Lamb dipole crossing a ridge -- with background rotation

Details on the computation and presentation

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

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created: 11 July 1997
last modified: 26 May 2001