Thursday, 15 January 2004: 2:15 PM
Vortex Trajectories In Atmospheric Flows Represented By Spherical Harmonics
Room 615/616
For point vortex motion on a sphere, the stream function Q is a harmonic
function except for logarithmic singularities at vortex locations.
For n vortices of strengths Ki present at points Pi, the stream function
is given by Q=Q0+sum(Ki*G) where Q0 is stream function of potential flow
independent of Pi and Ki. Spherical harmonics are eigenfunctions for
Laplace-Beltrami operator on a sphere and for study of atmospheric motion on
the planetary scale, superpositional representation by spherical harmonic
components of the stream function is often considered for flow over the sphere.
Spherical harmonic representation of Q0 for point vortex motion on a sphere
enables study of atmospheric vortices and insight into nature and properties of
solutions from differential equations point of view. Integration of forecasting
differential equations using example of cyclones embedded in such an
atmosphere is considered. For low degree and order, the vortical trajectories
are shown to be similar to particle advection by the velocity field of Rossby
waves on barotropic beta-plane.
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