LEAD-TO-LEARN
EXPLORING TEMPERATURE CONTRASTS THROUGH
VISUALIZATIONS
WORK SHEET
In this activity you will visualize temperature data from a numerical model and
use it to explore the relationship between temperature contrasts, weather
patterns, and geographical features.
PART A: Generating the visualization
a. Launch IDV
b. Four windows should appear: 1) The Display Window, 2) The Data Selector
Window, 3) Parameter Control Window, and the User’s Guide.
PART B: Orienting and Problem Solving with IDV
a. You will notice that there are regions where the temperature contours are
spaced closely together (strong gradients), and others where they are
spread far apart (weak gradients).
Strong gradient
Weak gradient
To better visualize these gradients, go to the Parameter Control Window,
click the contour “SET” button, and reset the contour interval to 2.0 Celsius.
You will notice that a greater number of temperature contours (isotherms)
appear in the display window.
In the top right corner of the display window, click the forward arrow to
animate the display. Observe the animation through several loops.

Do you observe regions where the location of the strong gradients
remains relatively stationary over particular geographical features?
To help identify regions by state boundaries, click on “Background Maps” in
the upper right frame in the display window, and activate “Hi-Res US.”

Are these contrasts associated with geographical features (e.g.,
mountain ranges, coastal areas)?

Can you explain why geographical features have an influence on the
properties of the atmosphere?
b. Again, animate the visualization of temperature, but this time, concentrate
on the shape of this band of temperature contrasts.

What pattern does it most often assume as it tracks across the U.S.?
(Here it may be helpful to click through the visualization one frame at
a time, and stop when you get to a frame that shows a particularly
clear and coherent pattern.)

Can you suggest why this might be preferred pattern for the behavior
of the atmosphere?

What can you say about the movement of the regions of strongest
temperature gradients from one forecast period to the next?

Can you think of mechanisms or processes that may be responsible
for the contrasts (gradients) seen in the modeled temperature field?

What do you think we might call this band of contrasts as it passes
over us at the surface?
c. IDV features the ability to visualize temperature and multiple vertical levels.
These levels are called isobaric surfaces, or constant pressure surfaces.
Bring to front the Parameter Control Window and notice that the
temperature you are currently visualizing is at 1000 hPa, which close to the
surface. Since pressure decreases with height, we can use the IDV to
investigate how the region of temperature contrasts change as the pressure
decreases, or the altitude increases. The change in pressure with altitude is
called an inverse relationship because as pressure decreases altitude
increases.
HectoPascals are units of pressure. Air Pressure is the downward force
exerted by the weight of air in a column, divided by the area over which
the force is exerted. One hectoPascal = 100 Pascals = 100 kg m -1s-2. The
units of kg m-1s-2 come from the ratio of force (F-mass x acceleration = kg
m s-2) divided by area (m2). Taking the ratio gives kg m s-2/m2 = kg m-1s-2,
the unit of pressure. This unit is called a Pascal after Blaise Pascal, a 17th
century scientist and mathematician.
Starting with temperature on the 1000 hPa isobaric surface, which is like
saying the temperature near the Earth’s surface, pick a region of particularly
sharp temperature contrasts, one which is not associated with a
geographical feature (see Part B.a). Bring forward the Parameter Control
Window and place it alongside the Display Window. Change the level from
1000 to 850 hPa in the Parameter Control Window, and comment on the
changes that you observe over the region you had previously selected.
Continue to change the level from 850 to 700 to 500 to 300 hPa, and
comment on the in the intensity and location of the sharp gradients. (Later
project – compare winter verses summer). You can view the how the levels
are changing by holding down the right mouse button while moving the
mouse to reveal the 3-D aspects of this visualization.

How does the location of the strong contrasts change with respect to
the latitude and longitude as the height increases? (Move the cursor
to the center of the strong gradients each time you change the
pressure level and record the latitude and longitude of this center
point.)

Can you explain why the strongest contrasts tilt in this manner?

Are the temperature gradients stronger or weaker with increasing
altitude?
PART C: Higher level visualizations
a. Students are asked to bring in another parameter, look for relationships as
they did with temperature, and in addition, the new parameter’s relationship
with temperature. Examples are relative humidity (see below), dew point,
wind velocity, etc.
b. Vertical cross-sections are slices through the atmosphere at a given
moment in time. To view a vertical cross-section, on the Data Selector
Window choose file > import, then select bundle1.xidv. IDV will load the preconstructed bundle, which includes a vertical cross-section. You can move
the cross-section by pointing to the center marker on the cross section and
holding down the left mouse button while moving the mouse. You can rotate
the cross-section by doing the same to the makers at the located at the
ends of the cross-section.