Midterm Exam Solutions | Physical Meteorology | AOSC 400, Exams of Meteorology

Download Midterm Exam Solutions | Physical Meteorology | AOSC 400 and more Exams Meteorology in PDF only on Docsity!

AOSC400 Midterm Examination Solution October 29, 2008

This is a 50minute closed book examination consisting of 10 multiple choice questions (~1min each) and one short essay (~10min). Please relax. Then look over the whole examination before beginning.

Part 1 (1pt each)

1. Lines connecting points of equal pressure are called: a. isobars. b. millibars. c. contours. d. isotherms. e. a coordinate grid.

ANSWER: a

2. Low on a constant height chart corresponds to low on a constant pressure chart. a. pressures; pressures b. pressures; heights c. heights; pressures d. heights; heights

ANSWER: b

3. The surface pressures at the bases of warm and cold columns of air are equal. Air pressure in the warm column of air will with increasing height than in the cold column. a. decrease; more rapidly b. decrease; more slowly c. increase; more rapidly d. increase; more slowly

ANSWER: b

4. Which of the following forces can not act to change the speed of the wind? a. pressure gradient force b. frictional force c. Coriolis force d. none of the above

ANSWER: c

5. Subsidence inversions are best developed with pressure areas because of the ___________ air motions associated with them. a. high; rising b. high; sinking c. low; rising d. low; sinking

ANSWER: b

6. If the environmental lapse rate is less than the moist adiabatic rate, the atmosphere is: a. conditionally unstable. b. absolutely stable. c. absolutely unstable. d. neutrally stable.

ANSWER: b

7. Which of the following conditions would be described as the most stable? a. Environmental lapse rate is 13 oC per kilometer. b. Environmental lapse rate is 3 oC per kilometer. c. isothermal conditions d. an inversion

ANSWER: d

8. Polar orbiting satellites: a. remain above a fixed point over the North or South Pole. b. pass directly over the same place on each orbit. c. on each successive orbit view an area to the west of the previous orbit. d. follow a line of constant latitude around the earth.

ANSWER: c

9. Lenticular clouds typically form _______________ a mountain range. a. downwind of b. upwind of c. far away from d. about 10 km above

ANSWER: a

10. If the air temperature remains constant, evaporating water into the air will the dew point and the relative humidity. a. increase; increase b. increase; decrease

c. decrease; increase d. decrease; decrease

ANSWER: a

Part 2 (10pts each)

1. Suppose air in a closed container has a pressure of 1000mb and a temperature of 20oC. a) Use the gas law to determine the air density in the container [R=2.87 (mb m3)/(K kg)]. b) If the density in the container remains constant, but the pressure doubles what would be the new temperature?

(a) density = 1.19 kg/m (b) Within the container, an increase in pressure must be caused by an increase in temperature. New temperature = 586 K.

2. Please identify the type of cloud shown in Figure 1. Please briefly discuss the processes involved in different parts of the cloud (use arrows to indicate the part of the cloud you are discussing.

Figure 1 : a cloud

This is a photograph of a cumulonimbus cloud. Notice the anvil cloud (upper left) which may extend to 10km altitude or beyond, contains ice crystals, and takes its shape from high level winds blowing to the left in this picture. Note the central column with strong uplift and indication of rain below the lowest cloud level.

3. a) Under what conditions (if any) might you record a station pressure of 750 mb? b) If the earth were to begin rotating in the other direction, would air still rise in the center of

surface low pressure?

a) Standard sea level pressure is 1015 mb. Pressure decreases with height approximately exponentially as p(z)=1015*e-(z/8.5km). Plugging in P(z)=750mb gives z=2.5km height. So, 750mb is the pressure we might expect to find in Vail, Colorado for example. Incidentally, the lowest surface pressure associated with a hurricane was Wilma at 882mb. b) Air would still rise at the center of a surface low pressure. Incidentally, the Southern Hemisphere behaves kind of like the Northern Hemisphere, only with reversed rotation (in other words, the Coriolis force is negative).

4. Explain the processes by which cloud droplets grow large enough to rain. What is ‘collision and coalescence’? What is the Bergeron Process?

Two processes describe the growth of rain drops:

1. Collision and coalescence : Cloud droplets collide with each other. If they stick to each other, or coalesce, the drop grows. The faster the droplet descends the more collisions can be expected. This process is most important in the tropics and when rain drops are already big. For smaller droplets the most important process is:

2. The Bergeron process depends on the fact that the saturation vapor pressure with respect to ice is less than the saturation vapor pressure with respect to water. Pure water droplets freeze only at temperatures of -40°C. Tor Bergeron realized that as air reaches saturation and a mixture of water and ice exists at the same time then the difference in vapor pressures will cause the water droplets to evaporate and the ice crystals to grow through sublimation.