Albedo
Albedo describes the reflectivity of a surface and how much short-wave radiation it absorbs or reflects. Recall that insolation from the Sun enters Earth's atmosphere as relatively short wavelengths of the electromagnetic spectrum: Ultraviolet (UV), visible, and near infrared energy. As you learned in the previous activity, some of the incoming insolation is reflected either back out to space or into the atmosphere without ever being absorbed at the surface. The amount of energy that is reflected is determined by the albedo of the surface.
Albedo is an easy concept to grasp for anyone that skis or snowboards, or has ever had to walk across black asphalt on a sunny summer day. White surfaces have HIGH albedo, meaning that they reflect most of the insolation that strikes the surface. Black surfaces have LOW albedo, meaning that they absorb most of the insolation that strikes the surface. Here are some common surfaces found throughout Idaho at different times of the year. Ask yourself the following questions about each one:
1. Does it have relatively high, low, or moderate albedo?
2. How much incoming insolation does it absorb versus reflect?
3. On a sunny day, would this surface likely feel warmer or cooler to the touch than the air temperature?
4. What happens to the energy absorbed by this surface? It is radiated or emitted back out as longwave thermal radiation? Does it get used by plants for photosynthesis? Does it get absorbed by water in order to produce a phase change (e.g., melting ice or evaporating standing water)?
Albedo is an easy concept to grasp for anyone that skis or snowboards, or has ever had to walk across black asphalt on a sunny summer day. White surfaces have HIGH albedo, meaning that they reflect most of the insolation that strikes the surface. Black surfaces have LOW albedo, meaning that they absorb most of the insolation that strikes the surface. Here are some common surfaces found throughout Idaho at different times of the year. Ask yourself the following questions about each one:
1. Does it have relatively high, low, or moderate albedo?
2. How much incoming insolation does it absorb versus reflect?
3. On a sunny day, would this surface likely feel warmer or cooler to the touch than the air temperature?
4. What happens to the energy absorbed by this surface? It is radiated or emitted back out as longwave thermal radiation? Does it get used by plants for photosynthesis? Does it get absorbed by water in order to produce a phase change (e.g., melting ice or evaporating standing water)?
Freshly fallen snow in the Sawtooth Mountains.
Basalt lava fields at Craters of the Moon National Monument in spring.
Senesced (dead) grass on the Snake River plain in September.
Wheat fields in the early summer.
Healthy pine forest in northern Idaho near Wallace.
Recently burned pine forest in Idaho.
(Think about it: how will the changed albedo affect the surface temperature of this dead forest versus the healthy one above?)
(Think about it: how will the changed albedo affect the surface temperature of this dead forest versus the healthy one above?)
Relatively deep water at Ponderosa Pine State Park near McCall.