Читать книгу Exploring the Solar System - Peter Bond - Страница 44

Between the radiative zone and the outer convective zone is a relatively thin transition region, known as the interface layer, or tachocline. There, the stable conditions of the radiative zone gradually disappear, to be replaced by the more turbulent fluid motions found in the convection zone.

Although it is extremely difficult to investigate conditions at such depth within the Sun, recent investigations indicate that the Sun's magnetic field is generated by a dynamo effect in this layer. Shear flows – changes in fluid flow velocities across the layer – stretch and increase the strength of magnetic field lines of force. Observations reveal that the speed of plasma in layers above and below the supposed dynamo region can change by 20% in six months. Furthermore, when the lower gas speeds up, the upper gas slows down, and vice versa.

There also seem to be sudden changes in chemical composition across the tachocline. Variations in temperature and pressure, originating in the tachocline and spreading into the convection zone through the transport of heat, may also be the key to differences in the rate of rotation of the Sun's surface.