Secondary Features of the Atmospheric Circulation

1
Secondary Features of the Atmospheric Circulation

• Air Masses
• Weather Fronts
• Extra-tropical Wave Cyclones
• Chapters 9.1 - 9.2

2
Air Masses
____________________________

• An air mass is a large body of air with fairly
  uniform temperature and moisture characteristics
• It can be several thousand kilometers across, and
  extend upward to the top of the troposphere

3
Air Masses
____________________________

• Air masses acquire their characteristics in
  source regions
• In a source region, air moves slowly or
  stagnates, which allows the air to acquire
  temperature and moisture characteristics of the
  surface

4
Air Masses
____________________________

• Bergeron developed a two-letter classification of
  air masses, based on temperature and moisture
  characteristics
• The first letter identifies the humidity
  characteristics of the air mass
• The second letter identifies the temperature
  characteristics of the air mass

5
Air Masses First Letter
____________________________

• Letter Surface Humidity
• m maritime humid
• c continental dry

6
Air Masses Second Letter
____________________________

• Letter Latitude Temperature
• A Arctic Very Cold
• P Polar Cold or
  Cool
• T Tropical Warm or Hot
• E Equatorial Very Hot

7
Possible Air-Mass Types
____________________________

• cA Continental Arctic
• cP Continental Polar
• cT Continental Tropical
• mP Maritime Polar
• mT Maritime Tropical
• mE Maritime Equatorial

8
Possible Air-Mass Types
____________________________

• There are no cE or mA air-mass types on Earth
• Table 9.1 summarizes air-mass types nicely

9
Air Mass Source Regions
____________________________
Relates to Figure 9.12
10
Air Mass Source Regions
____________________________
11
Air Mass Source Regions Winter
____________________________
12
Air Mass Source Regions Summer
____________________________
13
Air Mass Effects Precipitation
____________________________
14
Air Mass Effects Lake Effect Snowfall
____________________________
15
Weather Fronts
____________________________

• Cold Fronts
• Warm Fronts
• Occluded Fronts

16
Cold Front
____________________________
Destabilized warm air
Steep frontal angle
Position of cold front
Forward speed 15-30 mph
17
Warm Front
____________________________
Warm air may not be destabilized
Shallow frontal angle
Position of warm front
Forward speed 10-15 mph
18
Occluded Front
____________________________
Typically stable air with embedded pockets of
instability
Position of occluded front
Forward speed lt10 mph
19
Extra-Tropical Wave Cyclones
____________________________

• In the middle latitudes, the dominant form of
  weather system is the extra-tropical wave cyclone
  (Bjerknes)
• The wave cyclone is a large inspiral of air that
  repeatedly forms, intensifies, and dissolves
  along the polar front
• Low pressure center
• Fronts are associated with the low

20
Extra-tropical Wave Cyclones
____________________________
21
Extra-tropical Wave Cyclones
____________________________
Stationary Front
Cyclogenesis
Mature Wave
Figure 9.5
Closing Wave
Dying Vortex
Occlusion
22
Structure of a Mature wave cyclone
23
Structure of an Occluding Wave Cyclone
24
Daily Weather Map
____________________________
25
Common Wave Cyclone Tracks
____________________________
26
Wave Cyclones Effect on Weather
____________________________
Figure 9.6
27
(No Transcript)