Geoscience Reference
In-Depth Information
Answer 2
(a) At this site on this day, the all-day average air temperature is 22°C, or
295.13 K, the saturated vapor pressure is 2.644 kPa, and the vapor pressure
is 1.322 kPa.
(b) When calculating net longwave radiation, the effective emissivity
e
'
= 0.194
[from Equation (5.23)] and assuming
c
= 0.7 all through the day, for an arid
site the empirical
cloud factor f
= 0.37 [from Equation (5..25)]. The esti-
mated all-day average net longwave radiation is therefore -28 W m
−2
[from
Equation (5..22)].
(c) Were this a humid site the empirical cloud factor,
f
, would then be 0.533
[from Equation (5..24)] and the estimated all-day average net longwave
radiation would be -41 W m
−2
[from Equation (5..22)].
(d) July 12 is Day Of Year 193, hence the eccentricity factor
d
l
= 0.968 [from
Equation (5.5)] and the solar declination
= 0.385 radians [from Equation
(5.8)]. The latitude of the site is 32.5°N, which is +0.567 radians, and the
hour angle,
w
, can be calculated in radians from the time of day,
t
, in hours
[using Equation (5.10)], with
t
running in hourly increments from 0.5 to
23.5. Consequently, the solar radiation at the top of the atmosphere,
S
top
, can
be calculated [from Equation (26.1)] and solar radiation at the ground,
S
grnd
,
calculated [from Equation (26.2)]. Values of net solar radiation can then
be calculated for each value of
t
by allowing for the albedo of 0.23 [by
comparison with Equation (5.18)]. Values of net radiation can then be cal-
culated for each value of
t
by adding the relevant values of longwave radiation
for arid and humid conditions calculated in sections (b) and (c), respectively.
The resulting values of solar radiation, net solar radiation, and net radiation
for an arid and a humid site are given in Table 26.5 and plotted in Fig. 26.5.
(e) The required all-day average values are 190 W m
−2
for (incoming) solar
radiation, 146 W m
−2
for net solar radiation, 118 W m
−2
for net radiation at
this arid site, and 105 W m
−2
for net radiation were it assumed to be a
humid site.
(f ) The required all-day average fluxes and plots of the diurnal variation in
solar, net solar, and net radiation for the Saskatoon site with fresh snow
cover on January 15 and grassland cover on July 15 are given in Fig. 26.6.
(g) The required all-day average fluxes and plots of the diurnal variation in
solar, net solar, and net radiation for the Manaus site on March 23 with for-
est and pastureland cover given in Fig. 26.7.
δ
Answer 3
(a) The mean soil surface temperature,
T
m
, is (24+20)/2 = 22°C, the amplitude
of the daily cycle,
T
a
, is (24-20)/2 = 2°C, and the time slip,
t
o
, which gives a
minimum 01.00 am and a maximum at 13.00 in Equation (6.11) is (7 ×
60 × 60) = 25,200 seconds.
