Time Evolution of Horizontal Subsurface Flows in the Sun

A Mechanism for the Local Production of Faculae

“…For flow over a solid wall half of the overall shear in a turbulent boundary layer occurs across the very thin, high shear layer. Patrón et al (1998) show a similar breakdown for the SPTBL. When the ring bubble gets into this region, the interaction of the ring's vorticity with the high shear layer of the SPTBL results in a local portion of the high shear layer being induced into the Sun by the ring bubble's significantly greater vorticity.…”

“…When the ring bubble gets into this region, the interaction of the ring's vorticity with the high shear layer of the SPTBL results in a local portion of the high shear layer being induced into the Sun by the ring bubble's significantly greater vorticity. We can make a crude estimate of the ratio of strengths of vorticity using the calculated granulation rms vorticity of 0.011 s −1 (Rieutord et al, 2002), and estimating the high shear layer's vorticity from scaling laws and the data of Patrón et al (1998) to be 0.0004 s −1 ; we see that the ring bubble's vorticity is ∼28 times greater than that of the high shear layer. Initially, as the local portion of the high shear layer is induced inward, it is stretched and thus amplified, and its leading edge rolls up into a single discrete hairpin shaped vortex tube, which is unstable to small perturbations, and evolves into multiple hairpin vortices (see Figures 3, 7 and 8).…”

“…Evidence for the presence of a shear flow extending from the photosphere into the Sun approximately 35 Mm, the SPTBL, has been obtained from global helioseismic studies (see Schou et al, 1998Schou et al, , 2002. Local helioseismic studies (see Patrón et al, 1998) have detailed it closer to the photosphere. The global results indicate that a net shear is produced by the slowing down of the rotation of the gases of the Sun as they approach the photosphere.…”

“…Thus, the mean velocity profile of the SPTBL (see Figure 8 of Schou et al, 1998;also Figure 3 of Patrón et al, 1998) can be modeled as essentially two shears with a blending region. A weak shear dominates 85% of the SPTBL, from roughly 35 Mm below the photosphere to five Mm below it.…”

“…The thickness of this high shear layer is usually characterized in units which depend on the knowledge of the shear stress at the boundary (the photosphere), and the local viscosity, for neither of which we have a good measure. Patrón et al (1997Patrón et al ( , 1998 have measured the high shear layer on the Sun using the local helioseismic technique of ring diagram analysis (Hill, 1988). From their figures a rough estimate of its thickness can be made.…”