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3.6 The base of the convection zone

Inversions to determine the radial profile of sound speed and other structure quantities have been used to great effect in improving our understanding of the physics which goes into solar structure models (e.g., Gough, 1996Jump To The Next Citation PointChristensen-Dalsgaard, 2002Jump To The Next Citation Point). In the context of solar interior dynamics, the most important contribution of structure inversions has been to locate the base of the solar convection zone at rb = 0.713 ± 0.003Ro . (Christensen-Dalsgaard et al., 1991), defined as the radius at which the stratification changes from nearly adiabatic stratification to substantially sub-adiabatic stratification (see Section 8.1). This result has until recently been viewed as very reliable but new elemental abundance determinations have called it into question (Asplund et al., 2005Bahcall et al., 2005). Helioseismic estimates further suggest that the extent of the overshoot region below the convection zone is no more than about 5% of a pressure scale height, which is less than 1% of the solar radius (Monteiro et al., 1994Jump To The Next Citation PointBasu, 1997Jump To The Next Citation Point). Basu and Antia (2001) find no significant variations in either rb or the thickness of the overshoot region with latitude or time (variations in the structure of the tachocline obtained from rotational inversions are discussed in Sections 3.2 and 3.3).
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