| Understanding the natural environment involves studying 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.
Background
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. Below is a brief overview of some of the the many factors that influence the temperature of a surface. For a more thorough explanations, please do an internet search or ask questions on the bulletin board.
Sunlight: Sunlight provides the energy that warms Earth's surface. Anything that reduces sun exposure will lower temperature. That might include shading, reflection, and the angle at which the sun's rays strike the ground.
Albedo: The percentage of sunlight reflected from a surface is called its albedo. The energy in sunlight remaining after reflection is absorbed by the surface. All else being equal, the greater the albedo, the cooler the surface because less sunlight is absorbed. In general, darker surfaces, like asphalt, have low albedos and thus, under the same sun exposure, heat up more than reflective surfaces such as snow, grass, or concrete because they reflect less and absorb more of the available sunlight.
Evaporation: When water is available, evaporation absorbs large amounts of energy and reduces heating. Cooling by evaporation is one of the fundamental ways that plants and animals, including humans, shed excess heat. When no water is available, all sunlight energy absorbed is used in heating the surface and it can become quite hot. Which is hotter: bare sand or nearby grass? Grass roots send soil water to the leaves where it evaporates and cools the plant.
Surface Material Properties: One of the most important properties that affect temperature is a material's specific heat capacity, which is ratio of energy added to temperature increase. Water has the highest specific heat of any common substance in nature, meaning that it takes a lot of energy to heat it up compared other surfaces like concrete, soil, forest or anything else. This explains, in part, why lake and ocean surfaces heat up much more slowly than the nearby land areas during sunny days.
For this lab you need:
1.Time ______________ Date _______________ Sky Conditions __________________ Location ___________________________
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 hottest? ______________________________________________________________
Which do you think would be coolest? ______________________________________________________________
If the area received a light rain, how do you think that would affect the surface temperature? ______________________________________________________________
Use the infrared (IR) thermometer to record the following temperatures. When using the IR thermometer, put the instrument CLOSE to the surface being measured, maybe an inch or couple of centimeters away. You should turn the laser pointer off, it is misleading. DO NOT stand several feet away and just aim the instrument using the laser pointer, you will not get an accurate reading on the small surface area required for this lab. Sometimes the side of the IR thermometer shows the angle of measurement, this helps explain why you need to hold the instrument close to what is being measured. Same with the sky measurements below, try an find as large an area of clear sky or cloud as possible to aim at.
Ambient Air Temperature
Air temperature as reported by meteorological services around the world is recorded in a white, shaded box called a Stevenson screen, with open airflow and a thermometer mounted at two meters above the surface, hence sometimes called 2m-temperature. As we do not have a standard thermometer for measuring air temperature, we will use a proxy that should give a fairly reliable result. Measure the SHADED side of a tree trunk at around head height. The trunk should have been in the shade for an hour or more to ensure that it approximates the ambient air temperature. Deep shade is best. Be sure to put the instrument CLOSE to the tree trunk, like a couple of centimeters or an inch, when taking the measurement, not 2 or 3 meters away.
3. __________ Temperature on shaded side of a tree at head height. Deep shade is best. Blocked from the wind is best. We will assume this is a close approximation of ambient air temperature.
Take the following temperature measurements:
Temperature Profile to determine Heat Flow near the Surface
In nature, heat flows from areas of higher temperature toward areas of lower temperature. We will explore the direction of heat flow near the surface on a sunny day. In an open, sunlit area of bare dry soil, measure the temperature using the IR thermometer at the following places. For the below-ground measurements, use the digging tool to expose the soil at the listed depths and then use the IR thermometer to measure the temperature in the hole. Be sure to place the IR thermometer CLOSE, but not touching, the soil.
Albedo, Surface Characteristics, and Surface Temperature
Now measure the temperature of several different surfaces that have been exposed directly to sunlight for at least several minutes. Do not take these measurements in a shaded area.
7. ________ sunlit side of tree trunk
8. ________ sunlit grassy area
9. ________ shaded grassy area
10. ________ sunlit concrete
11. ________ shaded concrete
12. ________ sunlit asphalt
Effect of Evaporation on Temperature
For this measurement, we will measure the temperature of an open surface exposed to sunlight, then mist it with water, wait until the water evaporates away and then measure the temperature again.
13. ________ concrete in sunlight before wetting
14. ________ concrete after water has evaporated
15. ________ tree trunk in sunlight before wetting
16. ________ tree trunk after water has evaporated
Clouds and Greenhouse Warming
Clouds are an important part element of greenhouse warming. For these measurements point your IR thermometer at blue sky and clouds, but DO NOT POINT DIRECTLY AT THE SUN!!!!! or you will destroy the instrument. Do your best with these measurements, it will not be possible to get clean measurements of all items below, but you should be able to get reasonable enough measurements to show the general relationships.
17. ________ large patch of blue sky overhead
18. ________ base of large area of cumulus clouds as high overhead as possible
19. ________ thin high clouds (if available, just put N/A if no thin clouds)
Other
Feel free to play around the the instrument, there are lots of interesting variations in temperature in the environment. Try measuring your skin at different places. Where is it hotter and cooler?
Answer the following questions based on your measurements and the background information given at the beginning of this lab. Some of the answers will be speculative so do not be afraid to use your imagination, in other words - guess.
Sun and Shade.
20. How many degrees warmer was the sunlight area than the shaded area of the: a) tree trunk ___________, b) grass _______________, and c) concrete ___________?
21. Which surface had the greatest difference in temperature between sunny and shaded areas? _____________ Speculate: Why you think that surface was heated the most by direct sunlight? ____________
22. Speculate: Why you think there was a difference in the amount of warming by sunlight for the different surfaces. What physical characteristics of the surfaces could be responsible for the difference? Use reason and imagination in answering. _______________________
Temperature Profile
23. In nature, heat flows from warmer areas toward colder areas. Based on your measurements in 3 and 4, where is the higher temperature - at the surface (#4) or the air above the surface (#3)? ________________ Based on this result, which direction is heat flowing - from the surface upward into the air, or from the air downward to the surface? _____________ Remember, heat flows from warmer areas toward cooler areas.
24. Based on your answer above, during the day, does the ground heat the air or does the air heat the ground? _____________
25. Based on your measurements in #4, #5, and #6, where is the higher temperature - at the surface or the soil below the surface? ___________ Based on this result, which direction is heat flowing - from the surface downward into the soil, or from the soil upward toward the surface _____________? Remember, heat flows from warmer areas toward cooler areas.
26. Assume that, at night, the bare soil surface temperature falls to 20 oC (68 oF) and the temperatures below the surface that you measured in #5 and #6 remain the same. Under these conditions at night, which direction will heat flow - from the surface downward into the soil, or from the soil upward to the surface? _____________ Explain your answer, why is heat flowing that direction at night?______________
Effect of Evaporation
27. How many degrees did wetting cool the concrete?______________ How many degrees did wetting cool the tree trunk? ______________ What caused the temperature to drop? ____________________ (Do not say "it got wet," state the physical process that caused the cooling)
28. Did concrete or the tree trunk cool more when wet? ___________________ Why do you think there was a difference? ________________
29. Compare your measurements of the sunlit, open grass (#8) and bare, dry soil (#4) areas, which was hotter? _________ Both are exposed to the same amount of sunlight, and grass has a lower albedo than bare soil, so why do you think there was a difference in temperature? _____________________________
Albedo
30. Which surface was hotter, concrete or asphalt? ________________ Which was darker? ____________________
31. Do you think darker or lighter surfaces will be hotter in general? ________________ Why? ____________________
Urban Heat Island
32. Which surface was hotter, grass or asphalt? ________________ Why do you think it was the hottest? ________________
33. Ever hear of an "urban heat island?" The phrase refers to the observation that urban (city) areas are almost always hotter than the surrounding rural (country) areas. Based on your measurements and answers above, give two reasons that urban areas might be hotter than rural areas.
First Reason: ________________________________
Second Reason: ______________________________
Application
34. There was a lot of variation in the surface temperature measurements. Under what conditions would you expect all of your measurements to be approximately the same? ___________
35. Compare your surface temperature measurements to your initial beliefs given in #2 above.
Did the measurements prove you right for the coolest and hottest surfaces? __________
If not, what were the differences? _________________
36. 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 reduce their surface heating due to direct sunlight. (HINT: which measurements had the lowest temperatures?).
Sky
37. Which was warmer, cloud or clear sky? _____________ Clouds can have an important effect Earth's surface temperature. Based on your measurements, do you think the surface would be warmer at night under clouds or clear sky? _______________ Explain your reasoning. ________________
38. Clouds have a major effect on planetary temperatures by influencing the amount of sunlight absorbed and reflected by the planet and through an analog with the so-called greenhouse effect. The greenhouse effect traps heat in a planet's atmosphere. From the surface, the greater the greenhouse effect, the warmer the sky appears. Based on this information and your measurements, do you think that more clouds would increase or decrease the planetary greenhouse effect? ______________________ Explain your reasoning _____________________________.
39. What was the difference in degrees between the air temperature (#3) and the cloud base temperature (#18)? ________________ Under dry conditions, rising air cools at about about 10 oC per kilometer (5.5 oF per 1000 ft). Based on this information, how high would the surface air have to rise to match the cloud base temperature that you measured? _____________________ (HINT: subtract cloud temperature from surface air temperature (#3) and divide by either 10 oC or 5.5 oF, depending on the units you are using.)
40. Please tell me about how long it took you to complete this lab and what significant problems you had. Thanks.