Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005an....326...61k&link_type=abstract
Astronomische Nachrichten, Vol.326, Issue 1, p.61-74
Astronomy and Astrophysics
Astronomy
8
Sun, Sun: Α Ω Dynamo, Sun: Sunspots
Scientific paper
In order to extend the abilities of the α Ω dynamo model to explain the observed regularities and anomalies of the solar magnetic activity, the negative buoyancy phenomenon and the magnetic quenching of the α effect were included in the model, as well as newest helioseismically determined inner rotation of the Sun were used. Magnetic buoyancy constrains the magnitude of toroidal field produced by the Ω effect near the bottom of the solar convection zone (SCZ). Therefore, we examined two "antibuoyancy" effects: i)~macroscopic turbulent diamagnetism and ii)~magnetic advection caused by vertical inhomogeneity of fluid density in the SCZ, which we call the \nablaρ effect. The Sun's rotation substantially modifies the \nablaρ effect. The reconstruction of the toroidal field was examined assuming the balance between mean-field magnetic buoyancy, turbulent diamagnetism and the rotationally modified \nablaρ effect. It is shown that at high latitudes antibuoyancy effects block the magnetic fields in the deep layers of the SCZ, and so the most likely these deep-rooted fields could not become apparent at the surface as sunspots. In the near-equatorial region, however, the upward \nablaρ effect can facilitate magnetic fields of about 3000 -- 4000 G to emerge through the surface at the sunspot belt. Allowance for the radial inhomogeneity of turbulent velocity in derivations of the helicity parameter resulted in a change of sign of the α effect from positive to negative in the northern hemisphere near the bottom of the SCZ. The change of sign is very important for direction of the Parker's dynamo-waves propagation and for parity of excited magnetic fields. The period of the dynamo-wave calculated with allowance for the magnetic quenching is about seven years, that agrees by order of magnitude with the observed mean duration of the sunspot cycles. Using the modern helioseismology data to define dynamo-parameters, we conclude that north-south asymmetry should exist in the meridional field. At low latitudes in deep layers of the SCZ, the α Ω dynamo excites most efficiency the dipolar mode of the meridional field. Meanwhile, in high-latitude regions a quadrupolar mode dominates in the meridional field. The obtained configuration of the net meridional field is likely to explain the magnetic anomaly of polar fields (the apparent magnetic "monopole") observed near the maxima of solar cycles.
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