1. The Atmosphere

2. The Atmosphere
The atmosphere is the envelope of gases that surround our planet
It is a very thin layer compared to the radius of the Earth

3. State of the Atmosphere
We discuss and study the atmosphere in terms of the following variables:
Pressure
Temperature
Wind
Humidity
Cloud cover
Precipitation type and amount
Visibility (distance one can see horizontally)

4. Weather vs. Climate
Weather is the state of the atmosphere at a particular time and a particular place.
Climate is the long-term state of the atmosphere at a particular location.

5. Atmospheric Composition
Dry air (neglecting water vapor) is composed of the following gases:
Nitrogen (N2) = 78%
Oxygen (O2) = 21%
Argon (Ar) = 1%
Trace Gases
Dust, bacteria, and other particulates

6. Atmospheric Composition
Trace Gases
Gases that are only found by examining a million or billion air molecules
Examples include:
Carbon Dioxide (CO2) = 340 ppmv
Neon (Ne) = 18 ppmv
Helium (He) = 5 ppmv
Methane (CH4) = 2 ppmv
Hydrogen (H2) = 0.5 ppmv

7. Composition of Air
There are many different types of gasses in the atmosphere
They include nitrogen, oxygen, argon, carbon dioxide and other noble gasses
The gas that is most abundant is nitrogen

8. Vertical Layers of the Atmosphere
The Earth’s atmosphere has 4 distinct layers that are identified by the way temperature changes with height. These layers are:
- Troposphere
- Stratosphere
- Mesosphere
- Thermosphere

9. Vertical Layers of the Atmosphere (continued)
Layers of the atmosphere are determined based on how temperature changes

11. Troposphere This is the layer closest to the Earth’s surface
Almost all the weather phenomenon we know of occurs in this layer.
The depth of the troposphere varies by the season (deeper in summer)
Temperature on average decreases with height.

13. Stratosphere The next layer above the troposphere
The boundary between the stratosphere and troposphere is called the tropopause.
The ozone layer is found here
Some clouds can form here near the poles
Temperature increases with height
Very little mixing occurs between the troposphere and stratosphere.

15. Mesosphere The mesosphere is the next layer above the stratosphere.
Clouds are rare in the mesosphere.
Temperature decreases with height in the mesosphere

17. Thermosphere
The thermosphere rests above the mesosphere, and no clouds exist.
Temperature increases with height in the thermosphere.
The highest temperatures for the atmosphere occur in the thermosphere, but it doesn’t feel hot because the atmosphere is so thin up there.

19. Thermosphere (continued)
This is where most small meteorites burn up and is also the location in the atmosphere that the northern lights occur (aurora borealis)

24. Atmospheric Density
Density and pressure in the atmosphere decrease exponentially with height
Approximately 75% of the total atmosphere is in the troposphere
Approximately 99% of the atmosphere is the troposphere and stratosphere