Water and wind
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Water and Wind. Chapter 22.2. http:// planetgreen.discovery.com/videos/blue-august-acid-in-the-water.html. Objectives. By the end of this section you will be able to… Discuss what happens to water in the troposphere What is air pressure and what is it also known as Explain what causes wind.

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Water and Wind

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Water and Wind

Chapter 22.2



By the end of this section you will be able to…

Discuss what happens to water in the troposphere

What is air pressure and what is it also known as

Explain what causes wind

Key Terms

Water cycle, transpiration, precipitation, humidity, dew point, Coriolis effect

Water is continually being moved throughout the troposphere

The water cycle outlines this movement

See page 781 in your book

The sun’s energy strikes the oceans (or any body of water for that matter) allowing them to escape into the air

This process is known as evaporation


Evaporated water condenses to form precipitation

During transpiration plants lose moisture through their porous leaves

These amounts can be immense a 1Km2 cornfield can transpire 900,000 gallons of water per day

The water in the atmosphere rises until it will cool enough to condense into droplets of liquid water (clouds)

As clouds cool and condense they can sometimes release moisture in the form of precipitation

The Fates of Precipitation

It remains on the ground until it evaporates again

It will flow into a larger body (Stream, sewer, lake, ocean etc.)

It will be absorbed and become groundwater

It can contribute to a snow/ice pack

Air contains different amounts of water vapor

As temperatures drop the ability for air to hold water diminishes (air is drier)

At higher temperatures more water can be held by air (air is moist)

Humidity is the amount of moisture in the air

Relative humidity is a ratio, or a comparison between the amount of water the air can hold and the amount it is currently holding

This is usually given as a percentage

A hygrometer measures relative humidity

Water vapor becomes liquid at its dew point

This is the point at which the rate of condensation equals the rate of evaporation

So why do drops of water form on a cool glass of lemonade during a warm summer day?

Clouds are made up of small water droplets or at higher altitudes, ice crystals

Where clouds form can determine their shape and characteristics

The root words cirrus, stratus, and cumulus are applied to cloud types in order to describe them

Cirrus clouds are thin and wispy and occur at high altitudes

Stratus clouds are layered and look like blankets

Cumulous clouds are white and fluffy and usually have flat bottoms

See page 783


Cloud names can be combined or have a prefix or suffix added to them

The prefix nimbo- or the suffix –nimbus implies that particular cloud will produce precipitation

Mercury barometers indicate air pressure by using a column of mercury (Hg)

This is why atmospheric pressure is sometimes referred to as mm of mercury

Average barometric pressure is around 760 mm of Hg

Pressure can also be measured by the unit atmosphere. 1atm = 760 mm Hg

The pascal (Pa) or torr is also used

Aneroid barometers do not contain liquid

These types of barometers contain a vacuum chamber which will move a lever on a spindle

Why is one better than the other?

What causes wind?

Pressure gradients (or differences) are what causes air to move

Much like the window in your car

Or more dramatically the window of an airplane

What causes pressure gradients on Earth?

The Sun! ….see demo

Wind always moves from areas of high pressure to areas of low pressure

You can see these on weather maps

Isobars are areas of pressure that are the same.

Each line represents an area of consistent pressure

See weather map

Directions of wind are also affected by the Earth’s rotation

The Coriolis effect is the curving of the path of a moving object from an otherwise straight path, because of the Earth’s rotation


So why does the Coriolis effect occur?

Its physics!

Depending where you are located on the Earth will dictate the speed you are traveling (even if you’re standing still)

Someone standing on the equator has to travel faster than someone standing on the north pole (demo?)

The Coriolis effect and isobars can allow us to make predictions on wind and weather patterns

These regions are known as wind belts

Each hemisphere (N&S) have 3

These paths are so predictable we can use them to travel

Homework page 787 1-6

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