Physics 137 - Introduction to the Atmosphere and Weather                                    Homework Key - Assignment #10

Revised  11/02/2009

10-QT4. Why is the difference in surface wind speed between morning and afternoon typically greater on a clear, sunny day than on a cloudy,
               overcast day?

On a clear, sunny day, the surface and adjacent air is heated more by the sun than on a cloudy day, causing a thicker layer of unstable air near the surface. This thicker unstable layer leads to more extensive mixing with air in higher layers than on a cloudy day. Since the greater horizontal momentum in higher layers is preserved as that air is mixed with lower layers, and since that greater horizontal momentum is manifest as higher surface wind speed, that speed is greater in the afternoon (when mixing typically reaches a maximum) on a clear day than on a cloudy day.

 

10-QT6. Average annual wind speed information in knots is given here for two cities located on the Great Plains. Which city would probably be the
               better site for a wind turbine?  Why?

 

Time
  12 am 3 6 9 Noon 3 6 9 Average Annual Wind Speed [Knots]
City A 12 7 8 13 15 18 14 13 12.5
City B 8 6 6 13 20 22 15 10 12.5

 

City A is the better site. The winds here are steadier and also strong enough to make electricity throughout the 24-hour day.

 

10-QT9. Why do clouds tend to form over land with a sea breeze and over water with a land breeze?

The convective loop associated with a sea breeze is characterized by uplift over land and subsidence over water, thus associated clouds tend to form over land. A land breeze, on the other hand, is characterized by uplift over the sea and subsidence over land. Thus the associated clouds tend to form over the sea.

 

10-QT11. If campfire smoke is blowing uphill along the east-facing side of the hill and downhill along the west-facing side of the same hill, are the fires
                cooking breakfast or dinner? From the drift of the smoke, how were you able to tell?

The fires are cooking breakfast. In the early morning the east face of a hill absorbs more energy from the sun than the west-facing slope. Thus uplift associated with surface heating begins on the east face while the west face is still turned away from the sun and cooling radiatively leading to longer persistence of the nighttime drainage (downward) flow.

 

10-PE3. On the map of the United States, label where each of the following winds might be observed, then show with arrows the general direction of
              air flow that occurs with each of the winds. (a) Santa Ana wind, (b) chinook wind, (c) California norther, (d) northeaster, (e) Columbia gorge
              wind (downslope), (f) Texas norther (blue norther), (g) sea breeze along the New Jersey shore, (h) sea breeze in Los Angeles, California.

Refer to the figure below.

10-PE4. On the same map of the United States, show where the centers of atmospheric pressure should be located in order to produce the following
              winds. Place a large L on the map for the center of low pressure and a large H for the center of high pressure. (Be sure to place the letter
              representing the wind next to the L or the H.) (a) high-pressure are for a Santa Ana wind, (b) low-pressure area for a chinook wind, (c) high-
              pressure area for a northeaster, (e) high-pressure area for a Columbia gorge sind (downslope wind), (f) high- and low-pressure areas for a
              Texas norther (blue norther), (g) high-pressure area for a sea breeze along the New Jersey shore, (h) low-pressure area for a sea breeze in
              Los Angeles, California.

Refer to the figure above.