climate and global change notes 22-1 midlatitude cyclones global circulations (con’t) midlatitude...
TRANSCRIPT
Climate and Global Change Notes
22-1
Midlatitude Cyclones
Global Circulations (Con’t)
Midlatitude CyclonesAir MassesFronts
ColdWarmOccluded
Lifecycle
Jet StreamStructureSeasonal Variation
Science Concepts
The Earth System (Kump, Kastin & Crane)
• Chap. 4 (pp. 63-66)
Climate and Global Change Notes
22-2
Midlatitude Cyclones
Air Masses
• An air mass is a large blob of air with similar temperature and moisture characteristics
• Two reasons for differences in these properties- Earth’s uneven heating- Earth’s surface has land and water
• These properties depend on the source region of the air mass
Source regions Characteristic- A = Arctic Coldest- P = Polar --- T = Tropical --- E = Equatorial Warmest- m = maritime Moist- c = continental Dry
Climate and Global Change Notes
22-3
Midlatitude Cyclones
Air Masses (Con’t)
• Source regions
Climate and Global Change Notes
22-4
Fronts
• Boundary between two air masses
• Types of fronts
- Cold front - cold air advancing and replacing warmer air
Blue line or
- Warm front - warm air advancing and replacing colder air
Red line or
- Stationary front - Warm and cold air both stationary. Alternating red and blue line or
Midlatitude Cyclones
Climate and Global Change Notes
22-5
Midlatitude Cyclones
Cold Fronts
• Cold air advancing and replacing warmer air
Warm Fronts
• Warm air advancing and replacing colder air
Climate and Global Change Notes
22-6
Mature Midlatitude Cyclone
• Cyclonic circulation - Low pressure system
• Counterclockwise circulation in the northern hemisphere
• Warm air mass moves north while cold air mass moves south
Midlatitude Cyclones
Climate and Global Change Notes
22-7
Midlatitude Cyclones
Occluded Fronts
• Boundary that separates the new cold air mass (to the west) from the older cool air mass already in place north of the warm front
• Cold fronts move about twice as fast as warm fronts
“Got a job as a weather girl.” he said. “Channel three.”
“Jenn Stone,” I said. “That’s where I’ve see her.”
“That’s her with the low-pressue areas,” Jesse said, “and the occluded fronts waving at the weather charts just like she knew.”
Robert B. Parker, Blue Screen, p. 198.
Climate and Global Change Notes
22-8
Midlatitude Cyclones
Life Cycle
• Six Stages
- a) Cyclonic shear- b) Frontal wave- c) Wave cyclone -
open wave,mature cyclone
- d) Shrinking warmsector
- e) Occluded system- f) Dissipating stage
Climate and Global Change Notes
22-9
Midlatitude Cyclones
Life Cycle
QuickTime™ and aVideo decompressor
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Climate and Global Change Notes
22-10
Midlatitude Cyclones
Example
• Low-pressure system over U.S.
http://visibleearth.nasa.gov/Sensors/Terra/
Climate and Global Change Notes
22-11
Midlatitude Cyclones
Example
• Low-pressure system off Australia
http://earthobservatory.nasa.gov/NaturalHazards/natural_hazards_v2.php3?img_id=2108
Climate and Global Change Notes
22-12
Midlatitude Cyclones
Example
• Global View
http://visibleearth.nasa.gov/Sensors/Terra/
Climate and Global Change Notes
22-13
Midlatitude Cyclones
Example
• Surface mapfor 15Z9 May ‘02
Surface data
High and lowpressuresystems
Fronts
Radar
http://weather.unisys.com/surface/sfc_map.html
Climate and Global Change Notes
22-14
Midlatitude Cyclones
Example
• Surface mapfor 00Z31 Mar ‘98
Surface data
High and lowpressuresystems
Fronts
Radar
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Climate and Global Change Notes
22-15
Jet Stream
PGF - Pressure gradient force vectorGeostrophic wind vectorPressure surfacesJet stream core
Structure
Climate and Global Change Notes
22-16
Jet Stream
Seasonal Variation in the Jet Stream
• Summer- Weaker- Farther north
• Winter- Stronger- Farther south
• Moves with the Sun
Climate and Global Change Notes
22-17
Jet Stream
Variation in the Jet Stream
• Sometimes two jet streams
- Midlatitude or Polar Jet
- Subtropical Jet
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
http://rst.gsfc.nasa.gov/Sect14/Sect14_1c.html