Assignment 3: Seasonal and Daily Temperature Variations

Objectives: After successfully completing this lesson, you should be able to:

• identify basic variables and units of the x and y axes on an atmospheric thermodynamic diagram

• determine the location of the tropopause on a thermodynamic diagram

• create a graph from data of elevation and temperature, and calculate the resulting environmental lapse rate

Key Concepts :1. The average environmental lapse rate in the troposphere is approximately 6.5°C per km (or 3.6°F per 1,000 ft.).

2. The actual environmental lapse rate varies in time and space. The actual environmental lapse rate is routinely determined from radiosondes attached to weather balloons; the temperature data (in addition to pressure, humidity, and wind data) are transmitted to a ground station from the radiosonde as it ascends into the atmosphere. The data may be plotted on a graph known as a thermodynamic diagram.

3. Average surface temperatures generally decrease as latitude increases, but factors such as elevation, proximity to large bodies of water, ocean currents, and large-scale wind systems may cause deviations from this overall trend.

4. The 23.5º tilt of Earth's axis with respect to its orbital plane around the sun defines the significant latitudes: the Tropic of Cancer, Tropic of Capricorn, Arctic Circle, and Antarctic Circle.

Assignment work

1. From the American Meteorological Society Atmosphere Web site, view and print the temperature profile diagram (Stüve) for Dulles Airport, Washington, D.C. (IAD). (If IAD data are not available, use any station of your choice.) Answer the following questions and be sure to submit your printout.

a. What variables do the horizontal and vertical axes represent?

b. What are the units of the horizontal and vertical axes?

c. Which of the axes displays linear data; which displays nonlinear data?

d. What do the two black, plotted curves on the Stüve represent?

e. From the plotted air-temperature data, where is the tropopause (the boundary between the troposphere and stratosphere)? Explain.

2. Table 3.1 below lists elevation above sea level (in feet) and mean annual temperature (in °F) for several locations at approximately the same latitude along a line from centralTennessee eastward across the Appalachian Mountains to central North Carolina.

a. On a graph, plot the mean annual temperature along the y axis and elevation along the x axis for these stations.
Your points will not lie precisely on a straight line. Because air temperature generally decreases with elevation in the troposphere, however, the points should tend to orient themselves in a linear fashion. Draw a straight line of best fit to your plotted data and compute the slope of your line, thereby providing a numerical estimate of the average environmental lapse rate.

b. How close is your estimate to the average environmental lapse rate cited in Key Concept 1 of this lesson? (Hint: To draw a straight line of best fit through a set of points, think of the points as exhibits scattered in a large room of a museum. You want to get as close as possible to all the exhibits, but you are constrained to walk through the museum in a straight line. The most efficient path for you to accomplish your goal would be a good estimate of a straight line of best fit through the points.)

Table 3.1

3. Review your data and graph from Activity #1 of the lesson 2 lab. Based on your understanding of seasonal Earth-Sun geometry (Earth's axis tilt of 23.5º), at what latitude would you expect:

a. the greatest amount of radiation difference from winter to summer?

b. the greatest amount of temperature difference from winter to summer?

4. Using the instruments found in your "weather kit," take one daytime and one nighttime weather observation (or ob) of as many of the seven weather elements as you can (air temperature, air pressure, humidity, sky condition, wind speed and direction, precipitation, and visibility).

a. Record your obs in a simple text format, and then put it in "station model" format.

b. Indicate the location of your ob (city) and the time in both local and Z-time references.

c. Were there any data that you were unable to measure or observe at this time?

d. Discuss any differences or particular challenges between taking your day ob and taking your night ob.

e. If you are in the United States, immediately after taking your obs, go to the Weatherbug Web site. Call up the station closest to your location and record the current weather data. Compare the Weatherbug readings with your personal obs, and discuss possible reasons for the Weatherbug readings being different from yours.