Variations in the solar luminosity, radius, and quadrupole moment as effects of a large-scale dynamo in the solar convection zone

Abstract

The effect of large-scale magnetic fields generated by the solar dynamo on the irradiance of the Sun and stratification of the solar convection zone is studied using a numerical model of a spherical axisymmetric dynamo. This model provides a joint description of the generation of large-scale magnetic fields, differential rotation, and convective heat transfer taking into account energy transformations associated with the large-scale magnetic fields, as well as the stratification of the convection zone. The model further develops a previously suggested self-consistent approach to analyzing solar luminosity variations, based on the conservation of the energy of the large-scale magnetic fields and turbulent flows. The results indicate that the increase in the solar luminosity near the maximum of the cycle is mainly due to the dissipation of the energy of magnetic fields escaping to above the photosphere, with the partial conversion of this energy into radiation. In addition, near-photospheric magnetic fields strongly affect the latitudinal nonuniformity of the cyclic variations in the radiative flux. The large-scale magnetic field also influences the hydrostatic equilibrium of the convection zone and gives rise to 11-year variations in the sound speed with a relative amplitude of 10−3. The cyclic magnetic activity generates oscillations in the quadrupole moment with an amplitude of 4.5 × 10−9(GM⊙/R⊙). According to our estimates, the variations in the solar radius are very small, ∼10−6R⊙. Our numerical model is used to estimate the variations in the orbital periods of close binaries whose primaries have the same spectral class as the Sun. Modulation of the centrifugal force by torsional oscillations can provide a plausible explanation for variations in the orbital periods of the companion stars in these systems.