Sketching Assignment - Atmospheric Pressure, Circulation and Climate
A: Rising and Sinking Air and Differential Pressure
Underline 1 of each pair of bold words separated by /
1. When air is heated, it expands and becomes more / less dense, the pressure decreases / increases
and the air rises / sinks
2. When air is cooler than its surroundings it becomes more / less dense, the pressure decreases /
increases and the air rises / sinks
3. When air rises, it converges / diverges at the surface.
4. When air sinks, it converges / diverges at the surface.
This differential heating is what causes the lateral changes in atmospheric pressure which drives the
winds. Differential heating can result from changes in insolation, albedo, and heat capacity.
5. Insolation is the greatest at the equator / poles and therefore air rises / sinks at the equator and
rises / sinks at the poles. In the cross section below, sketch a simplified convection cell (known as a
Hadley cell) showing rising or sinking air at the equator and the poles and horizontal flow at the
surface and the upper troposphere. Indicate the location of High and Low pressure with an H and L
Top of Troposphere
Surface
Equator
South
Pole
North
Pole
6. Land has a much lower heat capacity than water and therefore heats / cools up more rapidly in the
day and heats / cools more rapidly at night. The resulting differential heating causes land and sea
breezes. In the two cross sections below, sketch the land sea convection cells showing rising or
sinking air and horizontal flow for both daytime and nighttime. Indicate the location of High and Low
pressure with an H and an L and indicate whether it is a sea breeze or a land breeze.
Daytime
Land
Sea
Nighttime
Land
Sea
1
B: Isobar Maps and the Pressure Gradient
The labeled lines on Figure 8 are examples of isobars, lines of equal pressure express in millibars (mb).
The gradient is greatest where the isobars are closely spaced. The hatched red, blue and purple lines are
fronts. Ignore them for now, we will examine them in next week’s lab.
A
B
Figure 8. Isobar map of North America. Isobars are in millibars. Source NOAA
7. What is the interval between the isobars on the map? __________________
8. Which of the points A, B, and C has the strongest winds? ____________
9. Which of the points A, B, and C has the weakest winds? ______________
10. Indicate on the map with an X where you think the weakest winds will be.
11. Using arrows, indicate the wind direction at A, B, and C assuming that only the pressure gradient is
responsible for the wind (no Coriolis effect)
C: Understanding The Coriolis Effect
On the rotating Earth, wind does not move in a straight line. To better understand the Coriolis Effect, we
will conduct the following experiment to see what happens to objects as they move across a rotating
Earth.
2
Spin a globe such that the sun rises in the east and sets in the west. If you do not have a globe, then use
an internet resource to answer the questions.
12. Observe it from the side. Does it rotate from east to west or west to east?
______________________
13. Observe the earth from above the north pole. Does it rotate clockwise or counter clockwise?
______________________
14. While continuing to spin the globe in the same direction, turn the globe upside down and observe
the globe from above the south pole. Does it rotate clockwise or counter clockwise?
______________________
15. On the diagram below, use arrows to indicate the direction of the winds around high and low
pressure centers in both the Northern and Southern Hemispheres.
Northern Hemisphere
H
Southern Hemisphere
L
H
L
16. Given what you have learned about wind circulation around high and low pressure centers due to
the Coriolis effect, using arrows, indicate the wind direction at points A, B, and C on Figure 8 in
section B
D: Global Circulation and climate
As discussed earlier and shown in Figure 6 (see Explain document), Global circulation establishes a set of
high and low pressure bands on the Earth’s surface:
 Low pressure near the equator
 A band of high pressure 30° N/S latitude
 Low pressure near 50°-60° N/S
 High pressure at the poles.
17. Draw on the map below the locations of high and low pressure over the oceans at the latitudes
indicated above.
18. Indicate the direction of the winds around the centers due to the Coriolis effect.
19. Use arrows to indicate the directions of the ocean currents. Use red to indicate warm currents and
blue to indicate cool currents.
20. Using the words Wet and Dry, indicate the climate at various positions over the continents.
3
30°N
30°N
0°
0°
30°S
30°S
21. Compare these results to your observations in Part 1 from the satellite image loop. Are they similar?
How?
4