MHD simulations of the formation and propagation of protostellar jets to
  observational length scales
  We present 2.5-D global, ideal MHD simulations of magnetically and
rotationally driven protostellar jets from Keplerian accretion discs, wherein
only the initial magnetic field strength at the inner radius of the disc,
$B_{\rm i}$, is varied. Using the AMR-MHD code AZEUS, we self-consistently
follow the jet evolution into the observational regime ($>10^3\,\mathrm{AU}$)
with a spatial dynamic range of $\sim6.5\times10^5$. The simulations reveal a
three-component outflow: 1) A hot, dense, super-fast and highly magnetised 'jet
core'; 2) a cold, rarefied, trans-fast and highly magnetised 'sheath'
surrounding the jet core and extending to a tangential discontinuity; and 3) a
warm, dense, trans-slow and weakly magnetised shocked ambient medium entrained
by the advancing bow shock. The simulations reveal power-law relationships
between $B_{\rm i}$ and the jet advance speed, $v_{\rm jet}$, the average jet
rotation speed, $\langle v_\varphi\rangle$, as well as fluxes of mass,
momentum, and kinetic energy. Quantities that do not depend on $B_{\rm i}$
include the plasma-$\beta$ of the transported material which, in all cases,
seems to asymptote to order unity. Jets are launched by a combination of the
'magnetic tower' and 'bead-on-a-wire' mechanisms, with the former accounting
for most of the jet acceleration---even for strong fields---and continuing well
beyond the fast magnetosonic point. At no time does the leading bow shock leave
the domain and, as such, these simulations generate large-scale jets that
reproduce many of the observed properties of protostellar jets including their
characteristic speeds and transported fluxes.
