Transcript Atmospheric Circulation

Atmospheric Circulation
1. Global
Convection
Currents
• Equator =
warm 
rising air
• Poles =
cold 
sinking air
2. Global Winds
• Air travels from H (high) to L (low) pressure
• H-L Pressure Zones: Horse latitudes and Doldrums are
places where air flow slows and wind speed dies down
• Prevailing winds: Trade winds, Westerlies, and Polar
Easterlies are characterized by winds that travel in one
main direction (from HL)
• Hadley Cells cells of
atmospheric
convection
– Driven by
solar heating
– Air rises near
equator
– Air sinks near
the poles
3. Air Movement
• Convergence – L pressure
systems have a CCW rotation
causing it to rise and cool
inside
– Condenses
– Forms clouds
– Cause of “bad weather”
• Divergence – H pressure
systems have a CW rotation
causing air to sink
– Diverges
– Form clear air
– Cause of “good weather”
• Jet Streams –
form at
boundaries
between
convection cells
– Fast moving
ribbons of air in
the upper
atmosphere
4. Air Masses
• Air Masses – large
uniform volume of air
that has the same
– Density
– Temperature
– Humidity
4 types • Maritime Polar - mP
• Maritime Tropical - mT
• Continental Polar - CP
• Continental Tropical - cT
Weather Formation
5. Wind Formation
• Variations of solar energy
input lead to 
• temperature differences
which lead to 
• pressure variations in the
atmosphere
• The wind blows to try to
correct these imbalances
in pressure.
• Regions of L and H
pressure moving through
an area cause changes in
weather as different air
masses pass by.
6. Atmospheric
Stability
• Unstable air –
Temp of air mass >
Temp of
surrounding air =
rising air
• Stable air –
Temp of air mass <
Temp of
surrounding air =
sinking air
7. Weather Fronts
• Air Fronts –
boundaries where
2 different air
masses meet and
do not mix
– Caused by density
differences
– Causes changes in
elements of
weather
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Temperature
Dew Point
Wind Direction
Cloud Cover
Type of Weather
• 4 main types –
– Cold
– Warm
– Stationary
– Occluded
• Cold Front –
leading edge of
colder air that is
replacing warmer
air.
– Warm air rises
– Usually form with
areas of L
pressure
– Weather:
• Heavy rain
• Hail
• Strong winds
– Summer months:
thunderstorms
and severe storms
• Warm Front –
Leading edge of
warmer air that is
replacing cooler air.
– Warm air rises slowly
over colder air
– Weather:
• Clouds
• Gradual to
increasing rain
• Fog
• Clears and warm
after
– Winter months:
hazardous weather
conditions
• Sleet
• Freezing rain
• Stationary Front –
boundary between
2 different air
mass with
different densities
but neither is
advancing
– Air masses do
not move
together
– Weather:
• clear to partly
cloudy
• If a lot
moisture =
rain/storms
– Ice storms
– Flooding
• Occluded Front –
when a cold front
catches up to a
warm front
– Cold fronts move
much faster than
warm fronts
– Cold takes over
– Weather:
• Warm or cold
• Clear to partly
cloudy
• If a lot of moisture
= rain/storms
– Ice storms
– Flooding
– Thunderstorms
Types of Weather
8. Types of weather
• Sunny
– H pressure
•
Clouds
– Air is lifted and cooled
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Rain
Snow
Freezing Rain/Ice
– Freezing air near Earth’s surface
•
Hail
– Supercooled water drops grow like snowballs
•
Sleet
– Frozen rain drops (transparent)
•
Dust Storms
– Strong, dry cold front
•
Fog
– Stratus cloud on the ground
– Moist, warm front
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Hurricane
Lightning
– Discharge of electricity in the atmosphere
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Thunderstorm
Tornado
Wind
– Imbalance of heating in the atmosphere
9. Elements of Weather and
Weather Instruments
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Temperature  Thermometer
Wind Speed  Anemometer
Air Pressure  Barometer
Moisture  Hygrometer
• Precipitation  Rain Gauge or
Doppler Radar
• Cloud Cover  Satellite
Imaging
10. Severe Weather
• Severe weather
hazards –
dangerous
weather
phenomena that
threaten life and
property
• Thunderstorms –
caused by unstable
air masses
– Form
cumulonimbus
clouds
– Warm, moist air is
forced up rapidly by
fronts, mountains,
or daytime heating
• Tornadoes violently rotating
column of air
– Forms in a severe
thunderstorm called
a supercell
– Wind coming in
starts to swirl and
forms a funnel
– The spinning air
creates a L pressure
area
– Cold, dry polar air
meets warm, moist
tropical air
– Unstable conditions
exist
• Hurricanes – giant,
spiraling tropical
storms with high
wind speeds of 120
mph +
– Spiral towards L
pressure center
– Form over oceans
– Warm, moist air
rises rapidly
– The “eye of the
storm” is calm
• El Nino - a climate
pattern
representing an
unusual warming of
the eastern tropical
Pacific Ocean sea
surface
temperatures
– Trade winds weaken
– Warmer water in
the East
– Occur every 3-7
years
– Reduced upwelling
of deep nutrient
rich waters
• La Nina - a climate
pattern representing
a cooling of the
eastern tropical
Pacific Ocean sea
surface
temperatures
– Trade winds
strengthen
– Warmer water in
the West (normal)
– Usually occur after
an El Nino
– Enhanced upwelling
of deep nutrient
rich waters
Weather Maps
11. Weather Maps
• Weather maps – allow
meteorologists to
understand current
weather and predict
future weather
• Station Model – symbols
used to show weather
conditions
– Temperature
– Wind
• The wind barb (parts ff
and dd combined) is like
an arrow and points in
the direction the wind is
blowing.
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Weather
Dew point
Sky cover
Pressure
Pressure/Front Map
Temperature/Front Map