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Air Pressure and Wind. Air Pressure. Air Pressure – the weight of the gases in the atmosphere pushing on the surface of the Earth . Air Pressure. At sea level, standard air pressure is 14.7 lb/in 2 or 1013.2 mb or 29.92 in of Hg. The Weight Of The Atmosphere On Our Shoulders .

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Air pressure
Air Pressure

  • Air Pressure – the weight of the gases in the atmosphere pushing on the surface of the Earth.


Air pressure1
Air Pressure

  • At sea level, standard air pressure is 14.7 lb/in2 or 1013.2 mbor 29.92 in of Hg


The weight of the atmosphere on our shoulders
The Weight Of The Atmosphere On Our Shoulders

  • At sea level, the weight of the column of air above a person is about 9,800 newtons (2,200 pounds)!

  • This is equal to the weight of a small car.

  • Why aren’t we crushed by this pressure?



How does air pressure change with altitude
How does air pressure change with altitude?

  • Atmospheric pressure is a measurement of the force due to air molecules at a given altitude.

  • The pressure of the atmosphere decreases as altitude increases.


This plastic bottle was sealed at 14,000 feet on top of Mauna Kea, and was crushed by the increase in atmospheric pressure (at 9,000 feet and 1,000 feet) as it was brought down towards sea level.


The greatest change in air pressure occurs in the lower atmosphere
The greatest change in air pressure occurs in the Mauna Kea, and was crushed by the increase in atmospheric pressure (at 9,000 feet and 1,000 feet) as it was brought down towards sea level.lower atmosphere.


Why does air pressure change with altitude
Why does air pressure change with altitude? Mauna Kea, and was crushed by the increase in atmospheric pressure (at 9,000 feet and 1,000 feet) as it was brought down towards sea level.

  • Remember, air pressure is the weight of the atmosphere pushing down from above.

  • The higher you go in the atmosphere the smaller the column of air that is pushing down from above.


How is air pressure measured
How is air pressure measured? Mauna Kea, and was crushed by the increase in atmospheric pressure (at 9,000 feet and 1,000 feet) as it was brought down towards sea level.

Air pressure is measured with a Barometer

There are Two Types of Barometers:

Mercury Barometer

Aneroid Barometer


How does air pressure change with altitude1
How Does Air Pressure Change With Altitude? Mauna Kea, and was crushed by the increase in atmospheric pressure (at 9,000 feet and 1,000 feet) as it was brought down towards sea level.

  • In the following activity you will investigate how air pressure changes with altitude. You will also determine the air pressure at various altitudes above sea level.


Record average sea level pressures
Record & Average Sea-Level Pressures Mauna Kea, and was crushed by the increase in atmospheric pressure (at 9,000 feet and 1,000 feet) as it was brought down towards sea level.


  • Air pressure can be analyzed on a weather map using Mauna Kea, and was crushed by the increase in atmospheric pressure (at 9,000 feet and 1,000 feet) as it was brought down towards sea level.Isobars – lines that connect points of equal air pressure.

  • Each isobar differs in pressure by 4 millibars.


Isobars on a map are used to determine the location of pressure systems and act as a way to forecast weather.


Why does air pressure change
Why Does Air Pressure Change? pressure systems and act as a way to forecast weather.

  • So far we know the air pressure decreases with altitude because there are less air molecules pushing down from above.

  • It also changes with temperature & humidity.


A look at high an low pressure
A look at High an Low pressure pressure systems and act as a way to forecast weather.


Two types of pressure systems
Two types of Pressure Systems-- pressure systems and act as a way to forecast weather.


Characteristics of high and low pressures
Characteristics of High and Low Pressures pressure systems and act as a way to forecast weather.

  • Warm temperatures

  • Falling barometer

  • Poor weather

  • Air moves toward center- counterclockwise

  • Cool temperatures

  • Rising barometer

  • Fair weather

  • Air moves out from center - clockwise


Light Winds pressure systems and act as a way to forecast weather.

Strong Winds

  • Pressure Gradient – a change in pressure between two places. This creates a force that makes wind move from areas of high pressure to areas of low pressure


What causes wind pressure differences
What causes wind & pressure differences? pressure systems and act as a way to forecast weather.

Differential heating of land and water –

  • Differences in the heating of land and water creates different pressure systems.

  • Land heats up and cools off faster than water.

  • Land temperatures change quickly while sea temperatures change slowly.


On a local level this difference in heating creates breezes
On a local level, this difference in heating creates pressure systems and act as a way to forecast weather.breezes.

Sea Breeze


Sea breeze
Sea Breeze pressure systems and act as a way to forecast weather.


On a local level this difference in heating creates breezes1
On a local level, this difference in heating creates pressure systems and act as a way to forecast weather.breezes.

Land Breeze

Sea/land breeze animation


Valley Breeze pressure systems and act as a way to forecast weather.

Mountain Breeze


Why are the winds arrows drawn in a curved path and not in a straight line
Why are pressure systems and act as a way to forecast weather.the winds (arrows) drawn in a curved path and not in a straight line?


Wind and water appear to travel in curved paths because of the coriolis effect
Wind and water appear to travel in curved paths because of the CORIOLIS EFFECT.

  • Caused by the rotation of the Earth.

  • Wind and water are deflected to the right in the Northern Hemisphere

  • to the left in the Southern Hemisphere

[Coriolis Effect animation]


The rotation of the Earth also causes the rotation that is seen with tornadoes and hurricanes

[Tornado video]

[Hurricane Katrina]


How do we measure wind speed and wind direction
How do we measure wind speed and wind direction? seen with tornadoes and hurricanes

Anemometer- measures wind speed

Wind Vane – measures wind direction


Global Pressure Belts are caused by the seen with tornadoes and hurricanesuneven heating of the Earth which results in High and Low Pressure areas


90º N seen with tornadoes and hurricanes

Polar High

Subpolar Low

60º N

Subtropical High (Horse Latitudes)

30º N

Equatorial Low (Doldrums or ITCZ)

Subtropical High (Horse Latitudes)

30º S

Subpolar Low

60º S

Polar High

90º S


The global winds are the result of air moving from high pressure belts to low pressure belts
The Global Winds are the result of air moving from high pressure belts to low pressure belts.

  • Air always moves from high to low Pressure.

  • Winds are named for the direction they are coming from.


90º N pressure belts to low pressure belts.

Polar Northeasterlies

60 º

Prevailing Southwesterlies

30 º

Northeast Trade Winds

0 º

Southeast Trade Winds

30 º

Prevailing Northwesterlies

60 º

Polar Southeasteries

90º S


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