  We numerically demonstrate and characterize the emergence of distinct
dynamical regimes of a finite temperature bosonic superfluid in an elongated
Josephson junction generated by a thin Gaussian barrier over the entire
temperature range where a well-formed condensate can be clearly identified.
Although the dissipation arising from the coupling of the superfluid to the
dynamical thermal cloud increases with increasing temperature as expected, the
importance of this mechanism is found to depend on two physical parameters
associated (i) with the initial chemical potential difference, compared to some
characteristic value, and (ii) the ratio of the thermal energy to the barrier
amplitude. The former determines whether the superfluid Josephson dynamics are
dominated by gradually damped plasma-like oscillations (for relatively small
initial population imbalances), or whether dissipation at early times is
instead dominated by vortex- and sound-induced dissipation (for larger initial
imbalances). The latter defines the effect of the thermal cloud on the
condensate dynamics, with a reversal of roles, i.e. the condensate being driven
by the oscillating thermal cloud, being observed when the thermal particles
acquire enough energy to overcome the barrier. Our findings are within current
experimental reach in ultracold superfluid junctions.
