Earth's Heat Budget and the Greenhouse Effect
- Extend knowledge of several aspects of the earth's global average surface,
atmospheric, and whole-earth heat budgets to consider spatial variability.
- Investigate connections between spatial variations in the heat budget
and properties of the earth, such as albedo, vegetative cover, rainfall distribution,
distribution of water vapor, and topography.
Introduction. In Lab
Activity #5, "Long-Term Average Heat Budgets for the Earth's Atmosphere
and Surface" we examined the global, long-term average heat budgets
for the earth's surface and atmosphere, accounting for radiative energy as
as other forms of energy. The numbers come from Meteorology, 1998, an
introductory textbook by Danielson et al., and are similar to those found in
many texts (though in 2009 the numbers were updated using more recent observations and better methods). In this lab you will investigate how these 1998 numbers compare
to the observations in the My World GIS data sets; investigate spatial variability
in several aspects of these budgets; and investigate possible connections between
some of these variations and properties of the earth.
Getting Started. Using one of the computers in TH 604, TH 607, or TH 518, run My World GIS and load the project called "Lab06_Albedo_GHEffect.m3vz", located in the same place as our previous My World GIS projects, in student [Home] > Courses > E535 > Classes.
Part 1: Albedo
(1) Annual-average albedo plot. Make sure that the "MonAvg_Radiative BudgetTerms.wwf" panel is highlighted (by clicking on it). In that panel, pull down the field menu and select "Annual Average Planetary Albedo 1987". (This field was calculated by dividing the annual average reflected solar for by the annual average incoming solar for each latitude/longitude cell. This is probably not the best way to calculate the annual average albedo, but limitations of My World GIS forced this less satisfactory alternative.)
Suspicious albedoes. Do you see any values greater than 1.0 or undefined values? Should
there be any such values, and if there are, what might account for them?
- Global, annual-average albedo. Look up the area-weighted global mean annual-average albedo (in the row of icons across the top of the Layer List", click on the summation symbol—the capital Greek letter sigma) and compare it to the value given in the
global heat budget diagrams provided in class with Lab
Activity #5. Are they very
different? (If so, what might account for the difference?)
- Spatial patterns of albedo. On the (unweighted) annual-average albedo plot, where does albedo tend to be relatively low and relatively high,
compared to immediately surrounding areas? (Focus on larger scale areas and deemphasize small, individual spots.) Pose some hypotheses about
what might account for some of these variations.
Comparison with spatial patterns of precipitation. Open a child window containing the annual-average albedo (pull down the "Windows" menu along the top of the main My World GIS window and select "New Child Window ..."), then hide the radiation budget terms layer (by clicking on the "eye" symbol in the upper right-hand corner of the MonAvg_RadiativeBudgetTerms.wwf" panel). Now, open the "MonAvg_Precipitation.wwf" panel (by clicking on the blank box in its upper right-had corner, so an "eye" symbols appears in the box). You should see "Annual Average Precipitation 1987" plotted (though if not, pull down the field menu in the panel and select that field). Does this plot help you test any of
your hypotheses in (1)(c)? If so, how?
Annual-average clear-sky albedo plot. If your child window is still open, close it. Close the MonAvg_Precipitation.wwf panel and re-open the MonAvg_RadiativeBudgetTerms.wwf panel. Pull down its field menu and select the "Annual Average Clear Sky (No Clouds) Planetary Albedo 1987" field. This shows the annual-average
reflected solar radiation from the earth under "clear sky" conditions
(that is, with clouds removed).
Spatial patterns of clear-sky albedo. Where does the clear-sky albedo tend to be relatively low and relatively high?
Does this plot help you test any of your hypotheses about the reasons
for spatial variations in albedo in (1)(c) above, and if so, how?
- Comparison with spatial patterns of vegetation. Open a new child window with the clear-sky albedo plot in it, then close the MonAvg_RadiativeBudgetTerms.wwf panel. Open the "Terrestrial Biomes" panel. You should see the the "Dominant Vegetation" field plotted (but if not, pull down this panel's field menu and select that field). Comparing this plot with the clear-sky albedo plot in the child window, would you say that
hypotheses in (1)(c)? If so, how?
(3) Animations of monthly-average albedo plots. In a Web browser, access a 12-month animation (movie) of individual, monthly-average albedo plots from the ERTH 535 class backup Web site at: http://funnel.sfsu.edu/courses/erth535/S18/MyWorldPlots/Albedo_1987/Albedo_1987.gif.
Open a separate
window in the browser (pull down the "File" menu and select "New..." or "New Window") and access a second movie, a 12-month animation of individual, monthly-average clear-sky albedo plots at: http://funnel.sfsu.edu/courses/erth535/S18/MyWorldPlots/Albedo_1987/AlbedoClear_1987.gif.
- What temporal patterns (that is, patterns of variation over time) do you see in each animation? Pose
hypotheses about what might cause them. Do the two animations together
help you test any of your hypotheses? If so, how?
- Do any of these patterns help you test any of your hypotheses in (1)(a)?
If so, how?
Part 2: Greenhouse Effect
(4) Comparisons among heat budget calculations. In Lab Activity
#4: "Introduction to the Earth's Heat Budget", you used monthly-average
surface temperature data and the Stefan-Boltzmann Law to estimate the global,
annual-average flux of longwave IR emitted by the earth's surface. You also examined a plot of area-weighted, annual-average outgoing longwave IR from the top of Earth's
atmosphere and got a global average from it. You have looked up the area-weighted, global,
annual-average flux of incoming solar radiation.
How do these three values compare with the ones in the heat budget figures
provided in Lab Activity
#5: "Long-Term Average Heat Budgets for the Earth's Atmosphere and Surface"?
[Note: to make this comparison, you'll have take into account the fact that the heat budget numbers that appear in the figures provided in class are not fluxes but rather percentages of
the incoming solar radiation flux. Hence, you'll have to apply those percentages to the long-term, global average insolation to get the heat budget figures as fluxes instead of percentages.] If the two sets of figures seem
significantly different, can you think of any reasons to explain those differences?
(5) Annual-average greenhouse effect and greenhouse increase.
- Close any open child windows and the Terrestrial Biomes panel. Open the "MonAvg_GreenhouseEffect.wwf" panel and click on the panel to highlight it.
- Access the documentation about the greenhouse effect data set (pull down the "Layer" menu along My World's topmost menu bar, and select "Show Data Documentation"). How is "greenhouse effect" defined for these data?
- Look up the area-weighted global average greenhouse effect.
the foregoing steps for the "MonAvg_GreenhouseIncrease.wwf" panel.
- Comparison of global-average greenhouse effect calculations. Is the area-weighted, global-average greenhouse increase consistent with the global-average
surface temperature and the effective radiative temperature for the earth
(as viewed from space) that we got in Lab
Activity #4: "Introduction to the Earth's Heat Budget"?
- Spatial patterns in the greenhouse effect. What spatial/geographic patterns do you see in the annual-average greenhouse
effect? Pose hypotheses to try to account for
some of them.
- Possible correlations between the greenhouse effect and other quantities. Open your choice of any one or more of the following panels:
- Elevation & Bathymetry (pay attention to land only). (You should see a plot of terrain elevations "normalized" by the average elevation of land areas in the data set—that is, divided by the mean elevation above sea level of land, which is 677 meters in My World's data set.)
- MonAvg_Precipitable_H2O_Vapor.wwf. (Find out what "precipitable water" is by consulting the documentation about this panel. You should see a plot of annual-average precipitable water for 1987 normalized by its unweighted global average value.)
- MonAvg_SpecificHumidity.wwf. (Follow the same procedure as for precipitable
- MonAvg_SurfaceTemperature.wwf. (You should see a plot of annual average surface temperature for 1987.)
Create a child window for your plot. Close the panel for your current plot, then open the MonAvg_GreenhouseEffect.wwf panel, pull down its field menu, and select "Annual Avg GH Effect Normalized by Global Avg 1987".
Do any of these four quantities seem to be relatively well correlated spatially with
the greenhouse effect? (The term "correlated" can be defined
in a mathematically rigorous way, but here all we want is a subjective
of whether or not the plot patterns resemble each other closely.) Of these
four, can you think of some that might be well correlated with each other?
What physical connections do you think there might be between each pair
of well-correlated plots that would make the correlations more than accidental?
Home |*| ANNOUNCEMENTS |*| Syllabus |*| Assignments, Handouts, etc.