Contouring

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Contouring
AOS 101 Section 301 2 February 2009
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Contouring

• Rather than representing meteorological data as a
  set of separate points

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Contouring

• It can be described as contours lines of
  constant value

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Contouring

• It can be described as contours lines of
  constant value (shaded)

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Contouring

• When contouring, we are assuming that the
  atmosphere is continuous there are no sudden,
  abrupt changes over short distances

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Contouring

• In a continuous fluid like the atmosphere, when
  we see two different observations separated by
  some distance -

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Contouring

• - we assume that values in the intermediate space
  between those observations will progress from one
  observation to the other

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Rules of Contour Analysis

• 1) Contours do not abruptly begin or end in the
  middle of the plot

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Rules of Contour Analysis

• 1) Contours do not abruptly begin or end in the
  middle of the plot

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Rules of Contour Analysis

• 1) You can backtrack, loop around, and make
  closed loops in the plot

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Rules of Contour Analysis

• 2) Lines cannot cross each other

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Rules of Contour Analysis

• 2) Lines cannot cross each other

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Rules of Contour Analysis

• 2) You can have multiple contours of the same
  value on the same plot

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Rules of Contour Analysis

• 2) You can have multiple contours of the same
  value on the same plot

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Rules of Contour Analysis

• 3) Contours do not branch or fork from one
  another they are a single, continuous line or
  loop

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Rules of Contour Analysis

• 3) Contours do not branch or fork from one
  another they are a single, continuous line or
  loop

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Rules of Contour Analysis

• 3) Contours do not branch or fork from one
  another they are a single, continuous line or
  loop

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Rules of Contour Analysis

• 3) Again, use of multiple contours and closed
  loops can help you avoid these problems

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Rules of Contour Analysis

• 3) Again, use of multiple contours and closed
  loops can help you avoid these problems

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Rules of Contour Analysis

• 4) Always label your contours
• 5) Contour at evenly-spaced intervals
• 6) Do not allow contours to stray into regions
  where there is absolutely no data (e.g. oceans)

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Helpful Hint

• Think about the contour as a line separating the
  observations with higher values on one side of
  the line, and lower values on the other side

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Helpful Hint

• Think about the contour as a line separating the
  observations with higher values on one side of
  the line, and lower values on the other side

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Draw the 25-line
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Helpful Hint

• Think about the contour as a line separating the
  observations with higher values on one side of
  the line, and lower values on the other side

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Draw the 25-line
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Helpful Hint

• Think about the contour as a line separating the
  observations with higher values on one side of
  the line, and lower values on the other side

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Draw the 25-line
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Helpful Hint

• Think about the contour as a line separating the
  observations with higher values on one side of
  the line, and lower values on the other side

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Draw the 30-line
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Helpful Hint

• Think about the contour as a line separating the
  observations with higher values on one side of
  the line, and lower values on the other side

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Draw the 30-line
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Helpful Hint

• Think about the contour as a line separating the
  observations with higher values on one side of
  the line, and lower values on the other side

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Draw the 30-line
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Helpful Hint

• Think about the contour as a line separating the
  observations with higher values on one side of
  the line, and lower values on the other side

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Draw the 20-line
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Helpful Hint

• Think about the contour as a line separating the
  observations with higher values on one side of
  the line, and lower values on the other side

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Draw the 20-line
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Helpful Hint

• Think about the contour as a line separating the
  observations with higher values on one side of
  the line, and lower values on the other side

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Draw the 20-line
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Commonly Seen Contour Plots

• Here are some commonly seen contoured variables,
  and their names

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Sea-Level Pressure (Isobars)
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Temperature (Isotherms)
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Wind Speed (Isotachs)
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Want Some Practice?

• Professor Steve Ackerman has developed a website
  which allows you to practice contour analysis
  through a Java-applet
• http//profhorn.meteor.wisc.edu/wxwise/contour/con
  tour1.html

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Your Homework

• Using a plot of surface temperatures for the
  morning of January 24, 2009 (provided), create a
  contour analysis of surface temperature every 6
  degrees divisible by 6 degrees (e.g. -12, -6, 0,
  6, 12, etc.)
• Suggestion Start with the zero-line, then do
  positive values in order (6, 12, 18, etc.), then
  do negative values in order (-6, -12, -18, etc.)

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-12?
-4?