Вісник Астрономічної школи (Dec 2018)
Convective overshoot and tachochlin are the most favorable the deep layers of the Sun to excite a toroidal magnetic field
Abstract
The novelty of the models of the turbulent dynamo of the solar cycle, which were proposed in recent years, is that the generation of the poloidal and toroidal components of the global magnetic field does not occur equally effectively in the entire solar convective zone (SCZ), as was previously thought; but this generation is concentrating in distributed areas of the SCZ. In this connection, the question of the localization of the Ω-effect, which excites the toroidal field, becomes a matter of urgency, since the amplitude of the solar cycle depends on the magnitude of the latter one. In this work, the role of deep layers near the bottom of the SCZ, covering the layer of permeable convection (convective overshoot layer) and the tachocline layer, in the generation of a powerful toroidal field is analyzed. The author's recent studies on the role of the deep layers of the SCZ in explaining the observed phenomenon of double peaks of the cycle of sunspots, are noted. In the convective overshoot there are created the necessary conditions for the formation of the layer of prolonged maintenance of magnetic field, whereas in the tachocline due to the sharp decrease in angular velocity in the presence of the weak poloidal field the powerful toroidal field is effectively generated. However, the further evolution of this field occurs in different regimes in the polar and equatorial domains of the SCZ. In the polar domain, two effects of antibuoyancy (macroscopic turbulent diamagnetism and ∇ρ-effect) block magnetic buoyancy of field. Whereas, in the equatorial domain in the lower part of the SCZ, one of the antibuoyancy effects (∇ρ-effect) changes its sign to the opposite, thereby helping Parker's magnetic buoyancy. As a result, the effect of Parker buoyancy is prevailing over the antibuoyancy effect of the macroscopic turbulent diamagnetism. Therefore, after some time, the toroidal field rises to the surface and forms magnetic bipolar groups of sunspots (the first directed upward wave of the toroidal field, which is responsible for the main maximum of the activity of spot formation). An important factor in the processes in the deep layers is the meridional flow directed towards equator, which ensures the migration of the toroidal field near the bottom of the SCZ from the high latitudes to the low ones. Therefore, after 1–2 years the blocked polar toroidal field reaches a site in the equatorial domain, where already there are favorable conditions for its lifting to the surface. Here, this delayed in time toroidal field rises to the solar surface (the second upward magnetic wave) and thus provides the repeating maximum of sunspots.
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