The Water Cycle

The water on Earth is limited

• It goes through a cycle that changes its form and location, but no new water is created. We drink the same water the dinosaurs did!

The cycle

• There are 4 parts to the water cycle, and we can start the cycle at any point, then follow the cycle through.

• Can you name the 4 parts?

The 4 parts of the water cycle are:

• Evaporation/Transpiration

• Condensation

• Precipitation

• Accumulation

What powers the Water Cycle?

• The Sun

• How?

The Sun transfers its heat energy to the

water on Earth, which causes evaporation. • What is evaporation?

A change of a liquid to a gas—when water evaporates from the Earth’s surface, it enters our atmosphere.

ALSO…

• Another form of transferring water to the atmosphere is called transpiration.

• This is similar to evaporation, but it comes from plants and trees.

• Think of it like a plant that is sweating, and the plant “sweat” (water) evaporates.

Transpiration

• Transpiration is the transfer of water vapor from plants to the atmosphere

I said the Sun transfers it’s Heat Energy to the water, what is meant by heat energy?

• Heat is a form of energy which causes molecules to move faster and spread out.

• There are three main ways to transfer heat…can you name any?

Heat Transfer

• The three methods of heat transfer are

1. Radiation

2. Conduction

3. Convection

Radiation

• This can best be described as the warm feeling you get from the Sun, or by sitting next to a fire.

• The heat is radiating out, and you feel it’s energy warming you.

Conduction

• This is the actual transfer of heat through contact.

• Some examples would be

1. Touching a hot plate

2. Walking barefoot on the sand at the beach and burning your feet

3. Can you think of one?

Convection

• Convection is the transfer of heat by the flow of material.

• Examples of convection heat transfer are

1. Using a blow-dryer

2. Heating a bowl of soup

So now we know the Sun powers the water cycle…what is next?

• Well, after evaporation and transpiration we have condensation, followed by precipitation, and accumulation, then the cycle continues.

Sun’s Heat Energy

Condensation

• Condensation is when water vapor (or gas) changes back to a liquid.

• This happens when the water vapor in our atmosphere cools enough to form droplets.

• This is how clouds form. We will discuss this more in-depth later.

After condensation, we have precipitation; can you figure out what precipitation is?

• CORRECT!!!

• As the water droplets combine and get

bigger and bigger they fall back to Earth and accumulate to complete the cycle.

• Precipitation can be in one of four forms; can you name them?

Atmospheric Conditions

• The type of precipitation we have depends on the atmospheric conditions in a particular place.

• To understand this, we must first understand our Atmosphere; we will talk about this soon.

After precipitation is Accumulation

• This is simply the water coming back to Earth’s surface and accumulating in the form of ice caps, rivers, lakes and oceans.

To recap the water cycle• There are 4 main parts to the water cycle,

but remember there is no particular order.

• Let’s name and describe each one.

• Evaporation/Transpiration, Condensation, Precipitation, and Accumulation.

http://antwrp.gsfc.nasa.gov/apod/image/earth_1_apollo17_big.gif

Earth’s Atmosphere

• Divided into 5 main layers

1. Troposphere

2. Stratosphere (contains Ozone Layer)

3. Mesosphere

4. Thermosphere

5. Exosphere

(Ozone Layer is within the stratosphere)

10km

50km

85km

500km

Ozone Layer

Troposphere

• Lowest layer of the atmosphere —we live here. Extends about 10km high

• Contains 75% of the atmospheric gas—Our atmospheric gas is mostly Nitrogen (78%) and Oxygen (21%).

• Contains 99% of water vapor

• Clouds, rain, and snow form here.

Stratosphere

• Layer above troposphere—between 10km and 50km high.

• Ozone layer exists here. Protects Earth from Sun’s harmful rays.

• An Ozone molecule is 3 oxygen atoms.

Mesosphere

• Layer above stratosphere—between 50km and 85km high.

• This is the “middle” layer of the atmosphere.

• Meteors are seen in this layer

Thermosphere

• Layer above mesosphere—between 85km and 500km high.

• Thickest layer of atmosphere.

• Named for it’s high temperatures.

Exosphere

• Outer most layer of the atmosphere—between 500km and 9000km.

• Most satellites are in this section.

• This last layer is just before “outer space.”

Temperature changes with height in atmosphere

Temperature changes

• Troposphere—decreases with height because air is thinner and absorbs less heat.

• Stratosphere—increases with height because ozone layer traps most of Suns energy.

• Mesosphere—decreases with height because very few molecules to trap heat (similar to our troposphere)

Temperature changes cont.

• Thermosphere and Exosphere—increases with height because it absorbs high amounts of Sun’s radiation (closest to Sun).

Any questions??

• Now that we know about our atmosphere,

We will concentrate more on the layer that we live in… we call this the

• Troposphere

Water cycle and our troposphere

• Does the temperature increase or decrease with height in our troposphere?

• So, when dealing with water, where would you expect to see frozen water, up high or down low?

• What are some names for frozen water?

1. Ice

2. snow

If temperature decreases with height

• Why isn’t all precipitation hail, sleet, or snow?

Let’s discuss this…understand the question, think, then raise your hand to answer.