Contouring

Purpose:

To analyze a surface level pressure map.

Equipment:

A pencil with a good eraser, surface map with pressure observations.

Background:

As discussed in class, atmospheric pressure is equal to the weight of all the air in the column above you. For atmospheric applications this is measured in units of millibars (mb). Pressure is measured by instruments called barometers. These pressure observations are then used by meteorologists to gain insight into the locations of weather phenomena such as storms or fair weather. A simple and common way that meteorologists show the pressure information is by creating contour maps, which show the locations of pressure maxima and minima. In this lab we will be doing just that.

Procedure:

The process of producing a contour map is really just a more complicated form of connecting the dots. Draw smooth lines between the points that are labeled with the same pressure. Usually the values at nearby observing stations will not have exactly the same value. You will need to interpolate between points to determine where your contour lines will go. This will be explained in more detail in the quiz section.

1. On the map, we have drawn some sample pressure contours. Fill in the blanks for the pressure contours using 4 mb intervals (for example, draw the contours for 996 mb, 1000 mb, 1004 mb, and so on).

2. Label the locations of the low pressure center with a capital "L".

Guidelines for contouring:

General

1. Use a pencil with a good eraser. Draw the initial lines faintly. Go back over your contours once you are happy with your analysis to thicken and darken them.

2. Remember to draw contours at the specified intervals.

3. Do not draw contours far beyond where there is data.

4. Contours do not fork.

5. Remember to label contours.

6. Values are higher on one side of the contour and lower on the other side.

7. Contours pass through stations that have the same value.

8. Draw contours smoothly.

Rules for drawing isobars

(Isobar: "iso" means "same"; "bar" refers to pressure; therefore an isobar connects points of equal pressure)

1. All points on an isobar have the same pressure. Draw a line through a specific data point only if it has the exact pressure of that isobar.

2. Each isobar has a higher value side and a lower value side.

3. Isobars never cross.

4. Isobars either form closed curves or go off the edge of the map. They don?t end in the middle of the map.