1. Atmospheric Moisture and Storms
Material from chapter twelve

2. Properties of Water Water is polar (molecule is symetric)
Water actually expands when freezes
Surface tension
Phases changes
Evaporation
Condensation
Most important concept: Latent Heat
The heat which is “hidden” when liquid water is evaporated

3. Humidity
Specifc Humidity: g (water vapor)/ kg of air (actual vapor content)
WARM AIR CAN HOLD MORE WATER VAPOR THAN COLD AIR
Capacity: The maximum amt of water vapor that can be held in the air at any given temperature.
At this point the air is SATURATED (like a soaking sponge – it can’t hold anymore)
Relative Humidity (A PERCENTAGE!! Ie: 75%, 63%):
ACTUAL amt. of vapor in the air DIVIDED by the CAPACITY at that temperature.
Dew Point: The temperature at which the actual, current amt of vapor WOULD be at saturation/capacity.

4. More on relative humidity
Think of cold glass of ice water
The water vapor surrounding immediately condenses on sides of glass
Think of the early morning fog that is formed in predawn hours when it is coolest
And how it burns off and evaporates by noon.
Remember: CLOUDS AND FOG are NOT WATER VAPOR.
Sling psychrometer: A device used to measure relative humidity.

5. Other important terms Adiabatic Processes Stability
The change in air temperature of air parcels by simple rising and falling.
Stability
The tendency for air to rise or to stay put depending on the temperature of surrounding air

6. Clouds
Moisture droplets collecting on condensation nuclei (dust particles/suspended solids)
Types:
Cirrus/Cirriform (high altitude, blown by strongs, look like wispy strands of cotton
Cumulus/Cumuliform:
Fair weather cumulus (small parcels, individual clouds)
Cumulonimbus, tall thunderstorm clouds
Stratus/Stratiform
Blanket of gray clouds covering sky

7. Fog Advection Fog Evaporation fog Radiation fog Orographic fog
Warm humid air mass passing over cold ocean currents by coast creating dense marine fog which California is known for.
Evaporation fog
Cold front comes through turning vapor/humidity above bodies of water to fog
Radiation fog
Temperature drops drastically at night, turning vapor over wet/moist ground to fog (Tule fog)
Orographic fog
Clouds that are close to ground when moving air is chilled at high elevation

8. Lifting mechanisms of air
Convergent
Winds blowing into low pressure and rising (think ITCZ or other low pressure areas
Convection
Smaller scale than other lifting mechanisms
Individual air parcels being heated over dark surfaces and rising
Frontal
Leading edge of air masses causing uplift and condensation at front
Orographic
Air parcels being pushed up a mountainside
Watch:

9. Cold Fronts and Warm Fronts
Please watch video:
And
Midlatitude cyclones
We didn’t cover this in class, and it won’t be on the exam, but it is good to understand the larger picture that warm and cold fronts are related.

10. Tornadoes
Begins as a rolling pin motion where high speed upper atmospheric start spinning the slower surface winds into a rotating column of air.
This rotating column of air can get sucked up and stand on end when comes into contact with cumulonimbus cloud.
Doesn’t become the destructive “tornado” until it touches ground.
Until then it is just a funnel cloud

11. Hurricanes
Also called typhoons and cyclones locally (even though cyclones are a more general term for low pressure centers.
Ingredients
Equatorial low pressure center
Enough coriolis effect (hurricanes are nearly non-existent within 5° of equator)
Warm ocean temperatures
Little to no wind shear (high wind shear can tear apart developing hurricane before it gets large).

12. More videos to watch Formation of tornadoes Formation of hurricanes
Formation of hurricanes