Operator`s manual

61
Manual
ES = c
w
x
w
S (D
i
T
i2
– D
i
T
i1
)
in which:
ES = change in energy storage [J]
cw = the specific heat of water [J C-
1
g-
1
]
w = the mass density of water [g M
-3
]
Di = height of depth layer i
T
i1
= average temperature of depth layer i at time step 1
T
i2
= average temperature of depth layer i at time step 2
BOX 3: Calculation of net long-wave radiation for a water body of 20 °C, in an arid region with a surrounding
average air temperature of 20 °C, and an average relative humidity of 35%.
e
sat
= 0.611 exp( 17.3 T
a
/ (T
a
+ 237.3))
e
sat
= 2.34 [kPa]
e
d
= RH x e
sat
= 0.35 * 2.34 = 0.819 [kPa]
in which RH is relative humidity [%]
’ = 0.34 – 0.14 √e
d
= 0.34 – 0.14 √0.585 = 0.213
f = adjustment for cloud cover = 1 (arid region with predominant clear skies)
This leads to:
R
net-long-wave
= -f ’ (T + 273.2)
4
= -1 x 0.213 x 4.903 x 10
-3
x (20 + 273.3)
4
R
net-long-wave
= - 7.73 x 10
6
[J M-
2
day-
1
]
This equals an average daily outgoing radiation of 7.73 x 10
6
/ 86400 = 89 [J M
-2
s
-1
] = 89 [W M
-2
]
Annexes