Part 3—Zoom In for a Closer Look
Step 1 – Reduce the Time Frame of the Graph from Two Years to One
Most of the graphs in Part 2 showed data across a two-year time frame. This was helpful for looking at patterns that repeat on an annual cycle. In this part of the challenge you will use various date features to zoom in for a more detailed look at the data sets and the relationships that exist among them.
- Return to the GLOBE graphing tool. In the dialog box, click the Select Date button. In the drop-down list that opens, scroll down to 1999 and select it. Then click Redraw.
- Click the Select Date button.
- In the drop-down list that opens, scroll down to 1999 and click on it.
- Click Redraw.
- Some patterns should now be easier to see, and you'll be able to get a better sense of what the year was like. Examine the image while considering the following questions:
- At approximately what date in 1999 did the maximum air temperature start to regularly reach above 12 degrees C?
- At approximately what date in 1999 did the maximum air temperature start to frequently rise above 30 degrees C?
- At approximately what date did the soil moisture at 10 cm first drop below .22 g/g?
- At approximately what date did the soil moisture at 90 cm first drop below .22 g/g?
Responses may vary. Some might claim that maximum air temperature is regularly above 12 C by the start of April; others may claim late April.
The maximum air temperature start to frequently rise above 30 degrees C in late June.
The soil moisture at 10 cm first drop below .22 g/g in late April, but not until late June for the 90 cm depth.
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Step 2 – Change the Time Frame to Limit the Graph to January, February, and March, 1999
- In the lower date control line, which establishes the end of the time frame, change the ending date of the time frame to March, by changing Month=12 to Month=03. Be sure the four data sets are still highlighted, the graph size selection is large, and the Data (Y) Axis Range is Use a fixed range. Click Redraw.
- Download, rename, and save the image. Now re-open the image and print it.
- In the lower date control line, which establishes the end of the time frame, change the ending date of the time frame to March, by changing Month=12 to Month=03.
- Be sure the four data sets are still highlighted, the graph size selection is large, and the Data (Y) Axis Range is Use a fixed range.
- Click Redraw.
- Examine the image while considering the following questions.
- On approximately how many days does the maximum air temperature get above freezing?
- During this three-month period, how much change do you notice in the soil moisture content at a depth of 10 cm below the surface? At 90 cm below the surface?
The maximum air temperature get above freezing approximately 55 days out of 90 days. There is very little change in the soil moisture content.
Step 3 – Change the Time Frame to Limit the Graph to April, May, and June, 1999
- In the upper date control line, which establishes the start of the time frame, change the Month=01 to Month=04. In the lower date control line, that establishes the end of the time frame, change the Month=03 to Month=06, and change the Day=31 to Day=30.
- Download, rename, and save the image. Now re-open the image and print it.
- Examine the image while considering the following questions.
- Between the end of April and approximately May 19, describe what happens to soil moisture content at 10 cm. Look at the rainfall pattern between April 25 and May 19. Does this help explain the change in soil moisture at 10 cm?
- On approximately May 19 and again on May 22 there is a sharp rise in soil moisture content at 10 cm. Why do you think this happened?
- What happens to the soil moisture content at 90 cm during the second half of June? How do you explain this change?
- In addition to the data in the graph, can you think of any other natural changes that happen in the northern US during this time that might help explain the decrease in soil moisture content?
Soil moisture a depth of 10 cm drops steadily between the end of April and May 19. There was very little rain during this time, and the soil moisture was probably not frozen since the maximum air temperatures were well above freezing throughout the period. The soil moisture may have moved into vegetation that was growing at that time. This happened because rain at those times increased the soil moisture level.
There is a slight increase in soil moisture at 90 cm depth following the rain event of mid June, and then the level drops moderately. There is no precipitation during this period and temperatures are increasing, so more water is evaporating from the soil and less is penetrating to the 90 cm depth.
In the spring plants that have been dormant for the winter start growing again, in response to increased temperatures sunlight. The roots of trees, shrubs, and smaller plants will draw water out of the soil, hold some, and transpire moisture into the atmosphere.
Step 4 – Change the Time Frame to Limit the Graph to July, August, and September, 1999
- In the upper date control line, change the Month=04 to Month=07. In the lower date control line, change the Month=06 to Month=09.
- Be sure the four data sets are still highlighted, the graph size selection is large, and the Data (Y) Axis Range is Use a fixed range. Click Redraw.
- Download, rename, and save the image. Now re-open the image and print it.
- Examine the image while considering the following questions.
- What patterns or trends do you see in the Maximum Temperature across these three months? How do they compare with the maximum temperature patterns or trends where you live?
- For a period of almost two weeks in July, no soil moisture data was collected. What assumption would you make about the soil moisture at 10 cm during that period of time, and what would be the basis of that assumption?
- During late July (and possibly for most of July), soil moisture at 10 cm is quite steady, when compared to the changes that occur throughout much of August. How would you explain this?
Maximum air temperatures tend to rise slightly during July and drop slightly across August and September. [Responses to the second question will vary; encourage students to research the average daily temperatures for their own location.]
A reasonable assumption is that the soil moisture at a depth of 10 cm rose after the rain event on July 5, then dropped because of the long period without rain when vegetation was removing moisture from the soil, then rose again with the rain event of July 18 and 19.
The rain events in August were more frequent and more significant than they were in July. This would cause more frequent change in soil moisture at a depth of 10 cm.
Step 5 – Change the Time Frame to Limit the Graph to October, November, and December, 1999
- Change the time frame dates so that they will create a new graph that shows just the last three months of 1999.
- Be sure the four data sets are still highlighted, the graph size selection is large, and the Data (Y) Axis Range is Use a fixed range. Click Redraw.
- Download, rename, and save the image. Now re-open the image and print it.
- Examine the image above while considering the following question.
- Compare the graph for the last three months of 1999 with the graph for the first three months of 1999. In what ways are they similar? In what ways do they differ?
Similarities: In both the first and last three months of the year, temperatures are cooler and rain events seem to have less of an influence on soil moisture at 10 cm that during the six warmer months.
Differences: During much of the first three months, the ground is most likely frozen (judging from the maximum air temperatures) and soil moisture levels barely change. During most of the last three months of the year the ground is not frozen and soil moisture levels change, although not very dramatically. It's possible that dead leaves and other vegetation on the ground absorb and evaporate some of the rain.
Step 6 – Connect the Three-Month Graphs to Construct a Large Full-Year Graph
Trim the print-outs of the graphs so that they don't overlap, and tape them together to create a single, long graph that shows all of 1999. Then, compare this 4-sheet graph with the graph that shows all of 1999 on a single sheet.
Examine the image while considering the following questions.
- Do the two graphs give you different impressions? Is having both better than having just one or the other?
- Use one or both graphs to help you write a summary of how Maximum Air Temperature, Soil Moisture at 10 and 90 cm, and Rainfall vary across the year in Greenville, PA, and how they influence one another.
Responses will vary. The general seasonal patterns of maximum air temperature and soil moisture seem to stand out more clearly when the data for a whole year is compressed in a single smaller graph. The specific influence of precipitation events and other details seem easier to see on the larger graph. Having both representations seems better than having just one or the other.
Responses will vary but here are some key ideas. In Greenville, rainfall is recorded in all twelve months of the year, but during the winter when the ground is frozen and the vegetation is dormant, soil moisture at depths of both 10 cm and 90 cm are unaffected and thus remain constant. When maximum air temperatures remain above freezing during spring, summer, and fall, rain can penetrate the soil to increase soil moisture levels (particularly at the 10 cm depth) and vegetation becomes active to decrease soil moisture levels. For these months, soil moisture at a depth of 10 cm increases and decreases frequently to reflect the influence of these two factors. Soil moisture at 90 cm responds less to rain events and more to the growing season, when it tends to drop as vegetation becomes active. There are times when a significant rain event will cause a short-term jump in soil moisture at 90 cm, but that is uncommon. Once vegetation becomes inactive in the fall, and before the ground freezes, rain events cause the soil moisture at 90 cm to rise.
Once data is available in graphic form, aspects of Earth's complex system can start to become more obvious; patterns and relationships that may be difficult to notice without the graphs will start to emerge. For example, one might have guessed that soil moisture was greater in months when more rain occurred, which are the warmer months for Greenville, PA. Having the data makes it clear that soil moisture is actually greater in the cold months.
In Greenville, the natural vegetation is less active or dormant in the winter. Deciduous trees lose their leaves. The ground freezes and can become covered with snow or ice. There is less solar energy. In the warmer months, there are three natural changes that can reduce soil moisture. Increased solar energy thaws the soil and at some point causes evaporation. Trees and other vegetation become active, draw water out of the soil, and release it into the air. This is called transpiration. Finally, wind can increase both evaporation and transpiration.
