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The Origin of the Sun’s Dynamo and the extended 22-Years Solar Cycle

A study published late September depicts the mean rotation rate of the Sun as a function of velocity vs. radius at different latitudes. The subsurface boundary shear and the angular velocity gradient gives rise to a latitudinal migration of a toroidal field dynamic with a cycle of 22 Years, and the magnetic field as a primary driver of torsional oscillations on the surface.

All manifestations of solar activity, from spectral irradiance variations to solar storms and geomagnetic disturbances, are caused by the magnetic fields generated by a dynamo mechanism operating in the convection zone deep below the visible surface of the Sun.
Despite substantial modeling and simulation efforts, our understanding of how the magnetic field is generated, transported to the surface and forms the solar activity cycles is very poor.

Torsional oscillations were discovered from the analysis of velocity distribution on the solar surface, utilizing Helioseismology data from 1996-2018 obtained from SoHO and SDO, as well as MDI and HMI. As the study shows the zonal velocity signal is extended beneath the solar surface and the entire solar convective envelope appears to be involved in torsional oscillation with phase propagating poleward and equatorward from mid latitudes at all depths throughout the convective envelope. The magnetic active emerge on the boundary between the fast and slow zones, which originate at high latitudes and migrate towards the equator as the solar cycle progresses.

The Wave-like patterns of zonal deceleration are related to the magnetic field evolution during the solar cycles in the convection zone. Close association of the deceleration zones with magnetic field indicates that the magnetic field is a primary driver of the torsional oscillations.

RSF View: Parker’s Dynamo Theory (1955) describes the action of convection in a rotating frame upon a toroidal magnetic field line and its twisting due to Coriolis force. The Haramein-Rauscher solution to Einstein’s field equations describes where this force originates from (The Origin of Spin, 2005).

The zonal acceleration diagram also shows prominent zones of acceleration suggesting that inertial forces and other factors affecting redistribution of the angular momentum play an important role.

The latitudinal migration of the toroidal field in the form of the butterfly diagram is due to a horizontal gradient of angular velocity and radial rotational shear in the subsurface layer.

Because the observed zonal flow pattern is long-living and coherent over essentially the whole solar circumference it cannot be of convective origin, but can be associated with dynamo, and inertial waves. The whole flow cycle takes 22 years, which is as twice as long the sunspot cycle.

Although the relationship between the magnitude of zonal deceleration and the amount of emerged toroidal field that leads to formation of sunspots is not yet established this opens a new perspective for solar cycle prediction.

Authors: Alexander G. Kosovichev and Valery V. Pipin
Picture of Titel: “The Current State of Solar Modeling”, in Science, volume 272, 1996, Bibcode1996Sci...272.1286C, pages 1286

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