topic 13- geo
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Topic 13
Weather
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Basic Questions
1. Why does Buffalo get lake-effect snow?
2. What are the air masses surrounding NA?
3. What causes air mass instability (lifting)?
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Weather: Topics
Air Masses
Atmospheric Lifting Mechanisms
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General Atmospher ic Circulation
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Air Masses
Distinct volume of air having specific
Temperature
HumidityStability
Moisture and temperature
characteristics of itssource region
Alberta Clipper
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Air Masses Affecting NAMoisture
mfor maritime (wet)
cfor continental (dry)
Temperature (Latitude)
Afor artic
Pfor polar
Tfor tropicalEfor equatorial
AAfor Antarctic
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NA Air MassesWinter
4. Maritime tropical (MA)
Stable, conditionally unstableSubtropical high-pressure cells
Pacific more stable, drier
2. Continental Polar( CP)
NH continentality
Cold, stable, clear skies, high P
Lifts moist, warm air in its path condensation
1.Continental Arctic (CA)
Stable, very cold and very dry
3. Maritime Polar (MP)
Cool, moist, unstable air
Subpolar low-pressure cells
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NA Air MassesSummer
1. Mariritme Tropica(MP) Move northward, onto land
2. CP: Move northward, off
shore
3. CT : Hot, dry air moves into southwest
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Lake-effect Snow
Below freezing cP and cA air absorbs heat and moisture
over Great Lakes
On shore, air becomes chilled heavy snow (200 in.)
Restricted to ~50 to 100 km inland
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Lake-effect Snow
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Atmospher ic L if ting
For air masses to cool adiabatically and form
precipitation, they must lift and rise
Four mechanismsConvergent Lifting
Convectional Lifting
Orographic Lifting
Frontal Lifting
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Atmospher ic L if ting Mechanisms (1)
Trade Winds and ITCZ
Dew point condestion: cloud shape flat bottom
Convergent lifting
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Atmospher ic L if ting Mechanisms (2)
Air warms over
ground surface
Floridaboth convergent
and convectional lifting
Convectional ( local) Lifting
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Atmospher ic Lif ting Mechanisms (3a)
Air lifted, cools adiabatically;
rain shadow
Orographic Lifting: adiabatic heating
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Sierra Nevada
Mt. Range
Cools adiabatically
Heats adiabatically
Rain shadow, WA
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Atmospher ic Lif ting Mechanisms (4a)
.: leading edge
of advancing airmass
A place of
atmosphericdiscontinuity, line
of conflict
between two airmasses
Frontal lifting
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Atmospher ic Lif ting Mechanisms (4a)
Leading edge ofCold air mass: Cold front
Warm air mass: Warm front
Frontal lifting
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Atmospher ic Lif ting Mechanisms (4b)
Steep face due to density anduniform characteristics
Warm air is lifted, coolsadiabatically, and becomesunstable
.: a wind shift, Tdrop,lower P, cumulonimbusclouds, and heavy precipitation
An advance of cp or mp toward mt
A fast advancing cold front can cause violent lifting
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Atmospher ic Lif ting Mechanisms (4c)
Warm air pushes the coolerunderlying air into a wedgea temperature inversion
mTair gently lifted, leadingto cloud development
Leading edge of mt air unable to lift cooler air mass
Larger spatial space than cold air mass.
Warm fronts form a progression of clouds-not as
energetic as an advancing cold front.
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Basic Questions
1. Why does Buffalo get lake-effect snow? cP
air mass migrating across lake2. What are the air masses surrounding NA?
cP, mP, and mT
3. What causes air masses instability (lifting)?Convergence, convection, orography, fronts.
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