Transcript Chapter 19: Air Masses

Chapter 19: Air Masses
What are Air Masses?
• Similar Moisture
• Can cover a whole continent
Fronts:
• Leading edge of advancing air mass
• Polar FrontFrigid, Arctic air moves
South from North Pole (Winter
Months)
West to East  From Rocky Mountains
to Maritimes
• Warm Front
• Cold Front
• Stationary FrontWarm and Cold
air boundary remains in one place
• Occluded  Cold overuns warm
mixing the air
Air mass Classifications:
1.
Place of OriginHigh latitudes Arctic/Polar vs. Low Latitudes
Tropical
2.
Overland/Water Continent vs. Maritimes
3.
Stable vs. Unstable Air
•
Stable Air: Lower layers of air are cooler than the air above,
therefore no vertical movement of air (convection) takes
placescharacterized by calm air, clear skies, and no
precipitation.ex. When stable air masses blanket large cities
such as Toronto, air quality quickly deteriorates as pollutants
from factories and vehicle exhaust are unable to rise into the
upper atmo. where they can be dispersed by wind currents. (a.k.a
temperature inversion)
•
Unstable Air: The lower layers of air are warmer than the air
above so air can readily risecloudy, wind, and rain.
Air Masses in North America
Continental Polar (aka Continental Arctic in winter)
• Originates in North Pole extends as far south as
Floridaaffects food crops
• Air mass is very cold, stable and dry.
• Cold air is heavier than warm air, so as this air mass moves
south it stays in contact with the ground.
• Clear, sunny skies and high pressure
Maritime Polar
• Originate over the ocean in temperate and polar regions and
move toward lower lats.
• Northern Pacific (Gulf of Alaska) is where it originates
• Cool, moist, and unstable therefore moisture in BC coast
• Continental arctic is usually kept out by mountain ranges
running south, but when it makes it way into coast and comes
into contact with maritime polar heavy blizzard conditions
occur.
• Summer this air mass is cool, but stable therefore few rainy
days.
Maritime Tropical
Originate in lower latitudes and are
much warmer and far more stable
than Maritime Polar air masses.
Locations such as California get little
ppt. in winter months.
Those the originate in the Gulf of
Mexico, are warmer, wetter and
far less stable, and generate
frequent storms.
Continental Tropical
North from the desert plateau of
central Mexico into the central
Great Plains region of North
America bringing hot, dry
conditions
Air mass associated with tornado and
hurricane activity (Tornado Alley
in the mid United States is
where Maritime tropical air
meets Continental Polar)
This air mass is primarily
responsible for hurricane and
tornado activity!
Animations:
• http://www.classzone.com/books/ear
th_science/terc/content/visualizatio
ns/es2001/es2001page01.cfm?chapte
r_no=visualization
• http://www.classzone.com/books/ear
th_science/terc/content/visualizatio
ns/es2002/es2002page01.cfm?chapt
er_no=visualization
Chapter 20: Global Winds
• Winds are named for
the direction from
which they blow, not
the direction they are
going.
• For instance, winds
blowing from the
Pacific Ocean toward
the coast of N.A. are
called westerly winds
because they blow
from West to East.
• its
Remember: they move
from high to low.
Good diagram on p. 88 of
Sovio Fig. 20.1
•
Because the earth turns on its axis, from west
to east, the two main factors in wind direction
are: A)rotation of earth on its axis B) Location
of High and Low Pressure Air masses.
• the winds in the northern hemisphere curve to
the right and in the south to the left.
• Air flows from an area of high pressure to an
area of low pressure.
• Continual trade winds, the northeast trades
and southeast trades blowing from subtropical, high pressure belts to the constant
low pressure region at the equator.
• At the equator, winds are
calmdoldrumsArea of continuous low
pressure! (popular provincial question)
Look at Fig. 20.2
The rotation of the earth on its axis is responsible
for the curving of winds, to the right in the
northern hemisphere and left in the southern
hemisphereknown as Coriolis Effect.
http://www.classzone.com/books/earth_science/terc/content/visualizations/es1904/es1
904page01.cfm?chapter_no=visualization
http://www.wiley.com/college/strahler/0471480533/animations/ch07_animations/
animation2.html
http://weather.about.com/od/weathertutorials/tp/coriolisvideos.htm
Wind Patterns
You also need to know which winds are found along latitudes:
• Equatorial : Doldrums = low pressure (constant) I ask why?
• 0-30 N/S North East and South East Trades
• 30-60 N/S Westerlies (affect B.C.—in the North provincial)
• 30 N and S known as Horse Latitudes (High
• Pressure)
• 60 degrees N/S (Low Pressure—not continuous)
• 60-90 N/S Easterlies
• 90 N/S High Pressure (Constant) therefore, very little or
not precipitation
Global Circulation Model
Global Atmospheric Circulation
Jet Stream
A stream of fast-moving, atmospheric air that occurs where the
troposphere meets the stratosphere
Meanders east at speeds of 300 km an hour
located in mid-latitudes they migrate north/south
Weather systems in the lower troposphere are greatly influenced by jet
streams. (bring cold air either south or northcreating bad weather
conditions.
Chinook Winds
• Are warm winds that blow down the leeward side of mountain
ranges especially the eastern slopes of the Rockies.
• The sinking air is warmed by compression at a rate of about
1 Celsius per 100 meters.
• Bring warm conditions to Calgary, Alb.
Land and Sea Breezes. (FIG
20.6)-very popular on the
provincial exam!
Land warms and cools much
faster than water creating
temperature and pressure
changes between these two
locations.
During the summer the land
heats rapidly after sunrise
and air in contact with the
ground also warms and
expands. As the warm
expanded air begins to
rise, cool dense air from
the ocean flows in to
replace itSea Breeze
Animation:
http://www.classzone.com/books/earth_science/terc/content/visualiz
ations/es1903/es1903page01.cfm?chapter_no=visualization
As night approaches the land cools rapidly and is now
cooler than the ocean. Air over the warmer ocean
begins to rise and the cooler air from the land
moves out to replace it resulting in a land breeze.
Valley and mountain breezes On hot summer day’s
valleys act as wind tunnels generating extremely
high winds in mountain passes. As the sun heats
the mountain slopes, air begins to rise and is
replaced by air rushing up the valley. The
narrower the valley the stronger the wind.
(opposite at night)
Local Wind Systems
Sea Breeze
Land Breeze
•Sun-heated air over land rises –
Low pressure
•Cooler air over water sinks –
High pressure
•Night air over land cools fast –
High pressure
•Air over water stays warmer –
Low pressure
Water Cycle (fig. 21.1)
Continual movement of water from the oceans into
the atmosphere, and back to earth (into the
ocean) again is referred to as the
water/hydrologic cycle.
Evaporation of water leaves behind
salt…therefore only freshwater is involved in
the cycle.
Most of the water comes from ocean, but we also
get evaporation from lakes/rives and
transpiration from vegetation.
When moist air rises, it cools, and the water
vapous condenses to form cloudswinds carry
clouds over the continent and some comes down
as snow or air.
Some infiltrates the ground (remember aquifers!)
the rest will runoff into rivers and lakes
returns water back to the ocean
Thing of three environmental issues that you have
heard about that would relate to the water
cycle?
http://www.sweetwater.org/ed
ucation/watercycle.swf
http://epa.gov/climatechange/k
ids/water_cycle_version2.html
Infiltration—water below ground
remember aquifers
Transpiration—evaporation of plants (release
of water vapour) aka evapotranspiratio
Condensation—gas to liquid
Evaporation—liquid to gas
Precipitation—result of condensation
the water reaching earth
Dew, Frost and clouds
Dew Point
Humidity amount of water vapour air contains
Absolute humidity refers to the amount of water vapour
present in a body of air.
Relative humudity is the percentage of water vapout in the air
100 % saturated then dew point has been reached and water
vapour begins to condense
Warmer air can hold more vapour before it saturates
Cold air is the oposite…some people say its too cold to snow and
that is true because the air can only hold very little water
Dew
Why is the lawn wet in the morning after a clear night?
Ground quickly loses much of the heat it gained during the day
and begins to cool the air in contact with it.
As air temperature drops, relative humidity continues to
increase until 100% saturated.
condensationresults in dew (below freezingfrost or ice)
FogWhen air close to earth is cooled enough that its dew point is reached,
water vapour begins to condense and forms a low lying cloud
Radiation Fog
Forms during cloudless/windless nights
seen in low lying valley bottoms as cooler dense air from the surrounding valley
where the air quickly reaches dew point and condensation occurs.
most common on land in late fall and winter
Advection Fog
Is produced as warm moist air cools to its dew point (saturation) while moving
over a cold surface (always involves horizontal movements of air)
Example—occurs along Pacific coast in the summer. Surface water is cooler
than air above-air reaches dew point and fog is formed.
Radiation Fog
Advection Fog