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Initial Publication Date: December 2, 2013
Unit 4: Slow and Steady Study Guide
This study guide provides an opportunity to test your understanding of some of the concepts you have learned, as well as new vocabulary. For each of the questions below, provide yourself with an opportunity to try to answer the question before uncovering the clues or the answer.
New Vocabulary or Terminology
- Describe what albedo means.
The reflectivity of a surface. A surface with a high albedo is more reflective than a surface with a low albedo.
- What is a reflectivity anomaly?
An anomaly is a change from normal, so a surface's reflectivity anomaly refers to a change in the surface's reflectivity from its long-term average reflectivity.
- What is MODIS?
MODIS stands for "Moderate Resolution Imaging Spectroradiometer" and is an instrument mounted on some satellites that are orbiting Earth. MODIS instruments obtain data on Earth's entire surface every 1 to 2 days. A variety of data are acquired by MODIS; in exercise 4.2, you used MODIS data to study changes in the areas of several marine-terminating outlet glaciers in Greenland.
- Describe what a marine-terminating outlet glacier is and where they are found.
Outlet glaciers are sometimes referred to as ice streams. They are channelized glaciers that extend from a major ice sheet (like the Greenland ice sheet) and flow more rapidly than the surrounding ice. Greenland's outlet glaciers, terminate and calve into the ocean.
- What is calving?
Calving occurs when sections of ice break off the edge of a glacier.
Conceptual Questions
- During which season is albedo typically lowest on the Greenland ice sheet?
Albedo data indicated that the Greenland ice sheet exhibits the lowest albedo during the summer.
- How is a reflectivity anomaly calculated?
To calculate a reflectivity anomaly, the long-term average reflectivity is subtracted from the current reflectivity. In other words: reflectivity anomaly = current reflectivity - long-term average reflectivity
- What does an albedo of 0.75 mean?
Multiply the unitless albedo value by 100 to obtain a percentage; in this case, 0.75 x 100 = 75%. This means that the surface reflects 75% of incoming solar radiation.
- What are some factors that contribute to albedo differences in Greenland? How do each of these factors influence albedo (i.e., higher albedo, lower albedo)?
- Different materials have different albedos. Most of Greenland is covered with snow and glacial ice, which have higher albedos than rock and vegetation.
- Higher-elevation areas exhibit higher albedos than lower elevation areas because snow and ice exist more readily at higher elevations.
- Albedo varies seasonally, namely, albedo is higher during the colder, winter months than during the warmer, summer months.
- Snow has a higher albedo than glacial ice because of the shape of snowflakes vs. the shape of compressed glacial ice.
- Impurities (pollen, volcanic ash, etc.) may accumulate on top of a glacier, lowering its albedo.
![[creative commons]](/images/creativecommons_16.png)
Provenance: Created by Jason Box, Byrd Polar Research Center. Downloaded with permission from his blog, at http://www.meltfactor.org/blog/?p=514
Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.
Provenance: Created by Jason Box, Byrd Polar Research Center. Downloaded with permission from his blog, at http://www.meltfactor.org/blog/?p=514
Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.
5. Consider the albedo plots on the right, and come up with at least one similarity and one difference between the data (other than the title!).
- Similar: Both plots illustrate similar seasonal albedo trends; albedo begins to drop in the spring, is at its minimum during the summer, and increases again into the fall. It appears that for both plots, June albedo was lowest for 2012.
- Different: The higher elevation plot (right: 2000–2500 m; albedo range from 72 to 92%) illustrates an overall higher albedo than the lower elevation plot (left: 1000–1500 m; albedo range from 50 to 85%). The higher elevation plot exhibits a more dramatic drop in albedo in June than the lower elevation plot.
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