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*A.J.R. Prentice (Monash University, Victoria, Australia), C.P. Dyt (CSIRO Div. Petroleum Resources, Bentley, Western Australia)*

We report a new set of calculations which support the view
that supersonic turbulent convection played a major role in
the formation of the solar system. A flux-corrected
transport scheme (Zalesak, \textit{J. Comp. Phys.}
\textbf{31} 335 1979) is used to numerically simulate
thermal convection in a 2D ideal gas layer that is heated
from below and is stratified gravitationally across many
scale heights. The temperature T_{0} at the top boundary
and the temperature gradient (\partial T/\partial z)_{1}
at the lower boundary are kept constant during the
computation. The initial atmosphere is superadiabatic with
polytropic index m = 1, specific heats ratio \gamma =
1.4 and temperature contrast T_{1}/T_{0} = 11. This layer
mimics a section of the outer layer of the proto-solar cloud
(Dyt & Prentice, \textit{MNRAS} \textbf{296} 56 1998).
Because the Reynolds number of the real atmosphere is so
large, motions whose scale is less than the computational
grid size

are represented with a Smagorinsky sub-grid scale turbulence
approximation (Chan et al, \textit{Ap.J.} \textbf{263} 935
1982). That is, a velocity-dependent turbulent viscosity
\nu_{t} and thermal diffusivity \kappa_{t}

are chosen so that the high wavenumber kinetic energy spectrum follows Kolmogorov's -5/3 law.

The flow soon evolves to a configuration consisting of a
network of giant convective cells. At cell boundaries, the
downflows are spatially concentrated and rapid. Turbulent
pressures \langle \rho v^{2} \rangle_{t} range up to 3
times the local gas pressure p_{gas}. The convection
eliminates nearly all of the superadiabaticity in the lower
90% of the atmosphere. In the top 10%, \partial
T/\partial z increases sharply and a steep density
inversion occurs, with \rho increasing by a factor of
3-4. This result gives new credibility to the modern
Laplacian theory of solar system origin (\textit{Moon &
Planets} \textbf{19} 341 1978; \textit{ibid} \textbf{73} 237
1996; \textit{Phys. Lett. A} \textbf{213} 253 1996). Even
so, we need \langle \rho v^{2} \rangle_{t} \approx 10
p_{gas} if the proto-solar cloud is to shed discrete gas
rings whose orbits match the mean planetary spacings and
whose chemical condensates

match the observed bulk compositions. This work was funded by the ARC.

The author(s) of this abstract have provided an email address for comments about the abstract: andrew.prentice@sci.monash.edu.au

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