  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 > 1.5x10^4 G and the twist >
5.0x10^-4 km^-1 at -20,000 km depth.
