Download - Climate and Global Change Notes 22-1 Midlatitude Cyclones Global Circulations (Con’t) Midlatitude Cyclones Air Masses Fronts Cold Warm Occluded Lifecycle

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)


22-2


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


22-3


Air Masses (Con’t)

• Source regions


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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



22-5


Cold Fronts

• Cold air advancing and replacing warmer air

Warm Fronts

• Warm air advancing and replacing colder air


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



22-7


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.


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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


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Life Cycle

QuickTime™ and aVideo decompressor

are needed to see this picture.


22-10


Example

• Low-pressure system over U.S.

http://visibleearth.nasa.gov/Sensors/Terra/


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Example

• Low-pressure system off Australia

http://earthobservatory.nasa.gov/NaturalHazards/natural_hazards_v2.php3?img_id=2108


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Example

• Global View

http://visibleearth.nasa.gov/Sensors/Terra/


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Example

• Surface mapfor 15Z9 May ‘02

Surface data

High and lowpressuresystems

Fronts

Radar

http://weather.unisys.com/surface/sfc_map.html


22-14


Example

• Surface mapfor 00Z31 Mar ‘98

Surface data

High and lowpressuresystems

Fronts

Radar

QuickTime™ and aVideo decompressor



22-15

Jet Stream

PGF - Pressure gradient force vectorGeostrophic wind vectorPressure surfacesJet stream core

Structure


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Jet Stream

Seasonal Variation in the Jet Stream

• Summer- Weaker- Farther north

• Winter- Stronger- Farther south

• Moves with the Sun


22-17

Jet Stream

Variation in the Jet Stream

• Sometimes two jet streams

- Midlatitude or Polar Jet

- Subtropical Jet

QuickTime™ and aTIFF (Uncompressed) decompressor


http://rst.gsfc.nasa.gov/Sect14/Sect14_1c.html

Download - Climate and Global Change Notes 22-1 Midlatitude Cyclones Global Circulations (Con’t) Midlatitude Cyclones Air Masses Fronts Cold Warm Occluded Lifecycle

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