Turbulent Thermal Convection - Selected Topics of Computational and Experimental Fluid Mechanics - page 37

On the Earth's surface, convection plays a fundamental role in weather and
climate, driving the oceans (Marshall and Schott 1999 ) as well as the atmosphere
(Hartmann et al. 2001 ). In the Earth's interior, convection plays a role both in the
outer core (Cardin and Olson 1994 ) and in the mantle (Schubert et al. 2001 ). The
convective liquid metal flows in the core are thought to be responsible of the Earth's
magnetic field through a dynamo mechanism (Buffett 2000 ). The convective mantle
motion is related to the phenomenon of plate tectonics (Tackley 2000 ); even when
planets do not show plate tectonics, as in the case of Venus or Mars, mantle con-
vection is important because of its role in transporting heat from the planet interior
to the surface. In giant planets, which have a hot interior, convection occurs when
conduction and radiation are not sufficient to transport all the heat (Guillot 2005 ).
In the Sun, the nuclear energy generated at the core is transported by the convective
motion in the outer 30 % of the radius. This motion shows cellular structures on
different scales, distinguished usually as granular (2,000 km), mesoscale (5,000-
10,000 km), supergranular (3 10 5 km) cells (Nordlund

et al. 2009 ). Cellular structures driven by convective motions are also evident in the
atmosphere (see Fig. 1 ).
Many basic questions relating to these diverse systems are similar. How do we
predict the heat transfer due to the convective motion? Conversely, what flow structure
is needed to transport a given amount of thermal energy? How important are the
macroscopic large scale structures? What is their dynamics? What are the properties
of the small scale turbulence? How does the small scale motion relate to large scales?
And so forth.

10 4 km) and giant (1-2 × ×

Fig. 1 Cellular convective structures in natural phenomena. a Sun's granular structure where each
cell is on the order of 1,000 km. Image from Swedish 1-m Solar Telescope (SST)—Royal Swedish
Academy of Sciences—Oddbjorn Engvold, Jun Elin Wiik, Luc Rouppe van der Voort. b Closed
cells structures in a layer of marine stratocumulus over the southeastern Pacific Ocean. Each cell is
on the order of 5 km. Image by NASA/GSFC/LaRC/JPL, MISR Team