heat energy in the atmosphere. As altitude above the ground increases atmospheric pressure decreases making the air less dense. Since thin air cannot hold as much volume of water vapor as dense air it cannot retain and store as much heat energy. Think of a dry desert region. It may be very hot in the daytime due to ground heating but since the air contains little water vapor it cools rapidly at sunset and can be very cool at night. Since thin, drier air cannot retain heat like dense, more moist air can, the temperature normaly decreases as altitude increases. Being close to the surface does not cuase the higher temperatures. If your on top of a tall mountain your standing on the surface of the earth but the temperature may be freezing even though its August. Temps. do go up once you get above the stratosphere but only if your in the sunlight. If your in darkness temps. are still frigid cold. Since at these altitudes your literaly in the vaccum of space, any objects that are there are exposed to the full effects of the suns radiation.

Answer 4

It's called the lapse rate and usually temperature decreases with height (at least the sort of heights you and i are likely to climb).

Sometimes, usually in anticyclonic condititions, there is a layer next to the surface, where the temperature increase with height.

there is no covection through this layer and smog can get trapped in it

Answer 5

air is not heated by the sun
air is heated by the ground which is heated by the sun
so when you go up
the air is farther from the ground
and is heated less

as far as when you get up it goes up
i have never heard of it doing that