  Aims. We study the emergence of a non-twisted flux tube from the solar
interior into the solar atmosphere. We investigate whether the length of the
buoyant part of the flux tube (i.e. {\lambda}) affects the emergence of the
field and the dynamics of the evolving magnetic flux system. Methods. We
perform three-dimensional (3D), time-dependent, resistive, compressible MHD
simulations using the Lare3D code. Results. We find that there are considerable
differences in the dynamics of the emergence of a magnetic flux tube when
{\lambda} is varied. In the solar interior, for larger values of {\lambda}, the
rising magnetic field emerges faster and expands more due to its lower magnetic
tension. As a result, its field strength decreases and its emergence above the
photosphere occurs later than in the smaller {\lambda} case. However, in both
cases, the emerging field at the photosphere becomes unstable in two places,
forming two magnetic bipoles that interact dynamically during the evolution of
the system. Most of the dynamic phenomena occur at the current layer, which is
formed at the interface between the interacting bipoles. We find the formation
and ejection of plasmoids, the onset of successive jets from the interface, and
the impulsive heating of the plasma in the solar atmosphere. We discuss the
triggering mechanism of the jets and the atmospheric response to the emergence
of magnetic flux in the two cases.
