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

(10 points)
(Lab Section 1: Wed., Feb. 15; Lab Section 2: Friday, Feb. 17)

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)
• zenith (the point infinitely far away directly overhead ["up"], directly opposite "down")
• perpendicular (at an angle of 90° to, at right angles to)
• normal (in the context of this subject, another word meaning perpendicular)
• horizontal (oriented in a direction perpendicular to down)
• horizon (the points far away where sky meets earth in the absence of obstructions)
• zenith angle (angle between the zenith and the sun)
• sun angle (angle between the sun and a horizontal surface)
• radiative intensity or flux (rate at which radiative energy strikes a unit of surface area)
• insolation (intensity of solar radiation striking a horizontal surface)
• midlatitudes (latitudes between 30° and 60°, in both hemispheres)
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, minimim, and average distance between the earth and the sun.
• The average intensity of solar radiation striking a surface directly facing the sun at the top of the atmosphere.
And finally, you should be able to:
• Identify three reasons why the intensity of solar radiation striking a surface might vary over time.
• Describe the relation between sun angle and insolation at the top of the atmosphere (at a given distance from the sun) (the "spreading out" effect).
• Describe the relation between distance from the sun and insolation (at a given sun angle).
• Describe the relation between sun angle and the distance that solar radiation travels through the atmosphere before reaching the earth's surface.
• Summarize the things that can happen to solar radiation as it passes through the atmosphere.
• Describe the relation between sun angle and insolation at the earth's surface, and the two contributing reasons for it.
Learning Objectives. After completing this activity, you should be able to:
• Identify ways in which insolation 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 attributes variations in temperature over the course of a day at least partly to variations in solar radiation (though of course there are other influences, too). Hence, we will start by exploring observations of solar radiation and try to make connections between those observations and observations of temperature at the earth's surface. In particular, in Lab #2, Part II, we will access, describe, and try to explain features of observed solar radiation data at several locations, 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 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 normal to (perpendicular to) the sun's rays (that is, directly facing the sun) and (ii) on a horizontal surface.

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

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.

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

1. You have been provided with 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 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, etc.)

2. You also have two plots of insolation 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 possible explanation(s) for the difference(s) (if any), citing any supporting evidence that you can think of. What other information (evidence) might help you test your explanation(s), and how would it help you test it (them)?

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 normal to the sun's rays and (b) on a horizontal surface, both at the top of the atmosphere, at 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 possible explanation(s) for the difference(s), and cite any evidence to support for your explanation(s) that you can think of. What information might help you test your explanation(s)? Repeat for May 22, 1999 if your explanation(s) and information to test the explanation(s) are any different for that day.

2. Compare the Hanford, CA observations of solar radiation intensity on a surface normal to the sun's rays on May 22, 1999 with those on December 16, 1998. Pose possible explanation(s) for the difference(s), if any. What information (evidence) might help you test your explanation(s), and how would it help you test it (them)?

3. Compare the Hanford, CA observations of insolation at the top of the atmosphere on May 22, 1999 with those on December 16, 1998. Pose possible explanation(s) for the difference(s), if any. What information (evidence) might help you test your explanation(s), and how would it help you test it (them)?

Task B.1.c. (as defined in the Section B.1.c. above):
1. You have two graphs that each show plots of insolation 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 one or more possible explanations for any differences, citing any supporting evidence that you can think of. For each explanation, what other information might help you test it, and how? Repeat for May 22, 1999 if your explanations and information to test them are any different for that day.

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 points above 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.