The Water Cycle

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http://www.rspb.org.uk/Images/water_cycle_diagram_tcm9-50384.jpg

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By jazzmatazz9

Evaporation• Evaporation is the process by which water changes from its liquid form

to its gaseous form. This occurs when the Sun heats water. • Heating of the water causes the molecules to move faster. Some of

these molecules move so fast that they break free from the rest of the water molecules. These water molecules are now in the form of water vapor.

• Water vapor comes from mostly oceans. The oceans give us about 90% of the water vapor currently present in the air.

For those of you who do not know, this is a geyser. You can see some steam curling off of the superheated water. You’d probably think that steam is water vapor, right? WRONG! Steam is not water vapor. It is just water droplets in the air. True water vapor is invisible.

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Condensation

• Condensation is when liquid water forms from water vapor; it occurs when moist air reaches what is called its dewpoint and comes into contact with condensation nuclei or a solid surface.

• The air can only hold so much water vapor. The amount of water in the air is directly linked to the temperature of the air. As the temperature rises, the amount of water vapor the air can hold rises as well. The temperature at which the air can no longer hold any more vapor is called the saturation point.

• When the air reaches its saturation point, the water vapor will begin to condense (become a liquid). The dewpoint is the temperature at which the water vapor will begin to condense. When this happens at ground level, the water molecules stick together on surfaces, forming what we call dew.

Both dew and clouds are formed by condensation. The water vapor condenses on cool surfaces, and small water droplets form. The only difference between the two is that dew forms near the ground, while clouds form up in the air.

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Precipitation• Precipitation occurs when some of the components which make up a cloud (ice crystals or water

droplets) become too large, therefore too heavy to stay in the air and fall to the ground.This can happen because of two processes.

• The first process that causes precipitation to occur is called coalescence. This process usually occurs in moist cumuliform clouds where the air temperature is above freezing. See, the droplets are only sustained in the air because they are small enough to be held in the air by rising air currents and air resistance. The turbulence within the cloud may cause the water droplets to bump into each other and join to make a bigger one. These droplets will bump into each other, and soon these water droplets will be heavy enough to fall. The droplets fall, and they may still bump into each other and join in midair.

• The second process, the Bergeron-Findeisen process, requires ice crystals. Supercooled water droplets and ice crystals have different saturation points. When both of them exist in a cloud, water molecules will be transferred to the ice crystals from the supercooled water droplets. The ice crystals will grow because of this, and will soon fall when they are large enough. When falling, they will usually grow even more because of coalescence.

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Many of you have heard of this expression: “It’s raining cats and dogs!” Cats and dogs aren’t a form of precipitation, but it is used to express the fact that it is raining quite heavily and noisily. The second picture is a mystery, but I believe that it is raining frogs! As I said, these animals aren’t a form of precipitation. Rain, snow, and hail are, though.

http://larryfire.files.wordpress.com/2008/12/raining-cats-dogs-776852.jpghttp://blogdamanuca.files.wordpress.com/2009/03/raining_frogs.jpg

Snow• Snow is a common sight during the winter months in Europe and North America. It is

basically just ice crystals which have joined in a cloud and fallen through cold air.• Snow starts out as ice crystals which have formed a cloud when water vapor has

frozen around very small particles in the middle and upper layers of the atmosphere. The temperatures here are below 32 degrees Fahrenheit. These ice crystals will eventually bond, forming what we call snowflakes. These snowflakes fall to the ground once they are heavy enough.

• Snow that falls from the cloud often melts on its journey to Earth. It then reaches us as rain. However, we must not forget that thermal energy is required for a phase change. The thermal energy is absorbed from the surrounding air in the case of snow. This causes the air temperature to drop, so I believe that sometimes the snow will be frozen again, or at least partially frozen.

We can see plenty of snow here. The sky is cloudy, so snow could still fall. Then, ice crystals will fall from the sky, and start to melt. The air will cool down because its thermal energy has been absorbed, and the snow/rain will become snow again. http://www.yoopersteez.com/wordpress/wp-

content/uploads/2009/04/april-snowstorm-2.jpg

Rain

• Rain is a form of precipitation which reaches the Earth in liquid form. Rain usually forms in a cloud as either ice crystals or water droplets.

• The ice crystals/water droplets then become large enough to fall from the cloud. The ice crystals will usually melt on the way to Earth. This results in what we know as rain.

• Occasionally, the ice crystals/water droplets start to fall to the ground, but then evaporate in mid-air. This phenomenon is called virga. It occurs when there is a shallow layer of extremely dry air or a deep layer of dry air beneath the cloud. The effect that virga creates resembles a dark fringe beneath the cloud base.

This is one of those pictures which shows a ripple made by a raindrop. It’s pretty cool, if you’re a person who admires this. Here’s a silly question to think about: see that little drop of water above the ripple? Is it rain, or is it some water from the splash made by the rain?

http://blogs.wvgazette.com/johnmccoy/files/2009/11/rain.jpg

Hail• Hail is created when supercooled water droplets have been circulated through a

cumulonimbus cloud. The updraft area of a cumulonimbus cloud, that is.• As the water droplets pass through areas of the cumulonimbus cloud that have

different temperature and humidity, different types of ice build up on them. The layers of ice that form on them can be either clear or opaque. Clear ice forms on the droplets when there are many supercooled water droplets and the temperature is just below zero. In colder parts of the cloud, where the water droplets are smaller and fewer, the freezing is quite rapid. Bubbles of air are trapped, so opaque rime ice is formed.

• Hailstones are usually the size of a pea. However, we all know that there are exceptions. Some hailstones can grow to the size of golf balls, even oranges! The number of layers and the size depends on how long the hailstone remained in the storm. There have been hailstones with 25 layers of ice.

Interesting but weird facts time! Today, we shall be talking about horrible hailstorms. One such hailstorm was a hailstorm in northern India. In 1888, there was a hailstorm with hail the size of baseballs! Also, a hailstorm in Bangladesh (during the year of 1986) had hail which weighed about two-and-a-half pounds!

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Surface Runoff

• Any water (rain, snowmelt, etc.) that flows over land is called surface runoff. When this form of water hits land, it starts to flow downhill.

• In the wild, the water will start to flow downhill in channels. It will then move into larger creeks, then streams, then rivers. It will probably flow into the ocean.

• Precipitation and surface runoff are related. The interaction between these two is based on a location’s geography and time. Storms in the Amazon jungle and the United States will have different surface runoff effects, even if the storms are similar. Also, only one-third of precipitation runs into streams, rivers, and oceans. The other two-thirds either transpires, soaks into groundwater, or evaporates.

This is surface runoff. We can see the precipitation which hasn’t leaked into the ground (although it is leaking into a sewer. As I said before, surface runoff is impacted by a location’s geography and time.

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Transpiration• Transpiration is the way plants eliminate water. The leaves eliminate the water drawn

through their bodies. See, the plants only use a small amount of the water they absorb with their roots. The unnecessary water is released (in its gaseous form, water vapor) through the stomata.

• The result of transpiration is some saturated air covering the surfaces of the leaves. When the temperature falls, dew forms because the saturated air has reached its dewpoint.

• Transpiration gives us about 10% of the moisture found in the atmosphere. Evapotranspiration is actually both transpiration and evaporation. It is when the soil loses water because of evaporation and transpiration.

You can see some water droplets on this plant. This, I believe, is caused by transpiration. If I am correct, the saturated air has reached its dewpoint. I believe that the air has condensed, forming these water droplets on this blade of grass. http://community.seas.columbia.edu/weatherstation/glo/images/

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Accumulation

• Accumulation is when water collects in large bodies, such as oceans, seas, and lakes.

• The dictionary (www.dictionary.com) states that “accumulating” means “to gather into a heap, mass, cover, etc.;form a steadily increasing quantity.”

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Here, we can see a lake. A rather nice lake, actually. This is accumulation because water has collected in a large body. The large body of water is a lake, in this case.

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Percolation• Believe it or not, percolation may actually help your plants grow (if you have any). It

is when the Earth’s soil absorbs precipitation.• The water trickles into the ground through tiny spaces within the soil. It will eventually

gather above an impermeable rock layer. This water and soil (saturated) above the impermeable rock layer is called ground water. Underground “rivers” help the ground water move to depressions and lower elevations. The water table is the top level of the ground water.

• Different types of soil absorb water differently. Some soils may absorb water very nicely, while some may not absorb water at all. When water isn’t absorbed, surface runoff forms.

Here, we can see percolation. It may not be 100% natural, but it is almost the same. There is water underground. This water is seeping through the soil, or the rock, in this case. I’m not sure if it will come to an impermeable rock layer, though.

http://www.floridasprings.org/anatomy/jow/text/assets/08_percolation_thmb.jpg

Resources• http://science.howstuffworks.com/leaves-info5.htm• http://images.google.com/imgres?imgurl=http://community.seas.columbia.edu/

weatherstation/glo/images/transpiration.jpg&imgrefurl=http://community.seas.columbia.edu/weatherstation/fuse.php%3Fid%3D15&usg=__02ueaBU3dZYPCyWJnfzZX8Kt7RI=&h=282&w=425&sz=140&hl=en&start=8&um=1&itbs=1&tbnid=ZqmIA2DgwoNNyM:&tbnh=84&tbnw=126&prev=/images%3Fq%3Dtranspiration%26um%3D1%26hl%3Den%26safe%3Dactive%26gl%3Dus%26tbs%3Disch:1

• http://wpcontent.answers.com/wikipedia/commons/thumb/b/b0/Runoff.jpg/190px-Runoff.jpg

• http://www.cartage.org.lb/en/themes/sciences/earthscience/geology/WaterCycles/Hydrologicwater/BackgroundInformation/BackgroundInformation.htm

• http://www.floridasprings.org/anatomy/jow/text/assets/08_percolation_thmb.jpg• http://www.enchantedlearning.com/geology/label/watercycle/• http://ga.water.usgs.gov/edu/watercycletranspiration.html• http://ga.water.usgs.gov/edu/watercycleevapotranspiration.html• http://www.merriam-webster.com/dictionary/evapotranspiration• http://www.sciencedaily.com/articles/s/surface_runoff.htm• http://dictionary.reference.com/browse/accumulating

Resources cont.• http://ga.water.usgs.gov/edu/watercyclerunoff.html

• http://www.cartage.org.lb/en/themes/sciences/earthscience/geology/WaterCycles/Hydrologicwater/BackgroundInformation/BackgroundInformation.htm

• A Guide To Weather

By William J. Burroughs, Bob Crowder, Ted Roberson, Eleanor Vallier-Talbot, and Richard Whitaker