Sunlight and Temperature

Transcription

1 Sunlight and Temperature Name In a previous lab, you studied interactions between the atmosphere, hydrosphere, lithosphere, and biosphere. Many of these interactions involve energy exchanges ultimately derived from sunlight. Sunlight energy pours onto the Earth and shifts from system to system before ultimately departing Earth back to space Purpose: Study microclimate differences due to sunlight exposure, location, and surface; practice environmental measurements; study natural energy flows; compare measurements; and make inferences from findings. When sunlight enters the Earth system, most of it passes through the atmosphere and reaches the surface. Some is then reflected back to space and the remainder is absorbed, heating the ground. This heating is uneven, however, and can vary a great deal over a small area. These variations help produce distinct microclimates, that is places with different temperature, humidity, and sunlight within a small area. In this lab, we will study local variations in surface heating from sunlight. Equipment (provided): thermometer, hole digging tool, water container Ideally, we also would like a hot, sunny day and an area with dry grass, trees, asphalt, bare dry soil, and concrete or rock surfaces nearby. Part 1: Observation 1.Time Date Sky Conditions 2. Survey your area visually. Imagine walking around the area in bare feet. Which surfaces would you prefer to walk on? Which do you think would be coolest? Which would you avoid because you imagine they would be too hot? If the area received a light rain, how do you think that would affect the surface temperature?

2 Part 2: Measurement At several locations, you will measure the surface temperature and also measure one temperature profile. Unless otherwise noted, ALWAYS SHADE THE THERMOMETER BULB. Ever see a Weather Bureau temperature station? It's a white box about head high, with slats to let the air flow and a roof to shield the thermometer from sunlight. Use these directions: For surface measurements, make sure the bulb is shaded and in as much contact as possible with the surface. For air measurements, simply hold the thermometer at the required height and shade the bulb. For soil measurement, push your digging tool into the soil about 3 inches (7 cm) making a hole large enough to insert the thermometer. Insert thermometer making sure it is on contact with soil near the bottom of the hole. For direct sunlight measurements, simply hold the thermometer at the required height without shading. Some of the temperature differences will be small, so please measure carefully and allow the thermometer time to adjust to the new temperature, perhaps a minute or two. Take the following temperature measurements: Temperature profile: In an open (exposed to sunlight) area of bare soil take the temperature (shade the bulb!) 3. head height (shaded, in air) 4. about 3 inches (7 cm) above the surface (in air) 5. touching the surface (the bulb must be in contact with the surface) 6. about 3 inches(7 cm) below the surface (in soil) Surface temperature: Now measure the temperature of several different surfaces. Make certain the bulb of the thermometer is in contact with the surface, that the thermometer is shaded, and allow a couple of minutes to adjust. 7. bare, dry soil (exposed to sunlight, same as number 5 above) 8. wet soil area (soak the same area with water, wait a minute, then record the surface temperature) 9. open grassy area (exposed to sunlight) 10. shaded grassy, area (make sure the area has been shaded for 1/2 hour or more) 11. concrete (exposed to sunlight) 12. asphalt (exposed to sunlight) 13. any other surface of your choosing (exposed to sunlight) Thermometer Exposed to Sunlight 14. sunlit bulb (simply hold the thermometer toward the sun so the bulb is exposed (not shaded))

3 Part 3: Discussion Answer the following questions. Some of the answers will be speculative so do not be afraid to use your imagination. 15. Generalize about the temperature profile (numbers 3-6). Which measurement was hottest? What is the relationship between height above ground and air temperature? How did soil temperature (3" below the surface) compare with surface and air temperature? Why do you think there is a difference? 16. In nature, things (like heat) tend to flow from areas of high concentration to areas of low concentration. Based on your answer regarding the temperature profile above, is heat flowing from the ground downward into the soil, or from the soil upward toward the surface? Why do you think so? Is heat flowing from the surface upward into the air, or from the air downward toward the surface? Why do you think so? 17. What effect did wetting the surface have on your measurements? Try to explain why (guessing is OK).

4 18. How did the measurements in the open grassy area compare with the measurements in the shaded grassy area? Why do you think there was a difference? Under what conditions would you expect no difference in the two measurements? 19. Which surface was hotter, concrete or asphalt? Which was darker? Do you think darker or lighter surfaces will be hotter in general? Why? If you do not know, guess. 20. Which surface was hotter, grass or asphalt? Why do you think it was the hottest? Ever hear of an "urban heat island?" Give one reason that urban areas might be hotter than rural (country) areas.

5 21. What was the temperature of the thermometer exposed to sunlight (#14)? Was this measurement higher or lower than the shaded bulb at head height (#3)? Why do you think there is a difference? 22. Many plants and animals cannot tolerate uncontrolled temperature fluctuations caused by direct sunlight exposure. Based on the various measurements you took in this exercise, suggest at least three (3) ways that plants and animals might keep try to reduce their surface heating due to direct sunlight. (HINT: which measurements had the lowest temperatures?) How did your surface temperature measurements differ from your initial beliefs given in # 2 above? 24. How do you think your measurements would differ on a cloudy day?