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https://stockholmuniversity.zoom.us/j/940229961
We investigate the effect of the surface tilted bipolar magnetic regions (BMR) on the large-scale dynamo distributed in the bulk of the convection zone. The study employs the nonlinear 3D mean-field dynamo model. The emergence of the BMR on the surface is modeled by means of the nonaxisymmetric magnetic buoyancy effect which acts on the large-scale toroidal magnetic field in the upper half of the convection zone. The nonaxisymmetric magnetic field which results from this mechanism is shallow. At the surface the effect of the BMR on the magnetic field generation is dominant. However, because of the shallow BMR distribution, its effect on the global dynamo is moderate. The most dynamo effect of the surface BMR is due to their evolution and the convective zone α effect. The fluctuations of the BMR's tilt affect the equatorial symmetry of the dynamo-generated magnetic field. In agreement with the solar observations, the emerging BMRs result in the negative magnetic helicity density of the large-scale nonaxisymmetric magnetic fields in the northern hemisphere of the star.