1. Meteorology
12.1 The Causes of Weather

2. Weather Meteorology is the study of atmospheric phenomena
Weather is the current state of the atmosphere.
This is usually measured in minutes, days and weeks

3. Climate
Climate is the weather for a long period of time for a given location.
Usually averaged over 30 or more years.
Ex. The climate is hot and humid in Miami, but it is snowing there today.

4. Air Masses
An air mass is a large body of air that takes on the characteristics of the area over which it forms.

6. Types of Air Masses Moisture Maritime vs. Continental:
Maritime air masses form over water- have more moisture
Continental air masses form over land- they are drier

7. Types of Air Masses Temperature Tropical vs. Polar
Tropical air masses form closer to the equator- warm
Polar air masses form closer to the poles- cold
Arctic air masses are extremely cold

8. Source Regions
Combine Moisture and Temperature titles to name air masses.
Name them after the regions where they form.
Continental Tropical(cT) will form over land near the equator. Ex. Brazil, Mexico
Maritime Tropical(cM) will form over water near the equator. Ex. Gulf of Mexico

9. Examples: Continental Polar(cP) Continental Tropical(cT)
Maritime Polar(mP)
Maritime Tropical(mT)
Arctic(A)

10. Coriolis Effect
The Earth spins on its axis. This causes air particles to deflect to the left in the N. Hemisphere & to the right in the S. Hemisphere

11. R L L R

12. Wind Systems Three wind zones in each Hemisphere Trade Winds
Prevailing Westerlies
Polar Easterlies

13. Wind Zones
The trade winds occur from the equator to 30ºN and 30ºS. The winds at the equator are called the doldrums and the ones at the 30º mark are called the horse latitudes.
The prevailing westerlies are between 30ºN and S up to 60ºN and S in a pattern opposite of the trade winds. They are responsible for moving most weather across the US and Canada.

14. The polar easterlies are between 60ºN and S and the poles. (90ºN and S)

16. Jet Stream
A stream of air that circulates the globe. Caused by differences in pressure between the wind systems.
Trade and Westerlies
Westerlies and Easterlies

21. Fronts
A front is the narrow region separating two air masses of different densities. These differences are due to differences in temperature, humidity, and pressure.
Cold
Warm
Stationary
Occluded

23. -Thunderstorms often occur along the front
Page in RED BOOK!
Cold Front – Cold dense air displaces warm air and forces the warm air up along a steep front
-Thunderstorms often occur along the front
On a weather map: solid blue line with blue triangles that point in direction of the front’s motion

24. Cold Fronts
Cold Fronts occur when a cold air mass runs into a warm air mass, forcing the warm mass to rise.(notice cloud types!)

26. Warm Front – Advancing warm air displaces cold air
- Extensive cloudiness and precipitation
On a map: solid red line with regularly spaced, solid red semicircles pointing in the direction of the front's motion.

27. Warm Fronts
When warm masses run into cold masses and slowly displaces it. (notice clouds!)

29. - Light wind and precipitation
Stationary Front – Two air masses meet and neither advances; air masses “stall”
- Light wind and precipitation
On a map: combination of short segments of cold and warm front symbols

30. Stationary Fronts
Stationary Fronts occur when front run in parallel opposite directions

32. - Strong winds, heavy precipitation
Occluded Front – Cold air mass moves so rapidly that it overtakes a warm front
- Strong winds, heavy precipitation
On a map: alternating purple triangles and semicircles that point toward the direction of motion.

33. Occluded
Occluded Fronts occur when two cold fronts “pinch” a warm front up.

35. Front Video

36. High Pressure Systems
High Pressure Systems- Air sinks, then hits the Earth’s surface and spreads out.
Wind blows away from high pressure.
Clockwise in N. Hemisphere
Associated with fair weather

37. Low Pressure System Low Pressure System- Air rises, must be replaced.
Wind blows toward center of low pressure
Counter-Clockwise in N. Hemisphere
Associated with clouds and precipitation