Agronomy 405/505
Spring 2009
Problem Set 3
Due Tuesday, February 3, 2009
Assigned January 27, 2009
1. (a) What is the dew point temperature if the ambient temperature is 20◦ C and the
relative humidity is 0.60?
(b) If the dew point temperature is 15◦ C, what is the ambient water vapor pressure?
At what ambient temperature will the relative humidity be 0.40?
2. 3.5 in Campbell and Norman.
3. In this problem, you will compare how relative humidity, dew point temperature, ambient water vapor pressure, and water vapor concentration vary with time. Use the
MATLAB data file aR8x.mat in the tar file on the web site for Class #2.
(a) Plot ambient air temperature (measured at 7.8 m) versus time beginning on day
of year 191 (July 10) and continuing through the end of day of year 194 (four
days). Use the m–file r8x_temps.m that I used to create the PDF in Class #2
as a guide. This data was collected over a 100 acre maize crop in southeastern
Michigan. On July 13 the crop was 2.2 m high.
(b) Plot relative humidity (also measured at 7.8 m) versus time for the same time
period in another figure.
(c) Compute, then plot water vapor pressure and saturation water vapor pressure
versus time in a new figure for the same time period. Suggestion: create a MATLAB function using (3.8) in Campbell and Norman, or use my function sat_vp.m
on the course website. My function uses the following empirical expression:
h
es = 101.325 exp α tR − β tR 2 − γ tR 3 − δ tR 4
i
(1)
where tR = 1 − 373.15/T with T in kelvin, α = 13.3185, β = 1.9760, γ = 0.6445,
and δ = 0.1299.
(d) Compute, then plot water vapor concentration in terms of mole fraction versus
time in another figure for the same time period. Use the expression for pressure
given in Campbell and Norman and an elevation of 200 m above sea level.
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(e) Compute, then plot water vapor concentration in terms of mass concentration
versus time in another figure for the same time period.
(f) Compute, then plot dew point temperature and air temperature versus time in
another figure for the same time period. Use (3.14) in Campbell and Norman.
(g) Compare and contrast how relative humidity, water vapor pressure, water vapor
concentration (in terms of both mole fraction and mass concentration), and dew
point temperature vary with time.
i.
ii.
iii.
iv.
Which variables have a significant diurnal variation?
At what time during the diurnal cycle is each quantity maximum?
At what time during the diurnal cycle is each quantity minimum?
What likely occured the morning of day of year 191?
A plot is required for each part 3a – 3f. I encourage you to use the sub–plot command
in order to put several plots on the same figure. Please also include your m–file.
4. 3.6 in Campbell and Norman.
5. 4.3 in Campbell and Norman.
6. 4.4 in Campbell and Norman.
7. 4.5 in Campbell and Norman.
8. 4.6 in Campbell and Norman.
9. Read “Severe Heat and Cold Top List of Deadly Natural Hazards” from Science News
at http://snipurl.com/8u1gf.
(a) What are the top two most dangerous natural hazards in terms of human deaths?
(b) What type of natural hazard are we most likely to have in Iowa?
(c) Why haven’t the fatalities from Hurricane Katrina been included in this study?
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