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The Earth-Atmosphere Energy Balance

The earth-atmosphere energy balance is the balance between incoming energy from the Sun and outgoing energy from the Earth. Energy released from the Sun is emitted as shortwave light and ultraviolet energy. When it reaches the Earth, some is reflected back to space by clouds, some is absorbed by the atmosphere, and some is absorbed at the Earth's surface.

Canned Heat

Overview

Different colored objects absorb energy at different rates. That is partially due to albedo. Albedo is the amount of reflection from a surface. The demonstration will show that water in a dark colored can will have a higher temperature after exposure to the sun than water in a shiny can.

Procedure

  1. Fill the two cans with about two inches of cold water.
  2. Measure the temperature of the water in each can. (The readings should be the same.)
  3. Remove the thermometer and place the cans in a sunny location where they will not be disturbed and receive two hours of sunlight.
  4. After two hours, measure and compare the water temperature in each can.

Discussion

The darker and duller an object, the more energy that object absorbs. The lighter colored or shiner an object, the less energy that its absorbs. But how does the water temperature change?

For some objects, like water and glass, light passes through with little direct heating effect. The water is heated by the energy absorbed then emitted by the cans. For white or shiny metallic surfaces, the energy isn't absorbed very quickly either, as some is reflected away. For a black material, light and heat are almost completely absorbed with little reflection.

Heated bodies also emit energy. The more energy an object absorbs, the more it radiates. The water in the white can was not as warm as in the black can because the white can absorbed less energy and therefore has less energy to radiate into the water. This type of radiation, where color affects the ammount of radiation absorbed, is called "black body radiation".

Live Weatherwise

Avoid the Heat

Stay out of the heat and indoors as much as possible. Spend time in an air conditioned space. Only two hours a day in an air-conditioned space can significantly reduce the risk of heat-related illness. Shopping Malls offer relief if your home is not air-conditioned.

If air conditioning is not available, stay on the lowest floor out of the sunshine. Remember, electric fans do not cool, they just blow hot air around.

Dress for the heat

Wear loose-fitting clothes that cover as much skin as possible. Lightweight, light-colored clothing reflects heat and sunlight and helps maintain normal body temperature.

Protect face and head by wearing a wide-brimmed hat. Avoid too much sunshine. Sunburn slows the skin's ability to cool itself. Use a sun screen lotion with a high SPF (sun protection factor) rating.

Do not drink IN the Heat

Drink plenty of water and natural juices, even if you don't feel thirsty. Even under moderately strenuous outdoor activity, the rate your body can absorb fluids is less than the rate it loses water due to perspiration.

However, if you have epilepsy or heart, kidney, or liver disease; are on fluid-restrictive diets; or have a problem with fluid retention, you should consult a doctor before increasing liquid intake.

Eat for the Heat

Eat small meals more often. Avoid foods that are high in protein because they increase metabolic heat. Avoid using salt tablets, unless directed to do so by a physician.

Living in the Heat

Slow down. Reduce, eliminate, or reschedule strenuous activities such as running, biking and lawn care work when it heats up. The best times for such activities are during early morning and late evening hours. Take cool baths or showers and use cool, wet towels.

 

However, since the Earth is much cooler than the Sun, its radiating energy is much weaker (long wavelength) infrared energy. We can indirectly see this energy radiate into the atmosphere as heat, rising from a hot road, creating shimmers on hot sunny days.

The earth-atmosphere energy balance is achieved as the energy received from the Sun balances the energy lost by the Earth back into space. In this way, the Earth maintains a stable average temperature and therefore a stable climate. Using 100 units of energy from the sun as a baseline the energy balance is as follows:

At the top of the atmosphere - Incoming energy from the sun balanced with outgoing energy from the earth.
Incoming energy Outgoing energy
Units Source Units Source
+100 Short wave radiation from the sun. -23 Short wave radiation reflected back to space by clouds.
    -7 Short wave radiation reflected to space by the earth's surface.
    -49 Longwave radiation from the atmosphere into space.
    -9 Longwave radiation from clouds into space.
    -12 Longwave radiation from the earth's surface into space.
+100 Total Incoming -100 Total Outgoing
The atmosphere itself - Energy into the atmosphere is balanced with outgoing energy from atmosphere.
Incoming energy Outgoing energy
Units Source Units Source
+19 Absorbed short wave radiation by gases in the atmosphere. -9 Long wave radiation emitted to space by clouds.
+4 Absorbed short wave radiation by clouds. -49 Long wave radiation emitted to space by gases in atmosphere.
+104 Absorbed longwave radiation from earth's surface. -98 Longwave radiation emitted to earth's surface by gases in atmosphere.
+5 From convective currents (rising air warms the atmosphere).    
+24 Condensation /Deposition of water vapor (heat is released into the atmosphere by process).    
+156 Total Incoming -156 Total Outgoing
At the earth's surface - Energy absorbed is balanced with the energy released.
Incoming energy Outgoing energy
Units Source Units Source
+47 Absorbed short wave radiation from the sun. -116 Long wave radiation emitted by the surface.
+98 Absorbed longwave radiation from gases in atmosphere. -5 Removal of heat by convection (rising warm air).
    -24 Heat required by the processes of evaporation and sublimation and therefore removed from the surface.
+145 Total Incoming -145 Total Outgoing

The absorption of infrared radiation trying to escape from the Earth back to space is particularly important to the global energy balance. Energy absorption by the atmosphere stores more energy near its surface than it would if there was no atmosphere.

The average surface temperature of the moon, which has no atmosphere, is 0F (-18C). By contrast, the average surface temperature of the Earth is 59F (15C). This heating effect is called the greenhouse effect.

 

How cloud cover can affect nighttime temperatures - Click to enlarge

 

Lesson 1
Lesson 2
Lesson 3
Lesson 4
Lesson 5

The Hydrologic Cycle

The basic hydrologic (water) cycle

The hydrologic cycle involves the continuous circulation of water in the Earth-Atmosphere system. At its core, the water cycle is the motion of the water from the ground to the atmosphere and back again. Of the many processes involved in the hydrologic cycle, the most important are...

  • evaporation
  • transpiration
  • condensation
  • precipitation
  • runoff

Evaporation

Evaporation is the change of state in a substance from a liquid to a gas. In meteorology, the substance we are concerned about the most is water.

For evaporation to take place, energy is required. The energy can come from any source: the sun, the atmosphere, the earth, or objects on the earth such as humans.

Everyone has experienced evaporation personally. When the body heats up due to the air temperature or through exercise, the body sweats, secreting water onto the skin.

The purpose is to cause the body to use its heat to evaporate the liquid, thereby removing heat and cooling the body. It is the same effect that can be seen when you step out of a shower or swimming pool. The coolness you feel is from the removing of bodily heat to evaporate the water on your skin.

Transpiration

Transpiration is the evaporation of water from plants through stomata. Stomata are small openings found on the underside of leaves that are connected to vascular plant tissues. In most plants, transpiration is a passive process largely controlled by the humidity of the atmosphere and the moisture content of the soil. Of the transpired water passing through a plant only 1% is used in the growth process of the plant. The remaining 99% is passed into the atmosphere.

 Leaf it to Me

Overview

There are two methods water moves from the ground to the atmosphere as part of the hydrologic cycle. Transpiration is basically evaporation of water from plant leaves. Studies have revealed that transpiration accounts for about 10% of the the moisture in the atmosphere, with oceans, seas, and other bodies of water (lakes, rivers, streams) providing nearly all of the remaining amount.

The student will observe the effect of transpiration as water is moved from the ground to the atmosphere.

Procedure

  1. Place a large plastic bag over a living limb of a tree or large bush. (The limb should not touch the ground.)
  2. Tie the open end of the bag around the tree or bush. Make sure there are no air leaks.
  3. At the closed end of the bag, tie a rock to the bag so the bag is weighted and forms a collection point for the water.
  4. After a predetermined time of your choosing (at least 2 hours after "bagging" the branch), poke a hole in the bag and collect and measure the water. Then remove the bag and rock from the branch.

Discussion

Plant transpiration is generally an invisible process as the water from the exiting the leaves evaporates quickly. The temperature inside the bag will increase with heating from the sun. However, the water vapor will condense back into water as it comes in contact with bag and begin to collect.

During a growing season, a leaf will transpire many times more water than its own weight. An acre of corn gives off about 3,000-4,000 gallons (11,400-15,100 liters) of water each day, and a large oak tree can transpire 40,000 gallons (151,000 liters) per year.

The amount of water that plants transpire varies greatly geographically and over time. There are a number of factors that determine transpiration rates:

  • Transpiration rates go up as the temperature goes up, especially during the growing season, when the air is warmer due to stronger sunlight and warmer air masses.
  • As the relative humidity of the air surrounding the plant rises the transpiration rate falls. It is easier for water to evaporate into dryer air than into more saturated air.
  • Increased movement of the air around a plant will result in a higher transpiration rate. If there is no wind, the air around the leaf may not move very much, raising the humidity of the air around the leaf. The moving air result that the more saturated air close to the leaf is replaced by drier air.
  • Plants transpire water at different rates. Some plants which grow in arid regions, such as cacti and succulents, transpire less water than other plants as a measure to conserve water.

While the water may have a bitter or harsh taste (depending on the type of tree or bush selected) it is safe to drink and can provide much needed drinking water in survival situations.

Live Weatherwise

Drink plenty of water and natural juices, even if you don't feel thirsty. Even under moderately strenuous outdoor activity, the rate your body can absorb fluids is less than the rate it loses water due to perspiration. However, if you have epilepsy or heart, kidney, or liver disease; are on fluid-restrictive diets; or have a problem with fluid retention should consult a doctor before increasing liquid intake.

During times of excessive heat stay indoors as much as possible. Spend time in an air conditioned space. Only two hours a day in an air-conditioned space can significantly reduce the risk of heat-related illness. Shopping Malls offer relief if your home is not air-conditioned. If air conditioning is not available, stay on the lowest floor out of the sunshine. Remember, electric fans do not cool, they just blow hot air around.

Wear loose-fitting clothes that cover as much skin as possible. Lightweight, light-colored clothing that reflects heat and sunlight and helps maintain normal body temperature. Protect face and head by wearing a wide-brimmed hat. Avoid too much sunshine. Sunburn slows the skin's ability to cool itself. Use a sun screen lotion with a high SPF rating.

 

Condensation

Condensation is the process whereby water vapor in the atmosphere is changed into a liquid state. In the atmosphere condensation may appear as clouds or dew. Condensation is the process whereby water appears on the side of an uninsulated cold drink can or bottle.

Condensation is not a matter of one particular temperature but of a difference between two temperatures; the air temperature and the dewpoint temperature. At its basic meaning, the dew point is the temperature where dew can form.

Actually, it is the temperature that, if the air is cool to that level, the air becomes saturated. Any additional cooling causes water vapor to condense. Foggy conditions often occur when air temperature and dew point are equal.

Condensation is the opposite of evaporation. Since water vapor has a higher energy level than that of liquid water, when condensation occurs, the excess energy in the form of heat energy is released. This release of heat aids in the formation of hurricanes.

Sweatin' to the Coldies

Overview

There are three states of matter; gas, liquid, and solid. Water in our atmosphere exists in these three states constantly. As the temperature of water vapor (a gas) decreases, it will reach the point at which it turns into a liquid (called the dew point or the point at which dew forms). This change of state from a gas to a liquid is called condensation.

Using some ice and a glass, the students will chill the glass to the point where water from the atmosphere will condense on the outside of the glass. This demonstrate the change of state of water vapor to liquid.

Procedure

  1. Fill the cups/jars with ice.
  2. Add cold water to the cups/jars.
  3. Let the cups/jar set for about 30 minutes.
  4. Observe the outside of the glass for condensation.

Discussion

Ask the students where the water on the outside of the glass came from. The answer is from the atmosphere. As the water vapor molecules came in contact with the cold side of the glass, the temperature lowered to the dew point, condensing into a liquid.

The amount of water on the side of the glass depends upon the humidity which is the ratio of dry air to moist air. The higher the humidity the more moisture that air contains. The greater the moisture, the greater the water that can condense.

Live Weatherwise

Flash floods are the deadliest natural disaster in the world. They are caused by stationary or slow-moving thunderstorms that produce heavy rain over a small area.

Hilly and mountainous areas are especially vulnerable to flash floods, where steep terrain and narrow canyons can funnel heavy rain into small creeks and dry ravines, turning them into raging walls of water. Even on the prairie, normally-dry draws and low spots can fill with rushing water during very heavy rain.

Take time to develop a flood safety plan-for home, work, or school, and wherever you spend time during the summer. The National Weather Service has additional information about flood safety and a brochure "Floods and Flash Floods...The Awesome Power".

Preparations at home and work:
  • Know the name of the county where you live and nearby rivers and streams. Keep a map so you know where storms that may cause flash flooding are.
  • Determine if you are in a flood-prone area. If you are, know where to go if the water starts to rise. Have an escape route if you have to leave quickly.
  • Make a safety kit containing: A flashlight and extra batteries, battery-powered weather radio receiver and commercial radio, extra food and water, first-aid supplies, canned food and a can opener, water (three gallons per person), extra clothing, and bedding. Don't forget special items for family members such as diapers, baby formula, prescription or essential medications, extra eyeglasses or hearing aids, and pet supplies.
  • Know how and when to shut off utilities: Electricity, gas, and water.
  • Seek sources for obtaining local warning information such as from cable TV or the NOAA Weather Radio.

Precipitation

Precipitation is the result when the tiny condensation particles grow too large, through collision and coalescence, for the rising air to support, and thus fall to the earth. Precipitation can be in the form of rain, hail, snow or sleet.

Precipitation is the primary way we receive fresh water on earth. On average, the world receives about 38" (980 mm) each year over both the oceans and land masses.

The Rain Man

Overview

What goes up, must come down. Precipitation is the most commonly seen aspect of the hydrologic cycle. Students will learn how the water cycle works using 3-D paper craft activity. The students will see a demonstration the concept of precipitation.

Procedure

  1. Add about two inches (5 cm) of hot water to the mayonnaise jar.
  2. Add the ice cubes to the sandwich bag and seal it.
  3. Place the sandwich bag over the mouth of the jar, allowing one end of the bag to form a tip inside of the jar. This will allow the condensed water to collect at one location.
  4. After a few minutes, the water (rain) will begin to drip from the sandwich bag, returning to the water.

Discussion

Water vapor will rise from the hot water and come into contact with the bag fill with ice. The ice will cause the water to condense forming drops which will drop back into the water.

Despite the sometimes excessive rainfall that occurs, only about 0.3% of all water on the earth is found in the atmosphere. And only a small fraction of that is seen as rain. Most of the water in the atmosphere is in the gas state called water vapor

So while the hydrologic cycle is essential for life due to the water it brings, the vast amount of water in the cycle is found in the oceans, lakes, and ground water.

Live Weatherwise

  • If a flash flood warning is issued, get to higher ground immediately! Follow evacuation instructions, but don't wait for them if you think you are in danger.
  • Do not drive across flooded roads or bridges-they may be washed out.
  • If your vehicle stalls in water, abandon it and get to higher ground. It takes only a foot or two of rapidly-moving water to sweep away a car.
  • Walking or playing around flood waters is dangerous; you can be knocked from your feet in water only six inches deep!

 

Runoff

An example of runoff

Runoff occurs when there is excessive precipitation and the ground is saturated (cannot absorb any more water). Rivers and lakes are results of runoff. There is some evaporation from runoff into the atmosphere but for the most part water in rivers and lakes returns to the oceans.

If runoff water flows into the lake only (with no outlet for water to flow out of the lake), then evaporation is the only means for water to return to the atmosphere. As water evaporates, impurities or salts are left behind. The result is the lake becomes salty as in the case of the Great Salt Lake in Utah or Dead Sea in Israel.

Evaporation of this runoff into the atmosphere begins the hydrologic cycle over again. Some of the water percolates into the soil and into the ground water only to be drawn into plants again for transpiration to take place.

Water, Water Everywhere

Overview

Water is the most abundant and important substance on Earth. It is essential to life and is a major component of all living things. There are approximately 336,000,000,000,000,000,000 gallons of water on the earth, existing in three states; solid, liquid and gas.

The sources for this water storage are the oceans, icecaps & glaciers, ground water, fresh-water lakes, inland seas, soil moisture, atmosphere, and rivers. The students will discover the different water ratios in the earth's total water supply.

Procedure

  1. Label beaker #1 "oceans" and fill it with 1000 ml of water.
  2. Label the following beakers: beaker #2 "glaciers & icecaps", beaker #3 "groundwater", beaker #4 "fresh-water lakes", beaker #5 "inland seas", beaker #6 "soil moisture", beaker #7 "atmosphere", and beaker #8 "rivers".
  3. Inform the students to assume the earth's total water supply has been reduced to 1000 ml as indicated in beaker #1.
  4. Ask the students how much water must be transferred from beaker #1 into each of the remaining beakers representing the portion of water in each section. Write their estimates on the chalk board.
  5. Transfer the following amounts of water FROM beaker #1 to each of the remaining beakers.
    1. Glaciers & icecaps - 21.4 ml
    2. Groundwater - 6.1 ml
    3. Fresh-water lakes - 0.09 ml (∼2 drops)
    4. Inland seas - 0.08 ml (1 drops)
    5. Soil moisture - 0.05 ml (one drop)
    6. Atmosphere - 0.01 ml (0.2 drop)
    7. Rivers - 0.001 ml (0.02 drop)

Obviously, the last two, atmosphere and river, will be nearly impossible to obtain. So, by adding no drops will help in the students understanding of how little water is in those two locations.

Discussion

The students will be surprised how little water is found in each of the remaining beakers. The vast majority of water is found in the oceans; approximately 97.2%. The following are the percentages for each water source:

Water Source Water volume
(cubic miles)
Total Water
(%)
Oceans 317,000,000 97.24    
Glaciers & icecaps 7,000,000 2.14    
Groundwater 2,000,000 0.61    
Fresh-water lakes 30,000 0.009  
Inland seas 25,000 0.008  
Soil moisture 16,000 0.005  
Atmosphere 3,100 0.001  
Rivers 300 0.0001
Total water volume 326,000,000 100.        

Despite the over abundance of rain we often receive, the atmosphere contains very little of the earth's total water supply. This demonstration can lead into water conservation awareness and to get the students to think about ways to save our drinking water. For more info visit EPA Water Sense

Live Weatherwise

Flash floods are the deadliest natural disaster in the world. They are caused by stationary or slow-moving thunderstorms that produce heavy rain over a small area.

Hilly and mountainous areas are especially vulnerable to flash floods, where steep terrain and narrow canyons can funnel heavy rain into small creeks and dry ravines, turning them into raging walls of water. Even on the prairie, normally-dry draws and low spots can fill with rushing water during very heavy rain.

Take time to develop a flood safety plan-for home, work, or school, and wherever you spend time during the summer. The National Weather Service has additional information about flood safety and a brochure "Floods and Flash Floods...The Awesome Power".

Preparations at home and work:
  • Know the name of the county where you live and nearby rivers and streams. Keep a map so you know where storms that may cause flash flooding are.
  • Determine if you are in a flood-prone area. If you are, know where to go if the water starts to rise. Have an escape route if you have to leave quickly.
  • Make a safety kit containing: A flashlight and extra batteries, battery-powered weather radio receiver and commercial radio, extra food and water, first-aid supplies, canned food and a can opener, water (three gallons per person), extra clothing, and bedding. Don't forget special items for family members such as diapers, baby formula, prescription or essential medications, extra eyeglasses or hearing aids, and pet supplies.
  • Know how and when to shut off utilities: Electricity, gas, and water.
  • Seek sources for obtaining local warning information such as from cable TV or the NOAA Weather Radio.

 

What a Cycle!

At its core, the hydrologic cycle is water, as a liquid or solid, changing into water vapor (a gas) and back into a liquid or solid. This change of state of water occurs in the atmosphere and between the earth's surface and atmosphere.

This basic cycle is seen almost daily around the world in the formation and dissipation of clouds. When a cloud develops it is water vapor becoming a liquid. Conversely, when a cloud dissipates, liquid water changes state back into a gas.

The Ocean's Role

On a global scale, nearly all of the water in the water cycle is in the oceans. The oceans hold 96.5% of the earth's water and because of their size it may take thousands of years for a water molecule to move from the ocean to the atmosphere. This is in spite of an average 45 inches (114 cm) of water that evaporates from the ocean each year. (An additional 1% of salty water is also found in saltwater lakes and saline groundwater.)

The highest rate of evaporation from the oceans occurs in winter for both the Northern and Southern Hemispheres. The location of greatest evaporation is found on the east coasts of continents. This is due primarily to winter storms that move off the east coasts of continents which tend to have strong winds. These winds help carry water vapor away from its source thereby allowing more evaporation to take place.

The other factor is the warm ocean currents that move pole-ward along the east coasts of continents. The cold winter-time air masses that move over the water allow for large differences in air and sea temperatures so evaporation is also large. Then, when these differences in air and sea temperatures are combined with strong winds it makes evaporation in these regions very efficient.

Yet, of all evaporation that occurs over the oceans, a little over 90% of the moisture falls directly back into the sea as precipitation. And after spending upwards of a few thousand years in the ocean, a water molecule, on average, will only spend about nine days in the atmosphere before returning to earth. This is a very simple water cycle!

But over land, the water cycle can become quite complicated. The remaining 10% of moisture is transported over land and falls as precipitation from where it can travel a myriad of paths. If the precipitation falls as snow, it can remain frozen for a day or two then melt and flow into a river. Or the snow can become compacted and be locked up in a glacier for centuries.

Some water may infiltrate the soil or percolate into the groundwater. While most groundwater returns to the ocean, some groundwater can bubble up to the surface as a spring and evaporate back into the atmosphere, flow into a river, or even be captured and bottled for human consumption.

But remember, of all the water on the earth only 2.5% is fresh water and nearly all of that fresh water is locked up in glaciers and groundwater. Perhaps surprisingly, the atmosphere only contains about one-thousandths percent of all water on the earth.

The distribution of fresh water and estimation of the time a water molecule remains in various features, can be seen in the table (below). The Water Cycle chart (above ) shows additional sub-cycles contained within the greater cycle. .

Estimate of global FRESH water distribution and length water remains confined.
Location Total
Water (%)
FRESH
Water (%)
Duration
Ice caps, Glaciers, & Permanent Snow 1.74 68.7 > 1000 years
Groundwater 0.76 30.1 ~300 years
Soil Moisture 0.001 0.05 ~280 days
Ground Ice & Permafrost 0.022 0.86  
Lakes 0.007 0.26 1-100 years
Atmosphere 0.001 0.04 9-10 days
Wetlands 0.0008 0.03  
Rivers 0.0002 0.006 12-20 days
Humans / Animals / Plants 0.0001 0.003