Geoscience Reference
In-Depth Information
Geostrophic wind
Consider Equations (16.36) and (16.37) which describe momentum conservation
in the X and Y directions when applied to atmospheric flow
above
the atmospheric
boundary layer. In this case the atmosphere is assumed to be in a steady state and
consequently the time differentials on the left hand side of Equations (16.36) and
(16.37) are zero. Also in this case, terms describing molecular diffusion can be
neglected in comparison with other terms in the equations, i.e., in these equations:
du
dv
(17.11)
=
0;
=
0;
u
∇
2
u
=
0;
u
∇
2
v
=
0
dt
dt
Equations (16.36) and (16.37) can therefore be re-written as:
1
∂
∂
P
(17.12)
U
=−
g
f
r
y
a
1
∂
∂
P
(17.13)
V
=
g
f
r
x
a
where
f
angular velocity of the Earth.
The wind speed components
U
g
and
V
g
are components of the
Geostrophic Wind
which is generated by the large-scale pressure gradients, see Fig. 17.1. Thus, mean
atmospheric flow above the ABL is parallel to the isobars, with low pressure on the
left in the northern hemisphere and low pressure on the right in the southern
hemisphere.
=
2
ω
sin(
θ
), with
q
is the latitude and
ω
Y
P
P
+
Δ
P
Low
P
+ 2
Δ
P
G
V
g
U
g
Figure 17.1
Axial components of the geostrophic wind
in the northern hemisphere in a region with pressure
gradients.
High
X
