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SUMMARY:Magnetic flux emergence and solar dynamo models - Laurène Jouve
DTSTART:20090526T120000Z
DTEND:20090526T130000Z
UID:TALK18146@talks.cam.ac.uk
CONTACT:Dr. Aurélien Crida
DESCRIPTION:We present the first 3D MHD study in spherical geometry of the
  non-linear dynamical evolution of magnetic flux tubes in a turbulent rota
 ting convection zone. These numerical simulations use the anelastic spheri
 cal harmonic (ASH) code. We seek to understand the mechanism of emergence 
 of strong toroidal fields through a turbulent layer from the base of the s
 olar convection zone to the surface as active regions\, with a particular 
 focus on the effects of self-consistently generated mean flows.\n\nWeak fi
 eld cases indicate that downflows and upflows control the rising velocity 
 of particular regions of the rope and could in principle favour the emerge
 nce of flux through Ω-loop structures. For these cases\, we focus on the 
 orientation of bipolar regions and find that sufficiently arched structure
 s are able to create bipolar regions with a predominantly East-West orient
 ation. Meridional circulation seems to determine the trajectory of the mag
 netic rope when the field strength has been significantly reduced near the
  top of the domain. Local field emergence also feeds back on the horizonta
 l flows thus perturbing the meridional circulation via Maxwell stresses. F
 inally differential rotation makes it more difficult for tubes introduced 
 at low latitudes to emerge at the surface.\n\nWe reintroduce these 3D resu
 lts in 2D mean-field Babcock-Leighton flux-transport dynamo models\, and i
 n particular the time-delay caused by the emergence of toroidal structures
  from the base of the CZ to the surface. We find that these time delays in
 troduce a strong modulation of the solar cycle amplitude\, even when stron
 g and thus rapidly rising flux tubes are considered. This modulated activi
 ty and the resulting butterfly diagram are then more compatible with obser
 vations than the standard Babcock-Leighton model.
LOCATION:MR14\, DAMTP\, Pav. F
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