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Radiation and Climate Thermal Properties at Earth’s Surface 1.

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Presentation on theme: "Radiation and Climate Thermal Properties at Earth’s Surface 1."— Presentation transcript:

1 Radiation and Climate Thermal Properties at Earth’s Surface 1

2 Colors If you have visited the South or Southwest, you may have noticed that many cars are light colored, both inside and out. Do you know why? If you had to walk barefoot across an asphalt parking lot on a hot, sunny day, you would probably find that carefully walking on the white, painted stripes is more comfortable than walking on the dark asphalt. Why? 2

3 Reflectivity When solar radiation strikes a surface, some photons are absorbed, which increases the surface temperature, and other photons are reflected. – The proportion of radiation that is reflected, expressed as the material’s reflectivity, does not raise the object’s temperature. – Light-colored surfaces reflect more radiation, and therefore remain cooler, than dark-colored surfaces. For example, clean snow reflects almost 95% of solar radiation, whereas forests reflect very little – Variations in the reflectivity of materials at Earth’s surface help determine local surface temperatures. 3

4 Asphalt absorbs almost all solar radiation that strikes it, which causes asphalt roads to become quite hot and radiate heat. n-Australia/Perth/blog html 4

5 Clean snow has reflectivity, but trees by contrast, possess relatively low reflectivity— when they’re not snow-covered as depicted here. /skier_1.html 5

6 Specific Heat Capacity Every material has a characteristic reflectivity and heat capacity, which together determine how much and how fast the material warms. Specific heat capacity is the quantity of thermal energy (heat) needed to raise the temperature of one gram of a substance by one degree Celsius. 6

7 “Storage Capacity” In effect, a specific heat capacity value for a material can be considered as its “storage capacity” for thermal energy. – The lower a material’s specific heat capacity, the higher its temperature will rise if a certain quantity of thermal energy is added. – The higher the specific heat capacity of the material, the less its temperature will rise for a given quantity of added thermal energy. 7

8 Examples Materials with higher specific heat capacities can store more thermal energy. – For instance, copper metal, with a specific heat capacity of J/g°C will have a larger temperature change in response to the same quantity of thermal energy added than will water, with a specific heat capacity of 4.18 J/g°C. – In particular, 10.0 J of thermal energy will raise the temperature of 1.00 g of copper by 25.8°C; however, it will increase the temperature of an equal mass of water by only 2.4°C, which is less than 10% of copper’s temperature increase. 8

9 Specific Heat Capacities for Common Materials at 20°C MaterialSpecific Heat Capacity, J/g°C Air1.00 Aluminum0.895 Asphalt0.92 Brass0.380 Carbon dioxide0.832 Copper0.387 Ethyl alcohol2.45 Gold0.129 Granite0.803 Iron0.448 Lead0.128 Sand0.29 Silver0.233 Stainless steel0.51 Water (liquid)4.18 Zinc

10 Water Water’s unique properties make it influential in the world’s climates. Water’s specific heat capacity is higher than that of most other common materials. Because of this, bodies of liquid water can store large quantities of thermal energy and are thus slow to heat up or cool down. By contrast, land surfaces have much lower specific heat capacities; they heat up and cool down much more readily. 10

11 HOMEWORK 1)a) Compare lake water and asphalt in terms of how readily each warms up when exposed to sunlight. b) What properties of these two materials account for differences in their behavior? 2) From a scientific viewpoint, why do many desert dwellers elect to wear white or light-colored garments? 3) Given their respective functions, compare the specific heat capacities of the material from which the handle of a frying pan is made and the material from which the frying pan itself is made. 11

12 HOMEWORK 4) Given the same energy input, which would you expect to have the greater temperature increase, equal masses of aluminum or iron? Use the table in this PowerPoint to explain your answer in terms of the concept of specific heat capacity. 5) Lake Erie has a water volume of about 484 km 3. How much energy would be required to raise its temperature 1°C? Show your calculations. 12

13 HOMEWORK 6) Normal human body temperature is about 37°C. Room temperature is usually about 25°C: a) How much energy is required to raise the temperature of 1.0 L of aire (density = g/mL) from room temperature to body temperature? b) How much energy is required to raise the temperature of 1.0 L of liquid water (density = 1.0 g/mL) from room temperature to body temperature? c) Using your answers to a) and b), explain why cold water, or even room temperature water, feels colder on the skin than does air at the same temperature. 13


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