Seasonal Temperature Changes

Introduction. Climate at a particular place is defined in terms of the (1) average, (2) extremes (record maximum and minimum), and (3) degree and character of the variability of the weather over many years. When we look closely at the variability of weather at any particular place, we find that it exhibits a combination of both random and regular (periodic) variations, on time scales that range from fractions of a second to many millions of years.

Ignoring the often large random variations that weather exhibits and considering only regular, periodic variations, at most places we notice daily variations (the diurnal cycle) and seasonal variations (the seasonal cycle) the most. (Longer-term periodic variations can be quite large—Pleistocene glacial and interglacial periods, for example—but the time scale for those is far greater than a human lifetime, so we don't notice them directly.)

In this lab activity, we will investigate some aspects of seasonal variations in temperature, in particular how seasonal temperature variations vary from place to place globally. (Note: variations over time are temporal variations; variations from place to place are spatial variations.)

Objectives. By the end of this lab activity, you should be able to:

• pose and answer questions about plotting conventions for spatially varying data such as temperature recorded at a given time;
• describe and compare the patterns shown on such plots for data recorded at different times
• identify ways to visualize temporal variations in spatial plots (of quantities such as air temperature)
• interpret such visualizations

Materials needed:

• My World GIS 4.1 software (installed on computers in TH 604, 607, 513, and 518 and available for free 45-day trial from Pasco)
• Monthly average surface air temperature data sets for 1982-1994 (installed with My World GIS 4.1 in TH 604, 607, 513, and 518)

Instructions and Questions.

(A) Getting Started

1. On one of the our lab computers, locate the My World GIS icon on the Dock (the row of icons at the bottom of the screen). (It consists of a blue and green earth.) Click on it to run the software. You'll get a "Welcome to My World GIS" window; in that window, click on the "Get Started" button. Click on the green button in the upper-left-hand corner of the My World GIS window (so that it fills the computer screen).
   
   
2. Pull down the "File" menu and select "Open Project...". You'll get an "Open Project" dialog window.
   
   
3. Click on the "Home" button (showing an icon of a house), navigate to Courses > E535 > Class, select (highlight) the file "SeasonalTemperatureVariations.m3vz", and click on the "Open" button.
   
   

(B) What Am I Looking at?

1. You should see a colorful plot (a visualization of data) on a map of the world. What does this visualization show? (Try to identify as much specific information about what the plot shows as you can.)
   
   
2. Zoom in on any spot on the plot. What do you see? What does this suggest about the nature of the data and about the way in which the visualization has been designed? (Note: This type of plot is called a color-shaded plot.)
   
   
3. In the left-hand ("Layer List") sub-window of the My World GIS window, click on (highlight) the panel labeled "MonAvg_SurfaceTemperature.wwf". Then click on the "Edit the Appearance of the Active Layer" icon (the paper & pencil icon at the top of the Layer List sub-window). This opens a dialog window. Based on what you see in this dialog window, what more can you say about how the visualization has been designed? (Make note of some of the key aspects.)
   
   
4. Close the 'Edit Appearance of Layer" dialog window (click on the red button in its upper-left-hand corner).
   
   
5. Make the plot fill the main display screen (click on the "Zoom to All" icon above the plot; note that this is not the same as the "Zoom In Tool" icon in the same row of icons).
   
   
6. Identify what you consider the handful of main features of the pattern shown by the plot.
   
   

(C) Comparing Two Plots

1. Pull down the "Windows" menu and select "New Child Window...". This should open a "Child Window" that displays the same plot as the main display window.
   
   
2. In the Layer List sub-window, in the "Mon_Avg_SurfaceTemperature.wwf" panel, pull down the "Surface Temperature..." menu to get a list of data sets that you can display in the main display window. Select "Surface Temperature 1982-07-Jan.wwf". This should create a new plot in the main display window.
   
   
3. Repeat Step B.3 above. Note the information about how this color-shaded plot has been designed. Does it differ from the other plot? Why might we care whether it differs or not?
   
   
4. Identify what you consider the handful of main features of the pattern shown by the plot.
   
   
5. Repeat Step C.1 above. Arrange the two open child windows so that they are side by side, about the same size, and are as large as you can make them and still see the plots.
   
   
6. Make each of the plots in the child windows fill their respective windows.
   
   
7. Identify what you consider to be main ways in which the two plots are similar.
   
   
8. Identify what you consider to be the handful of main differences between the two plots.
   
   

(D) Better Ways to Compare the Two Plots?

1. What might be one or two better ways to show the differences between the two plots?
   
   
2. In the "MonAvg_SurfaceTemperature" panel in the Layer List sub-window, pull down the menu of data sets and select "Jul - Jan 1982 Sfc Temp Difference" (near the bottom of the long list). What does this plot show? How is the visualization designed?
   
   
3. Identify a handful of what you consider to be the more significant features of the pattern shown by the plot. What do these features tell you? (Note: For our purposes here, you don't have to explain the physical causes of any features, though you might be tempted to—just discern and describe the features and perhaps interpret them at a level more descriptive than causal).