438
DANIELSEN
NORTH
SOUTH
NORTH
SOUTH
FRo
Nigc}
On,&
NORTH
SOUTH
NORTH
SOUTH
Fig. 1—Schematic illustrations of tropopause folding and tropospheric
frontogenesis. Lower right diagram is erroneous conventional analysis
of lower left diagram. Thin lines represent potential temperature.
energy, the potential vorticity can be derived, Its exact and approximate mathematical forms are, respectively,
P=aVe- (Vx V + 2)
and
00
Py “~8 op (fq + f)
where P = potential vorticity
a@ = specific volume
V = wind velocity
Q = angular velocity of earth
© = potential temperature
p = pressure
g = acceleration of gravity
Eg =K-VxXV,
f=K- 22
K = unit vector in vertical
Excluding vertically oriented © surfaces, the approximate form is
sufficiently accurate for our purposes and more readily evaluated. In