Lab 5:Atmospheric Moisture
Subject is natural environments the atmosphere
SECTION 5.1 – ATMOSPHERIC MOISTURE AND PHASE CHANGES OF WATER
By observing, recording and analyzing weather conditions, meteorologists attempt to
define the principles that control the complex interactions that occur in the
atmosphere. Use Figure 1 to answer questions 1-4.
Figure 1. Changes of state of water.
1. To help visualize the processes and heat requirements for changing the state of
matter of water, write the name of the process involved (choose from the list below)
and whether heat is absorbed or released by water during the process at the
indicated location by each arrow in Figure 1. [12 pt]
Freezing
Evaporation
Deposition
Sublimation
Melting
Condensation
2. To melt ice, heat energy must be (absorbed, released) by water molecules. [1 pt]
3. The process of condensation requires that water molecules (absorb, release) heat
energy. [1 pt]
4. The energy requirement for the process of deposition is the (same as, less than)
the total energy required to condense water vapor and then freeze the water. [1 pt]
Latent Heat Experiment
This experiment will help you gain a better understanding of the role of heat in
changing the state of matter. You are going to heat a beaker that contains a mixture
of ice and water. You will record temperature changes as the ice melts and continue
to record the temperature changes after the ice melts. Conduct the experiment by
completing the following steps:
5. Prior to starting the experiment, write a brief hypothesis of how you think the
temperature of ice-water mixture will change when heat is added. Use your
knowledge of phase changes and latent heat to help with your hypothesis. [1 pt]
Step 1: Turn on the hot plate and set the temperature dial to about three-quarters
maximum strength (7 on a scale of 10).
Step 2: Fill a Mason jar approximately half full with ice and add enough COLD water
to cover the ice. Insert a temperature through the hole in the Mason jar’s lid.
Step 3: Gently stir the ice-water mixture in the Mason jar. After 15 seconds, record
the temperature of the mixture. This is the “starting” temperature at time 0. Record
this value in an Excel table. (If you did not bring your laptop, record temperatures on
a piece of paper and entered into Excel after lab).
Step 4: Place the Mason jar with the ice-water mixture on the hot plate and while
stirring constantly, record the temperature of the mixture at one minute intervals.
Record all temperatures in your Excel table. Students will take turns reading the
temperature of the ice-water mixture. Continue until ice has completely melted. Note
this time in your Excel table.
Step 5: Continue stirring the mixture and recording the temperature for five minutes
in one minute intervals after the ice has melted. Record all temperatures in your
Excel table. Be sure you get all temperatures before leaving lab!!
Step 6: In Excel, make a graph of the temperature pattern of the ice-water mixture
over time. Perform this analysis on one graph with a line plotted including the data
points). Be sure to label your axes and include a title of the experiment. Include
both the table and graph with your submitted lab! [6 pt, 3 pt for table and 3 pt for
graph]
6. How did the temperature of the mixture change prior to, and after, the ice melted.
Describe the trend you plotted in your graph. [2 pt]
7. Calculate the average temperature change per minute of the ice-water mixture
prior to the ice melting and the average rate after the ice had melted. [2 pt]
Average rate prior to melting: __________________________________
Average rate after melting: _____________________________________
8. With your answers to question 6 and 7 in mind, write a statement comparing the
results of this experiment to your initial hypothesis. Explain. [1 pt]
9. With reference to the absorption or release of latent (hidden) heat, explain why
the temperature changed at a different rate after the ice melted as compared to
before all the ice had melted. [2 pt]
SECTION 5.2 – WATER–VAPOR CAPACITY OF AIR
Table 1 presents the mixing ratios of saturated air (water vapor needed for saturation) at various temperatures. Use the table to answer questions 10-13.
Table 1. Amount of water vapor needed to saturate a kilogram of air at
various temperatures, the saturation mixing ratio.
Temperature
(°C) (°F)
Water vapor content at
saturation (g/kg)
-40 -40 0.1
-30 -22 0.3
-20 -4 0.75
-10 14 2
0 32 3.5
5 41 5
10 50 7
15 59 10
20 68 14
25 77 20
30 86 26.5
35 95 35
40 104 47
10. To illustrate the relation between the amount of water vapor needed for
saturation and temperature, prepare a graph in Excel of water vapor content at
saturation and temperature (°C). Label axes and include a title. Submit the graph
with your completed lab. [3 pt]
11. Using Table 1 and/or your graph from question 10, write a statement that
relates the amount of water vapor needed for saturation to temperature. How does
water vapor change as you change the temperature? [2 pt]
12. Using Table 1 data and/or the graph from question 10, what is the water vapor
content at saturation of a kilogram of air at each of the following temperatures?
[4 pt]
-5°C: ____________________________________
12°C: ____________________________________
21°C: ____________________________________
34°C: ____________________________________
13. Using Table 1 data and/or the graph from question 10, what is the air
temperature (°C) at each of the following saturated water vapor contents?
[4 pt]
0.3 g/kg: ____________________________________
8 g/kg: ____________________________________
17 k/kg: ____________________________________
35 g/kg: ____________________________________
14. From Table 1, raising the air temperature of a kilogram of air 10°C, from 15°C to25°C, (increases, decreases) the amount of water vapor for saturation (10, 20)
grams. However, raising the temperature from 25°C to 35°C (increases, decreases)
the amount by (5, 15) grams. [4 pt]
SECTION 5.3 – MEASURING HUMIDITY
15. Use Table 1 and the formula for relative humidity to determine the relative
humidity for each of the following situations with identical temperatures. [3 pt]
Air Temperature Water Vapor Content Relative Humidity
30°C 5 g/kg
30°C 10 g/kg
30°C 20 g/kg
16. From question 15, if the temperature remains constant, adding water vapor will
(raise, lower) the relative humidity, while removing water vapor will (raise, lower)
the relative humidity. [2 pt]
17. Use Table 1 and the formula for relative humidity to determine the relative
humidity for each of the following situations of identical water vapor content. [3 pt]
Air Temperature Water Vapor Content Relative Humidity
25°C 0.75 g/kg
15°C 0.75 g/kg
5°C 0.75 g/kg
18. From question 17, if the amount of water vapor in the air remains constant,
cooling will (raise, lower) the relative humidity, while warming will (raise, lower) the
relative humidity. [2 pt]
19. In the winter, air is heated in homes in colder climates. What effect does heating
have on relative humidity inside the home? What is a possible solution to lessen this
effect? [2 pt]
20. Explain why the air in a cool basement is humid (damp) in the summer. [2 pt]
21. What are two ways that the relative humidity of the air can be changed? [2 pt]
One of the misconceptions concerning relative humidity is that it alone gives an
accurate indication of the actual quantity of water vapor in the air. For example, on a
winter day if you hear on the radio that the relative humidity is 90%, can you
conclude that the air contains more water vapor than on a summer day that records
a 40% relative humidity? Completing question 21 will help you find the answer.
22. Use Table 1 to determine the water vapor content for each of the following
situations. As you do the calculations, keep in mind the definition of relative
humidity. [2 pt]
Summer Winter
Temperature (°C) 25 -20
Relative Humidity (%) 75 75
Content (g/kg)
23. Explain why relative humidity does not give an accurate indication of the actual
amount of water vapor in the air. [1 pt]
SECTION 5.4 – DEW–POINT TEMPERATURE
24. By referring to Table 1, what is the dew-point temperature of a kilogram of air
that contains 2 grams of water vapor? [1 pt]
Dew-point temperature = _______________°C
25. What is the relative humidity and dew-point temperature of a kilogram of air at
20°C that contains 3.5 grams of water vapor? [2 pt]
Relative Humidity = _______________%
Dew-point temperature = _______________°C
26. If the air parcel in question 25 retains its water vapor content and decreases to
10°C, what is the new relative humidity and dew-point temperature? [2 pt]
Relative Humidity = _______________%
Dew-point temperature = _______________°C
27. Is the air parcel in question 26 approaching saturation? Explain. [2 pt]
28. Use Table 2 to determine the relative humidity for each of the following
psychrometer readings. [4 pt]
Reading 1 Reading 2
Dry-bulb temperature (°C) 14 32
Wet-bulb temperature (°C) 11 18
Wet-bulb depression (°C)
Relative humidity (%)
29. From question 28, what is the relation between the difference in the dry-bulb
and wet-bulb temperatures (wet-bulb depression) and the relative humidity of the
air? [2 pt]
30. Which reading is closer to saturation? Why? [2 pt]
31. Use Table 3 to determine the dew-point temperature of each of the following
psychrometer readings. [4 pt]
Reading 1 Reading 2
Dry-bulb temperature (°C) 30 30
Wet-bulb temperature (°C) 15 20
Wet-bulb depression (°C)
Dew-point temperature (°C)
32. Which reading was likely taken in a dry air environment? Why? [2 pt]
33. Digital Psychrometer Exercise
Students will break up into groups of 3-4. Using the digital psychrometer, record a
dry-bulb and wet-bulb temperature inside the building and outside the building.
When looking at the face of the psychrometer, the dry-bulb temperature is on the
left and the wet-bulb temperature is on the right. Place your readings in the blanks
provided in table below and proceed to complete the remainder of the table using
Tables 2 and 3. [10 pt]
Inside Outside
Dry-bulb temperature (°C)
Wet-bulb temperature (°C)
Wet-bulb depression (°C)
Dew-point temperature (°C)
Relative humidity (%)
SECTION 5.5 – DAILY TEMPERATURE AND RELATIVE HUMIDITY
Figure 2 shows the typical daily variations in air temperature, relative humidity and
dew-point temperature during two consecutive spring days at a mid-latitude city.
Use the figure to answer questions 34-38.
34. Relative humidity is at its maximum at (6 A.M., 3 P.M.) on Day (1, 2). [2 pt]
35. The lowest temperature over the two-day period occurs at (6 A.M., noon, 3 P.M.)
on Day (1, 2). [2 pt]
36. The lowest relative humidity occurs at (6 A.M., noon, 3 P.M.) on Day (1, 2).
[2 pt]
37. Write a general statement describing the relationship between temperature and
relative humidity throughout the time period shown in this figure. [2 pt]
38. Did a dew or frost form on either of the two days in this figure? If so, list the
time it occurred and explain how you arrived at your answer. [2 pt]
SECTION 5.6 – CONDENSATION
39. How many grams of water vapor will condense on a surface if a kilogram of air
at 86°F with a relative humidity of 100% is cooled to 59°F? Refer to Table 1. [1 pt]
___________ grams of water will condense
40. Assume a kilogram of air at 30°C contains 10 grams of water vapor. Using Table
1, determine how many grams of water vapor will condense out if the air’s
temperature is lowered to each of the following temperatures. [2 pt]
15°C: ____________ grams of condensed water
5°C: ____________ grams of condensed water
41. When condensation occurs, what three (3) conditions must be achieved in the
atmosphere? (Hint: Look in previous sections for the answers) [3 pt]
SECTION 5.7 – THE ADIABATIC PROCESS AND CLOUDS/PRECIPITATION
42. What is the saturation mixing ratio, content and dew-point temperature of the
air at sea level? [3 pt]
Saturation mixing ratio: _____________ g/kg of air
Content: _____________ g/kg of air
Dew-point temperature: _____________°C
43. The air at sea level is (saturated, unsaturated) [1 pt]
44. The air will initially (warm, cool) as it rises over the windward side of the
mountain at the (moist, dry) adiabatic rate, which is (10, 5)°C per 1000 meters.
[3 pt]
45. What will be the air’s temperature at 500 meters? [1 pt]
_____________°C at 500 meters
46. The rising air will reach its dew-point temperature at _______________ meters and water vapor will begin to (condense, evaporate). [2 pt]
47. From the altitude where condensation begins to occur to the summit of the
mountain, the rising air will continue to expand and will (warm, cool) at the (moist,
dry) adiabatic lapse rate of about _____________°C per 1000 meters. [3 pt]
48. The temperature of the rising air at the summit of the mountain will be
_____________°C. [1 pt]
49. Assuming the air begins to descend on the leeward side of the mountain, it will
be compressed and its temperature will (increase, decrease). [1 pt]
50. Assume the relative humidity of the air is below 100% during its entire descent
to the plateau. The air will be (saturated, unsaturated) and will warm at the (wet,
dry) adiabatic rate of about _____________°C per 1000 meters. [3 pt]
51. As the air descends and warms on the leeward side of the mountain, its relative
humidity will (increase, decrease). [1 pt]
52. The air’s temperature when it reaches the plateau at 2,000 will be
_____________°C. [1 pt]
53. Explain why mountains might cause wet conditions on their windward side and
dry conditions on their leeward sides (i.e. adiabatically). Describe the land type you
might find on each side of the mountain barrier. [4 pt]
SECTION 5.8 – GLOBAL AND REGIONAL PATTERNS OF PRECIPITATION
Use Figure 4 to answer questions 54-57 and Figure 5 to answer questions
58-60
54. Analyzing Figure 4, where are the highest and lowest global average annual
precipitation measurements? Give the geographical region in the space below. [2 pt]
Highestmeasurement:__________________________________________________
Lowest measurement: __________________________________________________
55. In general, the polar regions of the Earth have (high, low) average annual
precipitation. [1 pt]
56. According to Figure 4, (continents, oceans) experience more precipitation
annually? Explain your reasoning. [2 pt]
57. It is possible to distinguish different land types using precipitation
measurements. Given the color scale in Figure 4, where would you expect deserts
and rainforests to be present? Give specific locations. [2 pt]
58. Analyzing Figure 5, where is the highest and lowest average annual precipitation
measurements in the U.S.? Name each state. [2 pt]
Highest measurement:__________________________________________________
Lowest measurement: __________________________________________________
59. With U.S. geography in mind, the highest precipitation falls (along the coast, in
the interior of the country). Explain your reasoning. [2 pt]
60. Describe the general pattern (west to east) of annual precipitation across the
United States. What is the major reason for the aridity of the dry areas in the U.S.?
[3 pt]
