We study the influence of a dynamo magnetic field on the buoyant rise and emergence of twisted magnetic flux-ropes , and their influence on the global external magnetic field .
We ran three-dimensional MHD numerical simulations using the ASH code and analysed the dynamical evolution of such buoyant flux-ropes from the bottom of the convection zone until the post-emergence phases .
The global nature of this model can only very crudely and inaccurately represent the local dynamics of the buoyant rise of the implanted magnetic structure , but allows nonetheless to study the influence of global effects such as self-consistently generated differential rotation and meridional circulation , and the influence of the Coriolis forces .
Although motivated by the solar context , this model can not be thought of as a realistic model of the rise of magnetic structures and their emergence in the Sun where the local dynamics are completely different .
The properties of initial phases of the buoyant rise are determined essentially by the flux-rope ’ s properties and the convective flows and are , in consequence , in good agreement with previous studies .
However , the effects of the interaction of the background dynamo field become increasingly stronger as the flux-ropes evolve .
During the buoyant rise across the convection zone , the flux-rope ’ s magnetic field strength and scales as B \propto \rho ^ { \alpha } , with \alpha \lesssim 1 .
An increase of radial velocity , density and current density is observed to precede flux emergence at all longitudes .
The geometry , latitude and relative orientation of the flux-ropes with respect to the background magnetic field influences the resulting rise speeds , zonal flows amplitudes ( which develop within the flux-ropes ) and the corresponding surface signatures .
This influences the morphology , duration and amplitude of the surface shearing and the Poynting flux associated with magnetic flux-rope emergence .
The emerged magnetic flux influences the system ’ s global polarity , leading in some cases to a polarity reversal while inhibiting background dynamo from doing so in some others .
The emerged magnetic flux is slowly advected poleward , while being diffused and assimilated by the background dynamo field .