Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001apj...559..428d&link_type=abstract
The Astrophysical Journal, Volume 559, Issue 1, pp. 428-442.
Astronomy and Astrophysics
Astronomy
134
Magnetohydrodynamics: Mhd, Sun: Magnetic Fields
Scientific paper
We propose an αΩ flux-transport dynamo for the Sun that is driven by a tachocline α-effect. This α-effect comes from the global hydrodynamic instability of latitudinal differential rotation in the tachocline, as calculated using a shallow-water model. Growing, unstable shallow-water modes propagating longitudinally in the tachocline create vortices that correlate with radial motion in the layer to produce a longitude-averaged net kinetic helicity and, hence, an α-effect. We show that such a dynamo is equally successful as a Babcock-Leighton-type flux-transport dynamo in reproducing many large-scale solar cycle features. The success of both dynamo types depends on the inclusion of meridional circulation of a sign and magnitude similar to that seen on the Sun. Both α-effects (the Babcock-Leighton-type and tachocline α-effect) are likely to exist in the Sun, but it is hard to estimate their relative magnitudes. By extending the simulation to a full spherical shell, we show that the flux-transport dynamo driven by the tachocline α-effect selects a toroidal field that is antisymmetric about the equator, while the Babcock-Leighton flux-transport dynamo selects a symmetric toroidal field. Since our present Sun selects antisymmetric fields, we argue that the tachocline α-effect must be more important than the Babcock-Leighton α-effect.
Dikpati Mausumi
Gilman Peter A.
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