1. Bellwork 4/10 Please, turn in your Sling Psychrometer Lab
In your own words, describe the difference between Relative Humidity & Dew Point?
Think back to our oceans unit…which was more dense, cold water or warm water?
 What happens when cold water & warm water meet?

2. Bellwork 4/10 Please, turn in your Sling Psychrometer Lab
What is relative humidity?
Why did the wet-bulb & dry-bulb thermometers have different temperatures?
Why does relative humidity NOT give us a good indication of how much water is in the air?

3. Things to keep in mind today…
Cooler air = more dense
We are always comparing an air parcel to its surroundings
There are processes that FORCE air upwards

4. Adiabatic heating/cooling
Adiabatic temperature changes occur when
Air is compressed
Motion of air molecules increases
Air will warm
Descending air is compressed due to increasing air pressure
Air expands
Air parcel does work on the surrounding air
Air will cool
Rising air will expand due to decreasing air pressure

5. Adiabatic Rates Dry adiabatic rate Unsaturated air
Rising air expands and cools at 10˚C per 1000meters
Descending air is compressed and warms at 10˚C per 1000 meters

6. Adiabatic rate Wet adiabatic rate starts at condensation level
Air has reached the dew point
Heat released by the condensing water reduces the rate of cooling
Rate varies from 5˚C to 9˚C per 1000 meters

7. Adiabatic cooling of rising air

8. Stability of air Stable air Unstable Air Resists vertical displacement
Often results in widespread, thin clouds
Precipitation, if any, is light to moderate
Air parcel is _______________ than the surrounding air
Unstable Air
Rises until it reaches air of equal temperature
Acts like a hot air balloon

9. Environmental Lapse Rate
Temperature decrease in the troposphere
Not a constant; must be measured regularly
Average is about 6.5 ⁰ C per 1000m
Ranges from about 5⁰C-12 ⁰ C

10. Types of Stability Absolute stability
Environmental lapse rate is less than wet adiabatic rate
Air is cooler than its surroundings and, therefore, sinks
Most stable conditions occur with a temperature inversion
Cooler air near surface, warmer air aloft

11. Absolute stability

12. Types of Stability Absolute instability
Environmental lapse rate is greater than the dry adiabatic rate
Air is warmer than its surroundings and, therefore, rises

13. Absolute instability

14. Conditional Instability
More common type of instability
Environmental Lapse Rate between they dry and wet adiabatic rate
Depends on whether air is saturated
Unsaturated air = stable
Saturated air = unstable

15. Conditional instability

16. Stability of air Determines to a large degree
Type of clouds that develop
Intensity of the precipitation