Midlatitude Cyclones

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Midlatitude Cyclones
Science Concepts
Global Circulations (Cont) Midlatitude
Cyclones Air Masses Fronts Cold Warm
Occluded Lifecycle Jet Stream Structure Se
asonal Variation
The Earth System (Kump, Kastin Crane) Chap.
4 (pp. 63-66)
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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 - Earths uneven
heating - Earths 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
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Midlatitude Cyclones
Air Masses (Cont) Source regions
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Midlatitude Cyclones
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
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Midlatitude Cyclones
Cold Fronts Cold air advancing and replacing
warmer air Warm Fronts Warm air
advancing and replacing colder air
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Midlatitude Cyclones
Mature Midlatitude Cyclone Cyclonic
circulation - Low pressure system Countercloc
kwise circulation in the northern
hemisphere Warm air mass moves north while
cold air mass moves south
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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. Thats where Ive
see her. Thats 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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Midlatitude Cyclones
Life Cycle Six Stages - a) Cyclonic shear -
b) Frontal wave - c) Wave cyclone - open
wave, mature cyclone - d) Shrinking
warm sector - e) Occluded system -
f) Dissipating stage
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Midlatitude Cyclones
Life Cycle
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Midlatitude Cyclones
Example Low-pressure system over U.S.
http//visibleearth.nasa.gov/Sensors/Terra/
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Midlatitude Cyclones
Example Low-pressure system off Australia
http//earthobservatory.nasa.gov/NaturalHazards/na
tural_hazards_v2.php3?img_id2108
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Midlatitude Cyclones
Example Global View
http//visibleearth.nasa.gov/Sensors/Terra/
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Midlatitude Cyclones
Example Surface map for 15Z 9 May
02 Surface data High and
low pressure systems Fronts Radar
http//weather.unisys.com/surface/sfc_map.html
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Midlatitude Cyclones
Example Surface map for 00Z 31 Mar
98 Surface data High and
low pressure systems Fronts Radar
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Jet Stream
Structure
PGF - Pressure gradient force vector
Geostrophic wind vector
Pressure surfaces
Jet stream core
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Jet Stream
Seasonal Variation in the Jet Stream Summer -
Weaker - Farther north Winter - Stron
ger - Farther south Moves with the Sun
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Jet Stream
Variation in the Jet Stream Sometimes two jet
streams - Midlatitude or Polar
Jet - Subtropical Jet
http//rst.gsfc.nasa.gov/Sect14/Sect14_1c.html