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Layers of the Atmosphere. 2009. Pressure is a force that acts over a certain area. Liquids and gases are fluids. Fluids are any material that is able to flow. Fluids exert pressure because of the motion of their particles.

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Pressure is a force that acts over a certain area.

Liquids and gases are fluids. Fluids are any material that is able to flow. Fluids exert pressure because of the motion of their particles.

Pressure will always move from a high pressure to a low pressure area. The pressure will always try to equalize. You see this when you get a hole in your bicycle tire.

inflating example
Air inside a ball pushes against the sides. The more air we put in a ball, the more the molecules push. So the pressure increases as we add air.Inflating example
air pressure
Air pressure is the result of the column of air that is above you.

There is so much air above you that at sea level you have 14.7 lbs/in2 pushing on you.

Gravity causes most of the air to be pulled down to the surface.

Air Pressure
why are we not crushed by air pressure
Why are we not crushed by air pressure?
  • Air pressure is equal in all directions.
  • So air pushes equally in all sides of us. The forces are balanced!
units of air pressure
TV weather stations and aviation use inches of mercury.

Meteorologists (and the NWS) use millibars, an SI unit.

Units of Air Pressure
altitude and density
As the air pressure decreases, the density of the air decreases. The air particles are not squashed together as tightly the higher one goes. This is caused by gravity!

The air at sea level and at 6km has the same 21% oxygen, but at 6km there are fewer molecules, so you take in less oxygen with each breath.

Altitude and Density
temperature and the troposphere
Troposphere: temperature at surface is warmed by the earth absorbing energy from the sun.

Convection currents carry the heat upward, so the air cools as it rises.

The air cools by about 6.5°C for every 1-km above the ground.

Temperature and the Troposphere
temperature and the mesosphere
This layer does not absorb energy from the sun, so it starts to cool again.

Without greenhouse gases, energy pretty much passes straight through!

Temperature and the Mesosphere
temperature and the thermosphere
Solar radiation first hits this layer, so the few particles that are here can gain lots of energy. They move rapidly, so they have a very high temperature.

But the air is so thin here that it takes special instruments to measure the temperature accurately.

So even though it is very hot (over 1000°C), it would feel cold because there are so few particles to transfer heat to you.

Temperature and the Thermosphere
the troposphere
The Troposphere
  • Lowest (inner) layer
  • weather occurs here
  • we live in it.
  • “tropo” means turning or changing conditions
  • depth varies from 9km above the poles to 16km at the equator
  • shallowest (least thick) layer, but contains most of the mass (90%).
the stratosphere
The Stratosphere
  • “strato” means layer or spreading out
  • Contains the ozone layer which absorbs energy and causes the temperature to rise
  • The ozone layer protects the surface from dangerous UV rays
the mesosphere
Drop in temperature marks beginning of mesosphere

“Meso” means middle

Most meteors burn up here

The Mesosphere
the thermosphere
The Thermosphere
  • Very top layer
  • Air is very, very thin, about 1/1000th as dense as the air at sea level
  • “Thermo” means heat
  • Extends from 80km to space
  • No definite outer edge
  • Very hot (over 1000°C), but since air is so thin it would not feel warm at all.
  • Divided into two parts, the ionosphere and the exosphere
the ionosphere
The Ionosphere
  • Energy from sun strips the electrons from the gas molecules creating charged particles called ions.
  • Radio waves can bounce off of ions, allowing radio waves to travel great distances.
  • The aurora borealis (Northern Lights) occur here
the exosphere
The Exosphere
  • “Exo” means outer
  • Extends for 1000’s of miles
  • Satellites orbit here
  • No definite edge
  • Molecules gradually escape out into space