Geoscience Reference
In-Depth Information
temperature is sinusoidal, and if he chooses the form of the sinusoidal wave to agree
with the timing and magnitude of the minimum and maximum soil temperatures
that he measured and also selects values of soil properties appropriate for the moist
sandy soil, he can calculate the soil heat flux at any time during the day.
(a) What were the values of the mean soil surface temperature, and the
amplitude and the time slip of the cycle in soil surface temperature that he
selected?
(b) What were the values of soil thermal conductivity,
k
s
, and thermal
diffusivity,
α
s
, that he selected, what was the value of damping depth,
D
, for
the daily time period (expressed in seconds) that he calculated. Which
equation from
Terrestrial Hydrometeorology
did he use to calculate the
instantaneous surface soil heat flux?
The farmer assumes that the psychrometric constant is 0.0667 kPa K
−1
when
applying the wet-bulb equation and when calculating the Bowen ratio. For
simplicity he also assumes that the difference in virtual potential temperature is
equal to the difference in measured air temperature between the two levels. (This
is a common assumption when calculating Bowen ratio). In the course of his
calculations he found that the all-day average air temperature and vapor pressure
at the bottom level were the same as those you calculated and used in question
2(a). Using these values with the day of the year and latitude of the site he was able
to calculate the same estimates of net radiation for this arid site that you calculated
in question 2(d). You can therefore adopt those values of hourly net radiation for
use in this question.
(c) Develop a spreadsheet to tabulate the values of vapor pressure at the bot-
tom level, vapor pressure at the top level, Bowen ratio, net radiation [copied
from 2(e)], soil heat flux, available energy, latent heat flux and sensible heat
flux at hourly intervals between 0.5 and 23.5 hours.
(d) Plot the calculated net radiation, soil heat flux, available energy, latent heat
flux and sensible heat flux as a function of time through the day.
(e) What were the all-day average values of the Bowen ratio and Evaporative
Fraction at his site on this day?
(f ) Suppose the farmer had chosen to neglect soil heat flux in his calculation of
available energy. Without recalculating all the rates, can you suggest
whether he would have overestimated or underestimated the all-day
average evaporative fraction and explain why?
Question 4
(Uses understanding from Chapters 1, 2, and 8.)
(a) Shuttleworth says, 'As an annual-average, the value is about 1.2 m. However
we, as land dwellers, see only about 10% of this, and we lose almost two-
thirds back to the atmosphere. We keep an even smaller proportion
