Modeling the Sun’s Large-scale Magnetic Field during the Maunder Minimum

We use a flux transport model to simulate the evolution of the Sun’s magnetic dipole moment, polar fields, and open flux under Maunder minimum conditions. Even when the rate of active region emergence is taken to be a factor of 30 smaller than in recent solar cycles, regular polarity oscillations of the axial dipole and polar fields can be maintained if the speed of the poleward surface flow is reduced from 20 to 10 m s 1 and the source flux emerges at very low latitudes ( 10 ). The axial dipole is then found to have an amplitude of the order of 0.5 G, as compared with 4 G during solar cycle 21. The strength of the radial interplanetary field component at Earth is estimated to be in the range 0.3–0.7 nT, about a factor of 7 lower than contemporary values. We discuss the implications of these weak fields for our understanding of geomagnetic activity and cosmic-ray modulation during theMaunder minimum. Subject headings: interplanetary medium — solar-terrestrial relations — Sun: activity — Sun: corona — Sun: magnetic fields — Sun: photosphere