METR 101-02 LAB LAB #6
Contouring Meteorological Data
(200 points total – Due 10/27/09)
Name:______
Reference Reading /The best reference on the art and science of contouring data is online, at a web site run by the University of Wisconsin at the following URL:
Use of contour maps
Contour analysis
Interpolation
Task 1
(no points, practice only)
Task 2
(100 points) / Introduction
Much of the introduction that follows is taken directly from the University of Wisconsin Web site referenced above.
To understand atmospheric conditions, you must be able to understand how variables (such as temperature, pressure, winds, and humidity) are changing in time and how they are changing with respect to one another. The weather map is a tool that aids this understanding. Various kinds of maps, or charts, are used to graphically depict these variables. A good map allows you to quicklyidentify patterns. For example, a weather map of forecasted high temperatures typically available in newspapers indicates the location of warm and cold regions of the country. From these maps you can quickly gage the predicted high temperature any place within the map.
Maps depicting weather and ocean conditions are drawn based on simultaneous observations made at many places throughout the world. Accurate portrayal of these observations is the key to a correct interpretation of the data. Meteorologists and oceanographers use a technique called contour analysis to visually explain the information the data is providing. Contouring data represents an elementary step in data analysis. Ability to correctly and confidently analyze data is critical to interpreting conditions.
An isopleth is a line of equal value (a Greek word iso – equal; pleth – value). Contouringis the process of drawing isopleths. A weather map contains isopleths of different weather parameters. For example, maps of temperatures have contours of constant temperature, or isotherms (iso-equal; therm-temperature). On these maps, anywhere along the 70 degree isotherm the air temperature is 70 degrees.
Contouring data can be difficult because observations are not made everywhere. Gaps in the observations exist and we must interpolate between the existing weather observations.
Lab Objectives
In this lab you will learn to draw contours on weather maps as a way of analyzing weather patterns. In the process you will learn the art of contour drawing.
Procedure
Spend some time practicing drawing contours using the interactive web site referenced above. We will practice drawing contours using this web site in class today.
The first map you will be turning in will be a simple surface isobar map. Notice that the pressure data is coded using the station model. Draw isobars in Figure 1 according to the convention used in the USA, which is every 4 millibars at pressure levels of 996 mb, 1000 mb, 1004 mb, etc. Make sure that your isopleths are smooth and neatly drawn and that the map is properly labeled. (20 points)
The next three surface maps will be used to contour the pressure every 4 mb, the temperature every 5 degrees, and the streamlines showing wind direction.
Metr 101 – Lab 4
Contouring Meteorological Data
Task 3 (50 points)Task 4 (50 points) / Refer to the maps of conditions at 500 mb over the contiguous US October 9 at 00Z. Use the one of the copies of the plotted map to draw isopleths of height every 6 decameters (at 540 dm, 546 dm, 552 dm, etc.) (Figure 2 - 25 points) and the other copy to draw isopleths of temperature (better known as isotherms) every 5 degrees Celsius at -5C, -10C, etc. (Figure 3 - 25 points). As in the first map you drew, make sure all your isopleths are drawn smoothly, accurately and neatly. Please, also make sure you label the maps in both Figure 2 and Figure 3 to indicate to the reader what kind of isopleths are provided.
Before you proceed, make sure you have drawn smooth and clearly labeled isopleths of the height and of the temperatures of the 500 mb surface in Figures 2 and 3. Now refer to these two figures to answer the following questions on a separate sheet:
a) Where are the lowest and highest values of 500 mb heights found on Figure 2? Where are the lowest and highest values of 500 mb temperatures found on Figure 3?
b) How would you describe the pattern of heights and temperatures that you see?
c) Are the patterns on the two figures similar? Is there a relationship between the height of 500 mb surfaces and the temperature of the 500 mb surface?
d) How does the spacing between height contours change in Figure2? Where are the strongest height gradients found? (Indicate by drawing a circle in Figure 2 in an area of strong height gradients using a coin (say, a quarter) as a guide?
e) Finally. Do you see a relationship between the height gradients and the strength of the wind? If so, what is it?