MET 1010 - Comments and Questions on Chapter 9

Chapter 9. The main theme in Chapter 9 is understanding why the winds blow in certain directions and how one can predict these directions. A major skill you need is an ability to read a surface-pressure isobar chart and an upper-level 500-mb or 300-mb contour chart and predict the wind patterns at each level. You are also expected to know the directions of the forces that create these winds. These includes the pressure gradient force, coriolis force and the friction force. You also need to know the way the forces vary with conditions. For example, recall that the coriolis force acts to the right of a person looking downwind in the Northern Hemisphere but to the left for a person in the Southern Hemisphere. The strength of the coriolis force is proportional to sin(latitude) and the wind speed. Finally, recall that since the friction force is unimportant at a height above 1 or 2 km, the result is pure geostrophic balance. A steep pressure gradient, which shows up on a surface or upper-level chart as closely spaced pressure or height lines, implies a relatively strong pressure gradient force and a correspondingly strong wind. We have gone over these concepts several times in class. If you can not understand these concepts, you need to review carefully or ask for help.
 

Chapter 9 - The Atmosphere in Motion

9-1. To monitor region-to-region variations in air pressure correctly, the most important correction to take into account involves differences in ___.

(1) temperature (2) altitude (3) density (4) gravity (5) humidity
 

9-2. Which one or more of the following are true when air aloft is relatively warm?
a) The 300-mb pressure surface is expected to be at higher altitude than normal.
b) At a given height aloft, pressure is likely to be lower than normal.
c) At a given height aloft, pressure is likely to be higher than normal.

(1) a (2) b (3) c (4) a and b (5) a and c
 

9-3. On a given day, a barometer at sea level reads a pressure of 30 inches of Hg. At the top of a 100 m tall building, what will be the new reading in inches of Hg for this same barometer? (Your book mentions that pressure falls about 10 mb/100 m near the surface.)
 

9-4. Which one or more of the following are true for a "column" of cold air relative to a "column" of warmer air?
a) The density is probably lower. b) Pressure must drop more rapidly with height.
c) The relative humidity must be lower.

(1) a (2) b (3) c (4) a and b (5) b and c
 

9-5. On a weather map, the largest pressure-gradient force occurs where the isobars ___.

(1) have the greatest curvature (2) indicate the highest pressure
(3) indicate the lowest pressure (4) have the greatest separation
(5) have the least separation
 

9-6. You are flying west-to-east on a day when the 500 mb chart shows contour lines that are oriented SW to NE between Texas and Chicago and then curve to the SE from Chicago to the Carolinas. In flying from Kansas to Virginia, you would expect to pass through a ___.

(1) geostrope (2) thermal low (3) pressure ridge (4) pressure trough (5) depression
 

9-7. For a wind that blows from out of the north in the Northern Hemisphere, the coriolis force at that instant is acting toward the ___ .

(1) S (2) E (3) W (4) NE (5) SE
 

9-8. Assume that the adjusted sea-level pressure decreases from east to west (high pressure to the east). Air is moving such that geostrophic balance is modified by friction forces. The direction of the pressure-gradient force is toward the ___.

(1) S (2) E (3) W (4) NE (5) SE
 

9-9. In the above question, the wind resulting from these conditions is a ___ wind.

(1) S (2) E (3) W (4) NE (5) SE
 

9-10. Which one or more of the following are true for a geostrophic wind?
a) the larger the pressure-gradient force at a given point, the larger the wind speed.
b) the higher the latitude for a given pressure-gradient force, the larger the wind speed.
c) The coriolis and pressure-gradient forces are equal and opposite.

(1) a (2) b (3) c (4) a and b (5) a and c
 

9-11. Train A moves directly westward at latitude 10° S. Train B moves at the same speed directly westward at latitude 40° N. Which one or more of the following are true?
a) The coriolis force on train B acts toward the north. b) The coriolis force on train A
acts toward the north. c) Train A has the larger coriolis force.

(1) a (2) b (3) c (4) a and c (5) b and c
 

9-12. At a point 45° N latitude, a high pressure zone lies to the south with isobar lines running east-west. The large-scale wind flow near the ground is expected to be from the ___.

(1) S (2) E (3) W (4) SW (5) SE
 

9-13. Which one or more of these are true for a "low" in the Northern Hemisphere?
a) Surface air is divergent b) Airflow is counterclockwise
c) The pressure force is smaller than the coriolis force.

(1) a (2) b (3) c (4) a and b (5) b and c
 

9-14. Which one or more of the following are true for a "low" in the Southern Hemisphere?
a) Winds rotate counterclockwise. b) Surface winds are divergent
c) Weather is likely to be cloudy.

(1) a (2) b (3) c (4) a and b (5) a and c
 

9-15. High surface pressure over an extended region implies which one or more of these?
a) surface divergence b) foul weather c) cyclonic air flow

(1) a (2) b (3) c (4) a and b (5) b and c
 

9-16. Air is flowing from east to west under pure geostrophic balance. This air then enters a region where the isobars curve toward the SE. Assuming the pressure gradient stays constant, the only way the air can continue to follow the isobars is for its speed to ___.

(1) decrease (2) stay the same (3) increase
 

9-17. Shown is a 500 mb contour chart over southeastern United States and is to be used for this and the next three questions. The most likely altitude for this chart is about ___ km.

(1) 3 1/2 (2) 4 1/2 (3) 5 1/2 (4) 7 (5) 10


 

9-18. The region of lowest altitude is at position ____.

9-19. The highest wind speed is probably at position ____.

9-20. The warmest air is probably at position ____.
 

ANSWERS TO CHAPTER 9 QUESTIONS:
 

25(29.7 inches)25 33355 14231 33ADC


To answer question 9-3, you can look at Fig. 9.4. Notice that a change of 10 mb is close to a change of 0.3 inches of Hg. Therefore, going upward 100 meters means a drop of 10 mb or 0.3 inches of Hg. The barometer will read 29.7 inches Hg at the top of the building.