The onset of thermal convection in a rotating spherical shell of intermediate radius ratio ¼ 0:4 is
studied numerically for Taylor numbers Ta 1011 and the Prandtl number of the liquid sodium ( ¼
0:01). For the first time, it is shown that at very high Taylor numbers the first unstable mode can be
antisymmetric with respect to the equator and confined inside a cylinder tangent to the inner sphere at the
equator (polar mode). The exponent of the power law determined from the asymptotic dependence of the
critical Rayleigh number for very high Ta is 0.57, lower than 2=3, given theoretically for the spiraling
columnar modes, and than 0.63, found numerically for the outer equatorially attached modes
CitacióGarcia, F.; Net, M.; Sánchez, J. Antisymmetric polar modes of thermal convection in rotating spherical fluid shells at high Taylor numbers. "Physical Review Letters", 03 Novembre 2008, vol. 101, núm. 19, p. 194501-1-194501-4.