Calculating turbulent transport tensors by averaging single plume
  dynamics and application to dynamos
  Transport coefficients in turbulence are comprised of correlation functions
between turbulent fluctuations and efficient methods to calculate them are
desirable. For example, in mean field dynamo theories used to model the growth
of large scale magnetic fields of stars and galaxies, the turbulent
electromotive force is commonly approximated by a series of tensor products of
turbulent transport coefficients with successively higher order spatial
derivatives of the mean magnetic field. One ingredient of standard models is
the kinematic coefficient of the zeroth order term, namely the averaged kinetic
pseudotensor $\bm{\alpha}$, that converts toroidal to poloidal fields. Here we
demonstrate an efficient way to calculate this quantity for rotating stratified
turbulence, whereby the pre-averaged quantity is calculated for the motion of a
single plume, and the average is then taken over an ensemble of plumes of
different orientations. We calculate the plume dynamics in the most convenient
frame, before transforming back to the lab frame and averaging. Our concise
configuration space calculation gives essentially identical results to previous
lengthier approaches. The present application exemplifies what is a broadly
applicable method.
