Transcript Atmospheric Pressure and Winds

Atmospheric Pressure and
Winds
Chapter 19
Air Pressure
• The weight of the atmosphere per unit
area.
– 1kg per cm² at sea level
– 14.7 lbs/in² at sea level
• Directed equally in all directions
• Barometer
– 76cm / 30in at sea level
– given in metric unit of millibars (mb)
Barometer
• Instrument that
measures air pressure
• Mercury Barometer
– Requires a tall column
of mercury
• Aneroid Barometer
– Uses no liquid
Mercury Barometer
Air Pressure Records
Why Air Pressure Changes
• Temperature Changes
– warm air is lighter than cold air
• Changing Humidity
– the more water vapor, the lighter the air
– water vapor pushes out heavier O2 and N2 of
the dry air
What Makes Wind Blow
• Pressure Gradient Force
– the difference in air pressures that cause
winds
• Local Winds
– Sea Breeze: daytime wind from sea, land
heats faster than water and causes air to rise
– Land Breeze: nighttime wind from land to
sea, water is warmer than land
Wind blows over tractor trailer
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Local Winds: Sea Breeze
Kite Flying
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Local Winds: Land Breeze
http://www.classzone.com/books/earth_science/terc/content/visualizations/es1903/es1903page01.cfm?chapter_no=visualization
Kite Flying
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Earth’s Rotation and Weather Systems
• Coriolis Effect
– Turns wind to the right
• Clockwise
– Out of HIGH pressure
• Counterclockwise
– Into LOW pressure
Coriolis Effect
http://www.classzone.com/books/earth_sci
ence/terc/content/visualizations/es1904/es
1904page01.cfm
High Pressure Center
Highs =
Anticyclones
Pressure
decreases as it
moves OUTward.
Pressure is HIGH
in the center.
Low Pressure Center
Lows = Cyclones
Pressures
decreases as air
moves INwards.
Pressure is LOW in
the center.
Produce Hurricanes
LOW
PRESSURE
Global Air Currents
• If the Earth is
not rotating, the
air currents would
flow from equator
to pole and back.
Circulation on Rotating Earth
• As Earth rotates the
two large air cells
break into small cells.
• Trade winds = two
belts of winds that
blow constantly from
east to west.
• Westerlies = two belts
that blow from west to
east.
• Polar Easterlies =
blow from polar high
to polar low.
Air Masses
• Huge section of air that
has the same weather
throughout
• Take on the
characteristics of the area
they originated over
• maritime tropical – mT
• continental tropical – cT
• maritime polar – mP
• continental polar - cP
Disc Ed: Earth Science for Students: Weather [26:06]
Air Mass Source Regions
Fronts
• Boundary between 2
air masses
• Causes warm air to
rise
– Where temperatures
and humidity change
Warm Front: Map View
• Slow moving
• Long lasting rain
• Cirrus to stratus
clouds, then
nimbostratus
Warm Front: Side View
Warm front animation
http://www.classzone.com/books/earth_science/terc/content/visualizations/es2002/es20
02page01.cfm?chapter_no=visualization
Warm Front: Side View
Cold Front: Map View
• Fast moving
• Unstable air
• Cumulus – cumulonimbus
clouds
• Thunderstorms
• Clears quickly and leaves
clear skies
Cold Front Animation
http://www.classzone.com/books/earth_science/terc/content/visualizations/es2002/es20
02page01.cfm?chapter_no=visualization
Features of a Weather Map
Key to Features
1 -- Cold Front
2 -- Warm Front
3 -- Stationary Front
4 -- Occluded Front
5 – Trough
6 -- Squall Line
7 -- Dry Line
8 -- Tropical Wave
Cold Front
Cold Front
Occluded Front: Map View
• When a cold front
overtakes a warm
front
• Form low pressure
systems
Occluded Front: Side View
EL NINO
• Warm countercurrents replace cold waters
with warm waters.
• La Nina – opposite of El Nino
http://www.splashvision.com/video/853_El-nino-education---complete-timelapse-explanation.html
Ch 20 Severe Storms
Thunderstorms
• Forms when warm, humid air rises in an unstable
environment.
• Three stages:
• Cumulus stage: updrafts supply moisture and grows cloud upward
• Mature stage: heavy rain, lightning, etc.; most active
• Dissipating stage: downdrafts dominate and cooling occurs,
HSW: Flash To Bang: Lightning Casualties Time: 03:49
HSW: Electricity: Lightning Time: 04:33
HSW: Lightning Time: 01:57
HSW: Flash To Bang: Lightning Safety Time: 02:59
Tornadoes
• Windstorm that is the form of a rotating column
(vortex).
• Tornado season: April – June
• Must develop a mesocyclone (vertical cylinder of
rotating air that develops in the updraft of a
thunderstorm)
• Page 573 Figure 18
HSW: Weather: Reading The Warning Signs Time: 01:48
Tornado: What We Know About Tornadoes Time: 04:50
Violent Storms: Tornadoes Time: 02:15
Storm Chasers: Tornado Aftermath Time: 03:59
Hurricanes
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Whirling tropical cyclones with winds 119 kph or more
Also called typhoons, cyclones, and tropical cyclones
Form between 5-20o latitude
Fueled by energy given off when huge amounts of
water vapor condense
Late summer – when oceans are warmer
Eyewall = doughnut shaped wall surrounding the eye.
Eye = center “hole” of the hurricane
Rainbands = parallel bands of clouds within the
hurricane that produce heavy rain.
Hurricane Structure
Hurricane Damage
• Storm Surge = dome of water about 6580 km wide that sweeps across the coast
where the hurricane eye moves onto land.
• Saffir-Simpson Hurricane Scale
• Pg 577 Table 2
PBS: Storm that Drowned a City
http://video.pbs.org/video/1218652893/
How To Survive: Storm Strike Time: 04:13