Geoscience Reference
In-Depth Information
Air temperature (°C)
-60
-50
-40
-30
-20
-10
9.164
400
7.185
500
5.574
600
4.206
700
3.012
W.B. Potential temp. (°K)
Sat. adiabats
800
1.949
900
988
1000
1050
111
-302
1.0
2
4
8
16
Saturation mixing ratio (g kg-1)
Figure 5.1
Adiabatic charts like the tephigram allow the following properties of the atmosphere to be
displayed: temperature, pressure, potential temperature, wet-bulb potential temperature and saturation
(humidity) mixing ratio.
1000
0.286
P
650
=
T
{-
---
}
p
θ
w
2
T
1
θ
2
Height
pressure
X
s
1
X
s
2
θ
1
θ
w
1
where
and
T
are in K, and
p
= pressure (mb).
The relationship between
T
and
P
850
; also between
T
2
T
and
w
, the wet-bulb potential temperature
(where the air parcel is brought to a pressure of
1000mb by a saturated adiabatic process), is
shown schematically in
Figure 5.2
. Potential
temperature provides an important yardstick for
air mass characteristics, since if the air is affected
only by dry adiabatic processes the potential
temperature remains constant. This helps to
P
1000
T
d
T
w
T
A
Temperature
Saturation mixing ratio
Figure 5.2
Graph showing the relationships between
temperature (T), potential temperature (
θ
), wet-bulb potential
temperature (
θ
w
) and saturation mixing ratio (x
s
). T
d
= dew-
point, T
w
= wet-bulb temperature and T
A
= air temperature.
