## Lamb dipole crossing a ridge -- with background rotation

*Details on the computation and presentation*

**Initialisation**
Dipole: velocity: U = 2; maximum initial vorticity 44.25
radius: a = 0.5
angle of dipole axis with X-axis: 0 degrees
position: centre of the domain (-1.5,0)
Computation: domain: X = (-3, ..., 3), Y = (-3, ..., 3)
no. of grid points from wall to wall: (129, 129)
boundary conditions: stress-free along all walls
standard Arakawa scheme used
viscosity: nu = 10^-3 (i.e. Re=1000 at T=0)
time step: dt = 0.01
final time: T = 2.5
Background rotation: constant rotation f0 = 4, 6 and 8
Bottom topography: cosine ridge along the Y-axis:
fluid depth: H(X,Y) = 1.d0-A*cos(X*pi/w)-A
amplitude: A = 0.2 (max. height then 0.4)
width: w = 1.0
for: -w < x < +w
outside this region: H=1 (default fluid depth)
Tracers: along vorticity contours (i.e. along streamlines)
of the Lamb dipole at vorticity levels: 0.1
and a single tracers at each extremum

**Some results**
Here are the graphs for the maximum (left) and minimum (right)
vorticity as a function of time for the three rotation rates:

The positive half of the dipole is more or less restored for
all three values of f0. The negative half is restored for
f0=4 and 8 but torn apart for f=8.

<=== Lamb dipole crossing a ridge -- with
background rotation

**
Jos van Geffen** --
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###### created: 11 July 1997

last modified: 26 May 2001