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part 1:  Mapping Air Pressure

Read Appendix B, "Isolines" and Appendix C, "Profile Construction" before attempting Part 1.

1.   Draw isobars on the map in Figure 4.5 every 4 millibars, starting with a low of 1000 mb and ending with a high of 1036 mb.  Be sure to label each isobar so that the pattern is clear and easy to see.

2.   Where do you find centers of high pressure?    COLORADO, UTAH

3.   Where do you find centers of low pressure?    ONTARIO, NEW YORK

4.   Label these high and low pressure centers on the map with an "H" or an "L".

5.   On the graph paper, draw a profile of the pressure gradient from point X, on the west coast, to point Y, one the east coast.  Be sure to label the axes properly.

6.   In general, wind tends to blow from areas of HIGH pressure to areas of LOW pressure.

7.   Although differences in atmospheric pressure are the driving force causing winds to blow, winds rarely flow directly down the pressure gradient because the earth rotates. As a result of the Coriolis force, winds appear to be deflected.  Draw several arrows indicating wind direction in and around the high and low pressure centers on your atmospheric pressure map.

8.   What are the wind speeds and directions at the following stations on January 3, 1988 (Figure 4.6)?

              Station                                Wind Direction                Wind Speed

           Dodge City, Kansas             NNW (350)                    15 (kts)

           Wausau, Wisconsin            ESE (115)                         5

           Abilene, Texas                     SSE (165)                         10

           Bismarck, North Dakota      WNW (285)                    20

 

 

 

 

 

Text Box: FIGURE 4.6 January 3, 1988 Weather MapAdobe Systems 



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part 2:  Seasonal Pressure Gradients and Wind Speed

Use the January 3, 1988 (Figure 4.6) and July 3, 1991 (Figure 4.7) maps to answer the following questions.

1.   Record the wind speed, in knots, for each of the four stations below using the January 3, 1988 weather map (Figure 4.6).  Use the following generalization:

            no feather = 0 knots                      full feather = 10 knots

            half a feather = 5 knots                  triangle = 50 knots

Station O    20 knots (Bismark ND)               Station Y    10 knots (Minneapolis MN)

Station P     15 knots (Pierre SD)                   Station Z    5 knots (Wausau WI)

2.   Record the wind speed for the same 4 stations as they appear on the July 3, 1991 map (Figure 4.7).

Station O    10 knots (Bismark ND)               Station Y    5 knots (Minneapolis MN)

Station P     10 knots (Pierre SD)                   Station Z    5 knots (Wausau WI)

3.   Determine the average wind speed for each map using only the four stations above.

a.   January 3, 1988 average wind speed = 12.25 KTS

b.   July 3, 1991 average wind speed = 7.25 KTS

4.   Examine these two weather maps.  Which month experienced steeper pressure gradients?

JANUARY

5.   What evidence from the maps did you use to support your answer to question 4?

CLOSER ISOBAR SPACING

6.   a.   Do the average wind speeds for each map help substantiate your answer to question 4?

b.   How? Stronger winter winds derive from steeper pressure and temperature gradients

7.   a.   Which season probably had the steeper latitudinal temperature gradient? WINTER

b.   Why? NORTH-SOUTH TEMPERATURE DIFFERENCES ARE GREATER. 

GREATER PRESSURE IMBALANCES (INDICATED BY CLOSER ISOBARS) RESULT FROM GREATER HEATING/COOLING IMBALANCES WITHIN THE SAME AMOUNT OF AREA

 

Text Box: FIGURE 4.7 July 3, 1991 Weather MapAdobe Systems