1
Hydrostatic Balance
•
In the absence of atmospheric motions the gravity force
must be exactly balanced by the vertical component of
the pressure gradient force.
•
Because vertical accelerations are very small for large-
scale atmospheric motions, this is an excellent
approximation for the vertical dependence of pressure in
the real atmosphere.
g
dz
dp
ρ
−
=
∫
∞
=
−
=
−
=
z
dz
g
z
p
dz
g
dp
g
dz
dp
ρ
ρ
ρ
)
(
Pressure at any point is the weight per square meter
of the atmospheric column overlying that point.
kPa
dz
g
p
325
.
101
)
0
(
0
=
=
∫
∞
ρ
For average conditions,
This is the mean sea-level pressure.

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