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Rain Shadows and Sea Breezes

Part One from: http://www.geosociety.org/educate/LessonPlans/Land-WaterTemp_Lab.pdf (You will need Adobe Reader to view document)
Part Two from: USGS
http://interactive2.usgs.gov/learningweb/teachers/volcanoes_lesson3_2.htm
Modified by: Kirstin Bittel
Edited By: Stephanie Nardei

   

Time:
2 periods
Preparation Time:
5 minutes making copies
Materials:
Part One
Light colored sand
Dark colored sand
Water
Thermometers
Lamps with high wattage bulbs
Part Two
Map of Oregon
Average Rainfall Handout

Abstract
Where toxicants of environmental health importance are transported through the air, understanding the natural processes, which contribute to air movement and weather patterns of a region, is important. For example in some cities inversion layers trap pollutants close to the ground. Students will use maps to analyze rainfall data from an area of Oregon and temperature data from a simulation of land to sea to develop an understanding of adiabatic cooling, rain shadows and sea breezes. They will then propose the impacts these weather processes could have on environmental health issues.

Objectives
Students will be able to:
1. Plot the average rainfall for a variety of cities on a U.S. map.
2. Use results to determine patterns.
3. Explain how landforms affect climate.

National Science Education Standard:
CONTENT STANDARD D: Earth and Space Science
ENERGY IN THE EARTH SYSTEM

• Earth systems have internal and external sources of energy, both of which create heat. The sun is the major external source of energy. Two primary sources of internal energy are the decay of radioactive isotopes and the gravitational energy from the earth’s original formation.

• Heating of earth’s surface and atmosphere by the sun drives convection within the atmosphere and oceans, producing winds and ocean currents.

• Global climate is determined by energy transfer from the sun at and near the earth’s surface. This energy transfer is influenced by dynamic processes such as cloud cover and the earth’s rotation, and static conditions such as the position of mountain ranges and oceans.

GEOCHEMICAL CYCLES

• Movement of matter between reservoirs is driven by the earth’s internal and external sources of energy. These movements are often accompanied by a change in the physical and chemical properties of the matter. Carbon, for example, occurs in carbonate rocks such as limestone, in the atmosphere as carbon dioxide gas, in water as dissolved carbon dioxide, and in all organisms as complex molecules that control the chemistry of life.

Teacher Background
A rain shadow (or more accurately, precipitation shadow) is a dry region on the surface of the Earth that is leeward or behind a mountain with respect to the prevailing wind direction. A rain shadow area is dry because, as moist air masses rise to top a mountain range or large mountain, the air cools and the maximum moisture content decreases until it reaches the dew point, where the water vapor condenses as rain or snow and falls on the windward side or top of the mountain. This process is called orographic precipitation. The effect of the process is the creation, on the leeward side, of an area of descending dry and warming air, and a region that is quite arid.

Related and Resource Websites
Monsoons in Arizona http://www.naturescience.org/Monsoons.html
Nature of Rainfall http://www.personal.psu.edu/users/c/x/cxb382/
The Weather http://www.olypen.com/stelow/aboutarea.html
Prevailing Conditions http://www.hawaii.gov/dbedt/czm/wec/html/weather/prevailing.htm
Water as a Climate Moderator http://www.waterencyclopedia.com/Ce-Cr/Climate-Moderator-Water-as-a.html
AccuWeather.com http://wwwa.accuweather.com/news-blogs.asp?partner=accuweather&blog=abrams
JStor on The Rain Shadow Effect of the Plant Formation of Guadalcanal: http://www.jstor.org/view/00129615/di960609/96p0024x/0
Wikipedia on Rain Shadow http://en.wikipedia.org/wiki/Rain_shadow

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Activity
Part One – Sea Breezes and Land Breezes

1. Ask students how they think water affects the climate. How do they think the sun and water interact to affect climate?

2. Allow a few minutes for students to share responses before beginning the experiment.

3. Divide the class into groups. {How man students per group approximately?)

4. Have each group set up the following:

  1. one cup of dark colored sand,
  2. one cup of light colored sand, and
  3. one cup of water.

5. Have students take the initial temperature of the materials and place the materials equi-distant from a heating lamp. While they are working on the rest for the lab, they should go back to check the temperature every 5 minutes approximately.

6. Once water and land have reached the same temperature, have students remove the heat lamp and allow the materials to cool, noting the temperature every 5 minutes. How long does it take each material to cool? Have students graph their findings.

7. Which one heats faster? [Land] Which holds its’ heat longer? [Water] How might that affect winds? Remember hot air rises. [As the land heats, the hot air rises. Cool air is denser and higher in pressure than warm air, and high pressure moves toward lower pressure. This is an ocean breeze. In the evening the air is cooler over the land and a land breeze is created as the warm air above the ocean rises and the cool, more dense land air rushes in to take the place of the warm evening ocean air.]

Part TWO – Orographic Lifting & Rain Shadows
1. When students enter the room, have the following question written on the board: Consider a state on the West coast of the United States. Would you expect a lot of rain there? Why or why not? Explain.

2. Allow students a few minutes to prepare their answers. When they have finished writing, have them share their responses with the class. [Hopefully you will have some dissent. Some students will say there should be rain since it is near an ocean and the winds come from the West. Others may say you can’t tell since we don’t know the latitude.]

3. Tell students today they will be focusing on the climate of Oregon. (Oregon is an ideal state to study, because it is coastal, has large mountain ranges, and is far enough North not to be affected by the high-pressure zone that plagues states near the boundary between the Hadley and Ferrell Cells.)

4. Divide the class into groups and distribute the map of Oregon and the Average Rainfall Handout.

5. Have students plot the amount of rainfall and devise a color-coded key that explains patterns of rainfall in Oregon, i.e. places that experience 0-50 cm of rain a year are red, 50-100 cm of rain are yellow, etc.

6. What patterns do they notice? [More rain West side of the state than East.] What is that pattern?

7. What might cause the pattern to repeat itself year after year? [The mountain range affects rainfall on either side of the mountain.]

8. Tell students they have been studying rain shadow effect. When warm moist air is blown in and forced up over a mountain range, it cools adiabatically. Ask students what they think adiabatic means? Why might air cool as it rises? As a class, come up with a definition of adiabatic cooling. In fact, it cools so much the water molecules condense and collide until they become too heavy, turning to rain or snow. Rain commonly develops this way, but not always.

9. Ask students to think about other rainy places in the United States that are probably not caused by rain shadow effect. Remind students to think about the prevailing winds as well as the proximity to water. Tell students while proximity to water and mountains are ways a location can get rain, there are others. The next two lessons will recover cold and warm fronts to see their effects on precipitation.

10. Given a fictional coastal city known for its traffic congestion and large industrial base located in front of the mountain range students should suggest potential environmental health issues that may arise as a result of sea breezes and adiabatic cooling. How would this impact be different from the similar sized city to the East of the mountains?

Embedded Assessment
Can students plot rainfall correctly? Do they see patterns in the data? Can students explain how landforms affect climate?

 


PULSE is a project of the Community Outreach and Education Program of the Southwest Environmental Health Sciences Center and is funded by:


an
NIH/NCRR award #16260-01A1
The Community Outreach and Education Program is part of the Southwest Environmental Health Sciences Center: an NIEHS Award

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Supported by NIEHS grant # ES06694


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Last update: November 10, 2009
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