On the Tachocline Zone Location in the Sun, the Luminosity Transport   time scale, the Rotational Inertia and their Time Variation in Standard Solar   Evolution Models
  Studies with GONG Standard Solar Evolution Models sampling the evolution of the sun from its ZAMS stage show the following. The location of the tachocline zone is nearly fixed as it is not affected by shell burning although it co-moves with the expansion of the sun up to the present age of 4.6 Gyr. The luminosity transport time scale of the sun is entirely dominated by photon diffusion and during the evolution has decreased from over 204000 years to 187000 years. The rotational inertia of the sun shows a small gradual increase from 6.73x10^46 kg m^2 to 7.09x10^46 kg m^2 at present but the inertia constant decreases from 0.0911 to 0.0736 during the same period. 
Mandyam N Anandaram
astro-ph.SR