Title: Helioseismology challenges models of solar convection Authors: Laurent Gizon, Aaron C. Birch
Convection is the mechanism by which energy is transported through the outermost 30% of the Sun. Solar turbulent convection is notoriously difficult to model across the entire convection zone where the density spans many orders of magnitude. In this issue of PNAS, Hanasoge et al. (2012) employ recent helioseismic observations to derive stringent empirical constraints on the amplitude of large-scale convective velocities in the solar interior. They report an upper limit that is far smaller than predicted by a popular hydrodynamic numerical simulation.
A new study by UCLA planetary scientists and their colleagues in Germany overturns a longstanding scientific tenet and provides new insights into how convection controls much of what we observe in planets and stars. The research, federally funded by the National Science Foundation, unifies results from an extensive array of previous experiments. It appears in the Jan. 15 edition of the journal Nature.
"The Nature paper allows us new and meaningful predictions for where we should observe different behaviours throughout the universe wherever there are rotating convection systems, and that means planets and stars. This allows us to make predictions for almost any body where we can measure the rotation rate and heat coming out. For me, that's exciting" - Study co-author Jonathan Aurnou, a UCLA associate professor of planetary physics.
Convection describes the transfer of heat, or thermal energy, from one location to another through the movement of fluids such as liquids, gases and slow-flowing solids. As an example, when a bowl of water is heated on a stove, the heated portion of the water becomes buoyant and rises through the surrounding cooler water, while the cooler water drops down to be heated, creating a convection current.