Ch. 16,  p. 466, #1-6, 8-15

1.  Summarize the processes by which water changes from one state of matter to another.  Indicate whether heat energy is absorbed or liberated.

A.  Heat is absorbed when ice changes to water (melting), when water changes to water vapor (evaporation), and when ice turns directly to water vapor without passing through the liquid state (sublimation).  Heat is liberated during condensation (the vapor-to-liquid phase change), freezing (the conversion of water to ice), and sublimation (the change from the vapor state directly to ice).

2.  After studying Table 15.1, write a generalization relating temperature and the capacity of air to hold water vapor.

A. As temperature increases, the capacity of air to hold water vapor increases (at an increasing rate).

3.  How do relative and specific humidity differ?

A.  Specific humidity incicates the amount of water vapor in the air and is expressed as the weight of water vapor per weight of air.

4.  Referring to Figure 15.6, answer the following questions and then write a generalization relating changes in air temperature to changes in relative humidity.
a)  During a typical day, when is the relative humidity highest?  Lowest?

A.  It is highest near sunrise and lowest during mid-afternoon.

b)  At what time of day would dew most likely form?

A.  When the temperature was lowest and the relative humidity highest, that is, near sunrise.

5.  If the temperature remains unchanged and the specific humidity decreases, how will relative humidity change?

A.  With a constant specific humidity, an increase in temperature causes a decline in relative humidity, and a drop in temperature causes a rise in relative humidity.

6.  On a cold winter day when the temperature is -10o C and the relative humidity is 50 percent, what is the specific humidity (refer to Table 15.1)?  What is the specific humidity for a day when the temperature is 20oC and the relative humidity is 50 percent?

A.  1 gram per kilogram of air; 7 grams per kilogram of air
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8.  Using the standard tables (Tables 15.2 and 15.3), determine the relative humidity and dew-point temperature if the dry-bulb thermometer reads 16oC and the wet-bulb thermometer reads 12o C.  How would the relative humidity and dew point change if the wet-bulb thermometer read 8oC?

A.  62% relative humidity; dew point 9o C; 29% relative humidity; dew point -1oC

9.  On a warm summer day when the relative humidity is high, it may seem even warmer than the thermometer indicates.  Why do we feel so uncomfortable on a "muggy" day?

A.  Since the relative humidity is high, there would be a minimum of evaporation of perspiration, the body'g natural cooling system.

10.  Why does air cool when it rises through the atmosphere?

A.  As air rises, it expands because air pressure decreases with an increase in altitude.  When air expands, it cools adiabatically.

11.  Explain the difference between environmental lapse rate and adiabatic cooling.

A.  The environmental lapse rate refers to the temperature drop with increasing altitude in the troposphere; that is the temperature of the environment at different altitudes.  It implies no air movement.  Adiabatic cooling is associated only with ascending air, which cools by expansion.

12.  If unsaturated air at 23oC were to rise, what would its temperature be at 500 meters?  If the dew point temperature at the condensation level were 13oC, at what altitude would clouds begin to form?

A.  18oC (because of the dry adiabatic rate);  1000 meters.

13.  Why does the adiabatic rate of cooling change when condensation begins?  Why is the wet adiabatic rate not a constant figure?

A.  When condensation occurs, latent heat is released by the vapor/water droplets into the surrounding air.  This heats up the surrounding air, countering some of the cooling defined by the dry adiabatic rate.  The wet adiabatic rate depends on the quantity of vapor in the air.

14.  The contents of an aerosol can are under very high pressure.  When you push the nozzle on such a can, the spray feels cold.  Explain.

A.  When you push the nozzle on the aerosol can, pressure in the can decreases as the contents begins to escape the can.  The drop in pressure results in adiabatic cooling.

15.  How do orographic lifting and frontal wedging act to force air to rise?

A.  In orographic lifting, a mountain side serves as a barrier to cause air to ramp up.  In frontal wedging, a cold mass of air acts as a barrier forcing warmer air to ramp up and rise.


 Last update 3/12/2004
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