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Atmospheric Pressure
Ch. 5
The Basics…
1. The atmosphere has weight (14.7 lb/sq in.)
2. We don’t notice b/c we have air and water
inside us (blood, tissue, and cells) exerting
outward pressure
3. Variations in pres. w/in Earth-Atmos system
causes atmospheric circulation = weather
and climate
Measuring Pressure
1. Mercury Barometer
•
•
Hear in inches…but really
measure in millibars
Avg @ sea lvl = 1013.2 millibars
2. Temp differences influence
patterns of high and low
pressure
Variations in Atmos Pressure
1. Vertical
•
Height,
pressure
2. Horizontal
•
•
Thermal (temp) – during the day air…
heats
expands
decreases in density
rises.
Less air at surface = L pressure
Dynamic (mvmt of Earth) - @ equator, air rises,
moves to poles. B/c of rotation air is pulled eastward
Basic Pressure Systems
1. Low (cyclone) L
•
•
Converging air circulation
Air ascending, lowering the pressure on the surface
L
2. High (anticyclone) H
•
•
Descending air circulation
Air blows down and away, increasing
the surface pressure
H
Wind Essentials
• The horizontal motion
of air across the Earth’s
surface
• Produced by differences
in air pressure from one
place to another
• Two principle
properties: direction
and speed
Driving Forces of Wind
• Gravity
• Pressure
Gradient Force
• Coriolis Force
• Friction Force
Gravity
• Gravity compresses the
atmosphere
• Causes the atmosphere
to be more dense at
lower altitudes.
• Gravity creates
atmospheric pressure
Pressure Gradient Force
• Drives air from areas of
higher pressure to
lower pressure.
• Without this force,
there would be no
wind.
• Pressure differences
are portrayed on maps
by isobars.
Coriolis Force
• Anything that flies or flows across the Earth’s
surface is deflected from a straight path by the
Coriolis Force.
• The deflection is caused by the Earth’s
rotation.
• This deflection occurs regardless of the
direction in which something is moving.
Coriolis Force
Friction Force
• Drags on the wind as it
moves across the
surfaces.
• The effect of this force
decreases with height
above the surface.
• Without friction, winds
would move at very
high rates of speed.
Small Group Work
LOCAL AND GLOBAL WINDS
1.
2.
3.
4.
5.
Land Breeze – Sea Breeze
Mountain Breeze – Valley Breeze
Drainage Winds
Chinook-type Winds
Monsoons
Global Wind Pressures
Review – Air Pressure:
• Differences in air pressure are created by the
unequal heating of Earth’s surface
– Warm, less dense air rises → L
– Cool, denser air sinks → H
• This circular patterns is know as the
convection current
Review – Wind:
• Differences in air pressure create moving air =
wind
• Winds usually travel from areas of H to L
• Two types of wind: local and global
– Local (influenced by geography):
•
•
•
•
•
Land Breeze – Sea Breeze
Mountain Breeze – Valley Breeze
Drainage Winds
Chinook-type Winds
Monsoons
Global Wind Pattern
•
•
•
•
Aka “general circulation” of upper atmospher
Move across the Earth in specific directions
Polar Easterlies: From 60-90 degrees latitude.
Prevailing Westerlies: From 30-60 degrees
latitude (aka Westerlies).
• Tropical Easterlies: From 0-30 degrees latitude
(aka Trade Winds).
Theoretical Model
Seasonal Variations
• January = Air over land cools more quickly,
therefore there is H pressure over landmasses
•
•
•
•
over Asia = Siberian High
over North America = Canadian high
over the North Atlantic = Icelandic Low
over the North Pacific = Aleutian Low
– Air moves towards to Lows, resulting in unstable
weather (winter storms)
• July = lengthy heating of the oceans reverses
pressure systems
• Pacific = Pacific High
• Atlantic Ocean = Bermuda High (N. Am), Azores High (Euro)
You Tube Clips
GLOBAL WIND PATTERNS
FINDING NEMO TURTLES