Plumes in stellar convection zones

All numerical simulations of compressible convection reveal the presence of strong downwards directed flows. Thanks to helioseismology, such plumes have now been detected also at the top of the solar convection zone, on supergranular scales. Their properties may be crudely described by adopting Taylor’s turbulent entrainment hypothesis, whose validity is well established under various conditions. Using this model, one finds that the strong density stratification does not prevent the plumes from traversing the whole convection zone, and that they carry upwards a net energy flux. They penetrate to some extent in the adjacent stable region, where they establish an almost adiabatic stratification when there is little radiative diffusion. These plumes have a strong impact on the dynamics of stellar convection zones, and they play probably a key role in the dynamo mechanism. Proceedings of the Fourteenth International Annual Florida Workshop in Nonlinear Astronomy and Physics, “Astrophysical Turbulence and Convection” , University of Florida, Feb. 1999 (to appear in the Annals of the New York Academy of Sciences)