  We present a numerical study of turbulence and dynamo action in stratified
shearing boxes with zero mean magnetic flux. We assume that the fluid obeys the
perfect gas law and has finite (constant) thermal diffusivity. The calculations
begin from an isothermal state spanning three scale heights above and below the
mid-plane. After a long transient the layers settle to a stationary state in
which thermal losses out of the boundaries are balanced by dissipative heating.
We identify two regimes. A conductive regime in which the heat is transported
mostly by conduction and the density decreases with height. In the limit of
large thermal diffusivity this regime resembles the more familiar isothermal
case. Another, the convective regime, observed at smaller values of the thermal
diffusivity, in which the layer becomes unstable to overturning motions, the
heat is carried mostly by advection and the density becomes nearly constant
throughout the layer. In this latter constant-density regime we observe
evidence for large-scale dynamo action leading to a substantial increase in
transport efficiency relative to the conductive cases.

High Energy Astrophysical Phenomena;Solar and Stellar Astrophysics