Geography Reference
In-Depth Information
Fig. 3.7
Trajectories for moving circular cyclonic
circulation systems in the Northern
Hemisphere with (a) V
=
2C and (b)
2V
=
C. Numbers indicate positions
at successive times. The L designates a
pressure minimum.
slope of the isobaric surfaces with respect to the
x
axis also must increase with
height as shown in Fig. 3.8. According to the hypsometric Eq. (1.21), the thickness
δz corresponding to a pressure interval δp is
g
−
1
RT δ ln p
δz
≈−
(3.25)
Thus, the thickness of the layer between two isobaric surfaces is proportional
to the temperature in the layer. In Fig. 3.8 the mean temperature T
1
of the column
denoted by δz
1
must be less than the mean temperature T
2
for the column denoted
by δz
2
. Hence, an increase with height of a positive
x
directed pressure gradient
must be associated with a positive
x
directed temperature gradient. The air in a
vertical column at x
2
, because it is warmer (less dense), must occupy a greater
depth for a given pressure drop than the air at x
1
.
