METR 104: Our Dynamic Weather (Lecture w/Lab) Lab Exploration #2: Solar Radiation & Temperature Part II: Exploring & Interpreting Data Dr. Dave Dempsey Dept. of Geosciences SFSU, Fall 2012

(10 points)
(Lab Section 1: Wed., Sept. 26; Lab Section 2: Friday, Sept. 28)

Prior Knowledge Required. Before starting this lab activity, you should know the meaning of the words listed below:
• angle (a measure of the degree of "spread" between two intersecting lines)
• down (the direction in which gravity pulls, toward the center of the earth)
• horizon (the points far away where sky meets earth in the absence of obstructions)
• horizontal (oriented in a direction perpendicular to down)
• insolation (intensity of solar radiation striking a surface)
• midlatitudes (latitudes between 30° and 60°, in both hemispheres)
• perpendicular (at an angle of 90° to, at right angles to)
• radiative intensity or flux (rate at which radiative energy strikes a unit of surface area)
• sun angle (angle between the sun and a horizontal surface)
In addition, you should know these facts:
• The approximate diameter of the earth.
• During the earth's orbit around the sun, the approximate time of year when the earth is closest to the sun and when it is farthest from the sun.
• The maximum, minimum, and average distance between the earth and the sun.
• The average insolation on a surface directly facing the sun at the top of the atmosphere.
• The depth of the atmosphere (at least, 99.9% of it).
And finally, you should be able to:
• Identify three reasons why the intensity of solar radiation (insolation) striking a horizontal surface at the top of the atmosphere might vary over time.
• Describe the relation between sun angle and insolation on a horizontal surface that results in a "spreading out" effect.
• Describe the relation between distance from the sun and insolation (at a given sun angle), another kind of "spreading out" effect.
• Describe the relation between sun angle and the distance that solar radiation travels through the atmosphere before reaching the earth's surface.
• Summarize three things that can happen to solar radiation when it enters the atmosphere.
• Describe the combined relation between sun angle and insolation on a horizontal surface at the earth's surface, due to the two factors that contribute to it.
Learning Objectives. After completing this activity, you should be able to:
• Identify ways in which insolation on a horizontal surface at the earth's surface does, or does not, seem to "explain" observed features of daily temperature cycles.
• Describe differences in observed solar radiation intensity:
• over the course of a day
• at the top of the atmosphere on a surface facing the sun vs. on a horizontal surface
• at the top of the atmosphere vs. at the earth's surface, in both cases on a horizontal surface
• at the earth's surface on a horizontal surface at different times of the year
• Propose possible explanation(s) for the differences listed above, and test those explanations using relevant evidence and reasoning
• Identify aspects of this investigation of solar radiation and temperature observations that illustrate aspects of the process of science.
Materials Needed. To complete this activity, you will need:

I. Introduction. Forecasting temperature is one of the most common and useful aspects of weather forecasting. There are various strategies that people use to forecast temperature over the next several days, but modern professional weather forecasters do it by applying their understanding of the underlying physical causes of temperature change to current and recent observations of weather conditions, in a largely quantitative way. In this lab, we will begin to explore some of the physical processes that cause temperature to change.

Almost everyone agrees that temperature varies over the course of a day at least partly because solar radiation varies. To begin investigating this idea, in Lab #2, Part II we will describe and try to explain features of solar radiation intensity observed at one location, and look for connections between observed patterns of temperature and solar radiation over the course of a day.

II. Instructions.
1. Form teams that will conduct the investigations, in collaboration with other teams.

1. The instructor will assign you to a team of several (generally three) people responsible for sharing the work of the investigation. Introduce yourselves.

2. Each team member will be responsible for conducting a different part of the investigation (Section II.C. below) and for explaining the results to the other team members so that they can also explain them.

2. Divide the three tasks listed below among yourselves. Your team must do all three.

1. General Tasks (see details for each task in Section C below):

1. Compare observations of insolation a horizontal surface at the earth's surface in late May and mid December, at the same (midlatitude) location. Also compare each of them to the corresponding temperature observations at the same location over a full 24 hours.

2. Compare observations of solar radiation intensity at the top of the atmosphere (i) on a surface perpendicular to the sun's rays (that is, directly facing the sun) and (ii) on a horizontal surface.

3. Compare observations of insolation on a horizontal surface (i) at the top of the atmosphere and (ii) at the earth's surface, on the same day and at the same (midlatitude) location.

2. Identify the meteograms and/or insolation graphs that seem most relevant to each task. (Group members should all agree.)

3. Form new, temporary "task-focused" teams, and collaborate to carry out and reach consensus about your task.

1. Your instructor will assign each person on your original team to another, temporary team consisting of several people from other teams working on the same task as you are. Introduce yourselves.

2. Address the points listed below that apply to your particular task.

Task B.1.a. (as defined in the Section B.1.a. above):

1. You have been given two meteograms for Hanford, CA, each spanning part of one day and all of the next. One starts on December 15 and runs through December 16, 1998 (local time). The other starts on May 22 and runs through May 23, 1999. On the meteograms the time is labeled in UTC (that is, the standard time in Greenwich, England), not local standard time.

On each meteogram, identify and label some key local standard times, such as midnight, noon, sunrise and sunset. [On December 16, 1998, the sun rose at Hanford at 7:03 am and set at 4:45 pm. On May 22, 1999, the sun rose at 4:44 am and set at 7:04 pm. (On the Web, a source of this information is Naval Oceanography Portal's Sun or Moon Rise/Set Table for One Year, at http://www.usno.navy.mil/USNO/astronomical-applications/data-services/rs-one-year-us.)]

For each meteogram, as best you can, describe the pattern of temperature over the course of a 24-hour day on December 16, 1998 and on May 22, 1999 (local time). (For example, when (Pacific Standard Time [PST]) is the temperature at a minimum, when does it reach a maximum, how does it behave between maximum and minimum points, what are the maximum and minimum temperatures, etc.)

2. You also have two plots of insolation on a horizontal surface at the earth's surface recorded at Hanford, CA, for December 16, 1998 and for May 22, 1999. For each plot, describe the pattern of insolation over the 24-hour day.

3. Identify ways (if any) in which the pattern of insolation observations appears to "explain" the pattern of temperature observations, and ways (if any) that it doesn't, at least not very satisfactorily. (Comment on what you mean by "explain" in this case.)

4. Compare the insolation at the earth's surface for the two time periods, noting similarities and differences between them. Pose two possible explanations for the difference(s) (if any). For each possible explanation, cite a piece of evidence that either supports or contradicts the explanation. (For your explanations and tests, try to use facts and/or ideas from the "Prior Knowledge Required" section of this lab, above, or data from Lab #2, Part I.)

Task B.1.b.
(as defined in the Section B.1.b. above):

1. You have been provided with two graphs showing plots of observed solar radiation intensity (a) on a surface perpendicular to the sun's rays and (b) on a horizontal surface, both at the top of the atmosphere above Hanford, CA. One graph shows these solar radiation intensity observations for the period from (roughly) midnight to midnight on December 16, 1998, while the other shows the same things from (roughly) midnight to midnight on May 22, 1999.

On the graph for December 16, 1998, note the similarities and differences between the two plots shown. Pose two possible explanations for the difference(s) (if any). For each possible explanation, cite a piece of evidence that either supports or contradicts the explanation. Repeat for May 22, 1999 if your explanations and tests are any different for that day.

2. Compare the Hanford, CA observations of solar radiation intensity on a surface perpendicular to the sun's rays on May 22, 1999 with those on December 16, 1998. Pose two possible explanations for the difference(s) (if any). For each possible explanation, cite a piece of evidence that either supports or contradicts the explanation.

3. Compare the Hanford, CA observations of insolation on a horizontal surface at the top of the atmosphere on May 22, 1999 with those on December 16, 1998. Pose two possible explanations for the difference(s) (if any). For each possible explanation, cite a piece of evidence that either supports or contradicts the explanation.

(For your explanations and tests in Steps 1–3, try to use facts and/or ideas from the "Prior Knowledge Required" section of this lab, above, or data from Lab #2, Part I.)

Task B.1.c. (as defined in the Section B.1.c. above):

1. You have two graphs that each show plots of insolation on a horizontal surface at (a) the top of the atmosphere and (b) the earth's surface, observed at Hanford, CA. One graph shows these solar radiation intensity observations for the period from midnight to midnight on May 22, 1999 (standard time), while the other shows the same things from midnight to midnight on December 16, 1998.

On the graph for December 16, 1998, note the similarities and differences between the two curves. Pose two possible explanations for the difference(s). For each explanation, cite a piece of evidence that either supports or contradicts the explanation. (For your explanations and tests, try to use facts and/or ideas from the "Prior Knowledge Required" section of this lab, above.) (Repeat for May 22, 1999 if your explanations and tests of them differ from the ones for December.)

4. Rejoin your original team members, share your observations and possible explanation(s) with them, get feedback from them, and summarize your findings and ideas in writing, illustrated with the graphs.

1. Your team should prepare and turn in a single report that addresses the details of the instructions for all three tasks. Include all relevant graphs, labeled as needed so that you can refer to them easily in your report. Clearly identify who was responsible for each section of the report. (You can prepare each section of the report separately and simply staple them together, but every member of your group must approve of all sections.)

2. Your score for this lab will be based on how well the report as a whole addresses the instructions associated with each task (50%) and on how well you addressed your part of it in particular (50%). The score will depend on how thoroughly and clearly you address each instruction, how well you support possible explanation(s) that you propose to explain your observations, and on how well you test your possible explanations.