Winds and Pressure Systems - CRHS
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Transcript Winds and Pressure Systems - CRHS
What is pressure?
Pressure is accumulative force of gas
particles
http://www.falstad.com/gas/
High Energy gas (HOT) has lots of
movement, therefore high pressure
Low Energy (COLD) has less pressure
How do we measure pressure?
Using a Barometer
The height of the
Mercury Column is
equal to the
pressure acting on
the surface of the
mercury
P = gh
P = (density)(gravity)(height)
Two Types of Pressure Systems Occur in
Nature
Low Pressure Systems - “Cyclones”
High Pressure Systems - “Anti-Cyclones”
Each type has specific characteristics related
to the behavior of the gases that make up the
system and how they interact with each other
High Pressure Systems “Anti-Cyclones”
Winds blow outward
and clockwise at
surface
Associated with
converging winds
higher in the
atmosphere
Weather: clear and
“fair”
Low Pressure Systems
Winds blow inward and
counterclockwise at
surface
Associated with
diverging winds higher
in the atmosphere
Weather: cloudy with
precipitation (rising air)
What is Wind?
Wind is the movement of Air
Wind forms as a result of three factors:
Pressure Gradient Force
Coriolis Effect
Friction with the Earth’s Surface:
Pressure Gradients
Air wants to move from high to low pressure
(greater pressure difference = higher speed)
Isobars = lines of equal pressure
Coriolis Effect: Same effect as for ocean
currents
Moving air (wind) is deflected to the right of
intended path
Creates rotational movement
Friction with the Earth’s Surface
As air moves across the Earth’s surface, it is
slowed by contact with features of the Earth’s
surface
This slows down surface level winds, but
also creates mixing because higher level
winds continue at higher velocities
Wind is measured using two devices
SPEED is measured using an
ANEMOMETER
DIRECTION is measured using a WEATHER
VANE
• Local Winds are caused by temperature
differences.
• Two common types include :Sea and Land
Breezes: Occur in coastal areas
• Sea Breeze
• During the day, the land warms up
because of the sun. Air rises over the
land.
• To replace this air, cooler air from the
sea flows towards the land (sea
breeze)
Sea and Land Breezes (cont’d)
• Land Breeze
• During the night, the ocean is warmer than
the land. Air rises over the ocean.
• To replace this air, cooler air from the land
flows towards the sea (land breeze)
Day = Sea Breeze
Night = Land Breeze
• Mountain and Valley Breezes
• Valley Breeze: During the DAY air on the
slopes of mountains heats up and moves
up the mountain slope
• Mountain Breeze: At NIGHT air near the
mountain top cools more quickly than air
lower down, so it flows down slope
towards the valley
Valley Breezes
Mountain Breezes