Geography Reference
In-Depth Information
Fig. 10.14
Stationary plane Rossby wave in a westerly flow. Ridges (solid lines) and troughs (dashed
lines) are oriented at an angle α to the y axis, and the group velocity relative to the
ground,
c
g
, is oriented at an angle α to the x axis. The wavelength is 2 π/K
s
. (Adapted
from Hoskins, 1983.)
meridional momentum flux can be expressed as
u
v
=−
∂ψ
∂x
∂ψ
∂y
=−
2
kl
2
From (10.68) it is then verified readily that if u>0,
c
gy
> 0 implies u
v
< 0
c
gy
< 0 implies u
v
> 0
Thus, westerly momentum converges into the wave source region (where the energy
flux is divergent). This eddy momentum flux convergence is necessary to balance
the momentum lost to the surface through the pressure torque mechanism discussed
in Section 10.3.
Fig. 10.15
The vorticity pattern generated on a sphere when a constant angular velocity westerly flow
impinges on a circular forcing centered at 30
◦
N and 45
◦
W of the central point. Left to
right, the response at 2, 4, and 6 days after switch on of the forcing. Five contour intervals
correspond to the maximum vorticity response that would occur in 1 day if there were
no wave propagation. Heavy lines correspond to zero contours. The pattern is drawn on
a projection in which the sphere is viewed from infinity. (After Hoskins, 1983.)
