We present the new results of the two-dimensional numerical experiments on the cross-sectional evolution of a twisted magnetic flux tube rising from the deeper solar convection zone ( -20 , 000 { km } ) to the corona through the surface .
The initial depth is ten times deeper than most of previous calculations focusing on the flux emergence from the uppermost convection zone .
We find that the evolution is illustrated by the two-step process described below : the initial tube rises due to its buoyancy , subject to aerodynamic drag due to the external flow .
Because of the azimuthal component of the magnetic field , the tube maintains its coherency and does not deform to become a vortex roll pair .
When the flux tube approaches the photosphere and expands sufficiently , the plasma on the rising tube accumulates to suppress the tube ’ s emergence .
Therefore , the flux decelerates and extends horizontally beneath the surface .
This new finding owes to our large scale simulation calculating simultaneously the dynamics within the interior as well as above the surface .
As the magnetic pressure gradient increases around the surface , magnetic buoyancy instability is triggered locally and , as a result , the flux rises further into the solar corona .
We also find that the deceleration occurs at a higher altitude than in our previous experiment using magnetic flux sheets ( Toriumi and Yokoyama ) .
By conducting parametric studies , we investigate the conditions for the two-step emergence of the rising flux tube : field strength \gtrsim 1.5 \times 10 ^ { 4 } { G } and the twist \gtrsim 5.0 \times 10 ^ { -4 } { km } ^ { -1 } at -20 , 000 { km } depth .