Transcript Air Masses - High School of Language and Innovation

Air Masses
April 28th 2014
Air Masses
Definition:

Air mass - a large dome of air
which has similar horizontal
temperature and moisture
characteristics throughout.
Continental Arctic (cA):
•
•
•
•
Frigid – record low temperatures
Dry - very low dew points
Dense - very high barometric pressure
Usually originate north of the Arctic Circle
 Siberian Express
• Usually once or twice a winter
• very rarely form during the summer
 because the sun warms the Arctic.
Continental polar (cP):
•
•
•
•
Cold and dry
Usually originates in NW Territory of Canada
Influences mainly the northern USA
Responsible for clear and pleasant weather
during the summer
• Usually in winter
• Lake effect snow in Great Lakes areas
Maritime polar (mP):
• Cool and moist
• Originate over N. Atlantic and N. Pacific
• Main Influence - the Pacific Northwest
and the Northeast.
• can form any time of the year
• Generally not as cold as cP air masses
Maritime tropical (mT):
• Warm and very moist
• Originate in the Gulf of Mexico and
the Southern Atlantic Ocean
• Influences the eastern USA
• Usually in the summer
• Responsible for hot, humid summer
days across the South and the East.
Continental Tropical (cT):
• Very Hot and very dry
• Originates in Desert Southwest and
northern Mexico
• Occurs in the summer, rarely in winter
• Usually keeps the Desert Southwest
scorching above 100oF during summer
• Generally clear skies, hot, low humidity
Source Regions
Work Time Activity
Reasoning for Tornadoes


Orographic
Perfection
Meeting of
• Moist - mT
• Hot - cT
• Cool – cP
Tornado Alley

http://www.britannica.com/thunderstorms_tornadoes/video/ocli
wea124v4.mov
Fujita Scale
(NationalAtlas.com)
Fronts and their symbols
Fronts:


Boundary between two air masses
Characterized by shift in weather
 Cold
 Warm
 Stationary
 Occluded
5 Characteristics of a Front





Sharp temperature changes over
a relatively short distance.
Changes in air moisture content
Shifts in wind direction
Pressure changes
Clouds and precipitation
Cold Fronts
• Temperature – drops rapidly
• Pressure – rises steadily
• Clouds – Vertical building
• Precipitation – Heavy along front
• Winds – Strong and shifting
• Typically move faster than warm front
Cold Front
Cold Front
(Fozzy)
Cold Front
In the summer, cold
fronts can trigger:




thunderstorms
large hail
dangerous winds
tornadoes
Graphic Depiction!
Warm Fronts
• Temperature – rises slowly
• Pressure – slight rise, then fall
• Clouds – strato- and cirro• Precipitation – long, steady
• Winds – variable and light
• Typically will have affect for days
Warm Front
Warm Front
Warm Front
Effects of warm fronts


Slow-moving warm front can mean
days of wet weather before warm air
Sometimes water vapor in warm
fronts condense to produce




rain
snow
sleet
freezing rain
Stationary Front
Stationary Fronts
• Temperature – stagnent
• Pressure – slightly fluctuates
• Clouds – altocumulus
• Precipitation – none
• Winds – variable and light
• Can last for days weeks
Occluded Front
Occluded Fronts
• Temperature –
• Warm – gets milder
• Cold – gets colder
• Pressure –
• Warm - slight drop
• Cold – slight rise
• Clouds – cumulus
• Precipitation – steady and light
• Winds – variable and light
Occluded Front
Different Temperatures Different Pressures
Less
Dense
Cool
Air
Less
Pressure
Denser
Warm
Air
More
Pressure
Pressure and Air Movement
Pressure Gradient Force

Difference in pressure over a given
distance---between isobars
 Close together = step pressure gradient
 STRONG winds
 Far apart = gentle pressure gradient
 Light winds
• Just like contour lines
Pressure Gradient Force
Isobaric Maps
Coriolis Effect
 Apparent
force due to the
rotation of the Earth (Think Merry-go-round)
 N. Hemisphere  wind turns right
 S. Hemisphere  wind turns left
 Strength
depends on latitude
and wind speed
Coriolis Effect
Coriolis Effect
Centripetal Force
In-ward directed force
 Allows an object to remain in
circular motion
 Winds moving around high and
low pressure areas
 Clockwise around Highs.
 Counter-clockwise around Lows.

Friction (What a Drag)



The resistance to movement
Surface winds are affected by friction
Why? Ground resistance:
 trees, mountains, houses, buildings, etc.

This drag causes winds to blow across
pressure gradient at the surface.
Pressures All Together
General Planetary Circulation
Winds
 Horizontal
surface
movements at
from WHERE it came
from…not where it is going!!!
 Names
Around Pressure Cells
Pressure Cells

High – In and Up
 Converge at surface
 Ascend in center
 Diverge Aloft

Low – Down and Out
 Converge aloft
 Descend in center
 Diverge at surface
X-section of Planetary Circulation
January Global Pressure Map
January
July Global Pressure Map
July
Summer Highs
Quiz Questions:
1.
2.
3.
4.
Where would you expect there to be the
strongest winds? Why?
Where would you expect there to be the
calmest winds?
Where would you expect clear, cool
skies?
Where would you expect cloudy skies
with the greatest potential for
precipitation?
Work Cited (Incomplete)


http://www.usatoday.com/weather/tg/wamsorce/wamsorce.htm seen 1/03/06
http://www.srh.weather.gov/srh/jetstream/synoptic/airmass.htm