Le séminaire a lieu le jeudi
5 avril 2001 de 14h30 à 15h30
dans la salle de réunion
du PHC (Observatoire de Nice).
Alpha quenched alpha-squared, omega
dynamo waves in stellar shells
Andrew M. Soward, University
of Exeter (UK)
Nonlinear alpha-squared, omega-dynamo waves are considered
in a thin turbulent, differentially rotating convective
stellar shell. Nonlinearity arises from alpha-quenching,
while an asymptotic solution is based on the small aspect
ratio of the shell. Wave modulation is linked to a
latitudinal-dependent local alpha-effect and zonal shear
flow
magnetic Reynolds numbers. Finite amplitude dynamo waves
are
modulated by an envelope which evaporates smoothly at
some
low latitude but is terminated abruptly by a front at
a high
latitude. For sufficiently large alpha-effect magnetic
Reynolds numbers, a steady polar cap solution also exists.
Then the waves ride up on top of it and are again terminated
by a front. Front location and wave frequency are predicted
analytically and are compared favourably with the full
integration of the governing amplitude equations.