  We use local Cartesian simulations with a vertical gravitational potential to
study how supernova (SN) feedback in stratified galactic discs drives
turbulence and launches galactic winds. Our analysis includes three disc models
with gas surface densities ranging from Milky Way-like galaxies to gas-rich
ultra-luminous infrared galaxies (ULIRGs), and two different SN driving schemes
(random and correlated with local gas density). In order to isolate the physics
of SN feedback, we do not include additional feedback processes. We find that,
in these local box calculations, SN feedback excites relatively low
mass-weighted gas turbulent velocity dispersions ~3-7 km/s and low wind mass
loading factors < 1 in all the cases we study. The low turbulent velocities and
wind mass loading factors predicted by our local box calculations are
significantly below those suggested by observations of gas-rich and rapidly
star-forming galaxies; they are also in tension with global simulations of disc
galaxies regulated by stellar feedback. Using a combination of numerical tests
and analytic arguments, we argue that local Cartesian boxes cannot predict the
properties of galactic winds because they do not capture the correct global
geometry and gravitational potential of galaxies. The wind mass loading factors
are in fact not well-defined in local simulations because they decline
significantly with increasing box height. More physically realistic
calculations (e.g., including a global galactic potential and disc rotation)
will likely be needed to fully understand disc turbulence and galactic
outflows, even for the idealized case of feedback by SNe alone.
