Helical impurity distribution produced by a hydrodynamic instability

Temperature oscillations have been recorded in the liquidn phase during vertical solidarification of salt solutions and dilute aqueous suspensions. The oscillations produce a characteristic solidification pattern consisting of a helical segragation of impurities. The pitch of the helix is correlated with the temperature period of the oscillation. A model is proposed based on unstable thermal convection. It involves the rotation of a convective roll around its own axis. It is shown that the solidification technique provides a new method for the determination of the characteristics of the convective behaviour.