1. State of the Atmosphere

2. Temperature Temperature – a measure of the movement of molecules
Greater number of molecules or faster the movement = hotter the temperature
Lower number of molecules or slower the movement = colder the temperature
Measured by thermometer

3. Heat
Heat is the transfer of energy that occurs due a difference in temperature
Direction of heat flow depends on temperature
Heat flows from hotter objects to cooler objects

4. Heat VS Temperature
Heat transfers energy that fuels atmospheric processes, while temperature measures the heat energy
Temperature is measured in Farenheit, Celsius, and Kelvin
Prefer measurements of temperature in Celsius for weather temperature, because convenient for freezing point (0C) and boiling point (100C)

5. Dew Point
Dew point is the temperature at which air must be cooled at constant pressure to reach saturation
Saturation = point at which air holds as much water vapor as it can
Until air is saturated, condensation cannot occur
Condensation = occurs when matter changes state from a gas to a liquid

6. South American Gray Fox
Dew Point
Important for desert animals whose only source of water comes from dew left on plants
South American Gray Fox
Kangaroo Rat

7. Vertical Temperature Changes
In the troposphere, temperature decreases as altitude increases
Why? As altitude increases, move away from source of heat (Earth’s surface)

8. Vertical Temperature Changes
Air pressure decreases as altitude increases
As air mass moves upward, pressure decreases and the air mass expands as a result
Molecules are further apart, and collisions between molecules decrease, causing temperature to decrease
If air continues to rise, will eventually cool to condensation temperature and form clouds
Height at which condensation occurs is called lifted condensation level (LCL)

9. Air Pressure and Density
Just like water, air exerts pressure on our bodies
Gravity from Earth pulls air particles toward the center of Earth
We don’t feel air pressure because adapted to it
Density of air related to the number of particles occupying a particular space
Gases from upper layers of atmosphere push down on lower layers to compress particles and increase density

10. Wind
Wind occurs when air moves from areas of high pressure to areas of lower pressure
Cool air is denser than warm air, and sinks and forces warmer air upward
Air moves in response to density imbalances caused by unequal heating and cooling of Earth’s surface
Wind measured in miles/hour or ships at sea measure wind in knots
1 knot = 1.85 km/hr

11. Wind Wind changes with height in altitude
Near Earth’s surface, wind encounters friction that results from contact with trees, water, hills, sand, etc
As you get further from Earth’s surface, less friction encountered by wind, so wind speeds increase

12. On surface of sand dunes?
Wind
Would you expect wind speeds to be faster or slower…
On surface of sand dunes?
On surface of water?

13. Relative Humidity Amount of water vapor in air is called humidity
Relative humidity is a term used to describe the amount of water vapor that exists in a gaseous mixture of air and water vapor
Relative humidity varies with temperature
Warm air holds more humidity than cold air
Expressed as a percentage