Download Factors Affecting Wind

Name _____________________________________________ Period: _________ Date: _________________
Factors Affecting Wind
Wind is created through differences in horizontal air pressure. Pressure can be visualized using
an isobar map, which shows lines of similar pressure. The pressure for each isobar is written in
millibars (mb). Without outside forces, wind flows at right angles to isobars from high pressure to
low pressure. This rule allows us to determine the direction of wind from looking at isobar maps.
Closely spaced isobars represent a higher difference in
pressure, which means higher wind speeds. Isobars
spaced farther apart indicate low wind speeds. The
spacing of these isobars over a certain distance shows
the pressure gradient.
Another factor affecting winds is the Coriolis effect.
Objects in motion appear to stray from their expected
path as the earth rotates under them. Objects in the
Northern Hemisphere are deflected to the right of their
intended path, and objects in the Southern Hemisphere
are deflected to the left.
The map below shows atmospheric pressure at sea level
for the eastern United States. Pressures are expressed
in millibars (e.g., 1020 mb). Using the map, answer
questions 1–6:
1. Directly on the map, draw a capital L in the center of a low pressure system, and draw a
capital H in the center of a high pressure system.
2. Four locations on the map are indicated by the capital letters A–D. Based on the information
on the map, which of these locations will experience the highest wind speed? (write letter in blank)
Highest wind speed: __________
3. Explain how you know which location will have the highest wind speed:
____________________________________________________________________________________
4. Find the location marked with an X on the map. At the location marked X, the wind will be
blowing (circle correct answer):
To the north
To the west
To the northwest
To the southeast
5. Explain how you know which direction the wind is blowing:
____________________________________________________________________________________
6. What are the highest/lowest air pressures represented on this map?
Highest air pressure: __________
Lowest air pressure: __________
Using the map below of the United States, answer questions 7–13:
D
A
X
B
C
7. Directly on the map, draw a capital L in the center of a low pressure system, and draw a
capital H in the center of a high pressure system.
8. Four locations on the map are indicated by the capital letters A–D. Based on the information
on the map, which of these locations will experience the highest wind speed? (write letter in blank)
Highest wind speed: __________
9. Explain how you know which location will have the highest wind speed:
____________________________________________________________________________________
10. Find the location marked with an X on the map. At the location marked X, the wind will be
blowing (circle correct answer):
To the north
To the west
To the northwest
To the southeast
11. Explain how you know which direction the wind is blowing:
____________________________________________________________________________________
12. What are the highest/lowest air pressures represented on this map?
Highest air pressure: __________
Lowest air pressure: __________
13. If you wanted to enjoy a nice sunny day, what part of the country would you fly to, and why?
____________________________________________________________________________________
Drawing Conclusions! Surface Air Pressure Map
This map shows the sea level pressures for various locations over the contiguous United States.
The values are in whole millibars (mb).
In this part of the exercise, you will be drawing isobar lines connecting identical values of sea level
pressure. Remember, these lines do not cross each other. Isobars are usually drawn for every 4mb,
using 1000mb as the starting point (e.g., 1000, 1004, 1008, etc., or 996, 992, 988, etc.). You will
then fill in details, as described by the procedures and analysis below.
You will need colored pencils in black, red, blue, green, yellow, and two other colors of your choice.
Procedure
14. Use a black colored pencil to begin drawing from the 1024mb station pressure over Salt Lake
City, Utah (in grey box). Draw a line to the next 1024 value located to the northeast (upper right).
Without lifting your pencil, draw a line to the next 1024 value located to the south, and then to the
one located southwest, finally returning to the Salt Lake City value. Remember, isobars are
smooth lines with few, if any, kinks.
The result is an elongated circle, centered approximately over eastern Utah. The line that was
drawn represents the 1024mb line. You can expect the pressure to be 1024mb everywhere along
that line. Repeat the procedure with the next isobar value. Remember, the value between isobars
is 4mb. As there are no 1028mb values on the map, your next line will follow the 1020mb reports.
Then continue with the remaining values until you have all the reports connected with an isobar.
You DO NOT need to connect lines that run off the map!
15. Label each isobar with the appropriate value. Traditionally, only the last two digits are used
for labels. For example, the label on the 1024 mb isobar would be 24. A 992 mb isobar will be
labeled 92. These labels can be placed anywhere along the isobar but are typically placed around
edges of the map at the end of each line. For closed isobars (lines that connect) a gap is placed in
the isobar with the value inserted in the gap. (See Ms. Nevel’s example on the board.)
Analysis
Isobars can be used to identify areas of “Highs” and “Lows.” The pressure in a High is greater
than the surrounding air. The pressure in a Low is lower than the surrounding air.
16. Label the center of the high pressure area with a large blue “H.” Label the center of the low
pressure area with a large red “L.”
High pressure regions are usually associated with dry weather because as the air sinks it warms,,
and the moisture evaporates. Low pressure regions usually bring precipitation because the air
cools as it rises, and the water vapor condenses.
17. Using the green pencil, shade in the general area(s) where you would expect to see rain or
snow.
18. Using the yellow pencil, shade in the general area(s) where would you expect to see clear skies.
In the northern hemisphere the wind blows clockwise around centers of high pressure. The wind
blows counterclockwise around centers of low pressure.
19. Using a new color, draw arrows around the “H” on your map to indicate the wind direction.
Using a different new color, draw arrows around the “L” on your map to indicate the wind
direction.
Assignment Analysis check list/rubric:
___ Isobar lines drawn in black
___ Isobar lines labeled with value
___ H location labeled in blue
___ L location labeled in red
___ Rain/snow area labeled in green
___ Clear area labeled in yellow
___ Wind direction arrows drawn around H in new color
___ Wind direction arrows drawn around L in other new color
___ Questions 1-12 completed, student’s name on paper