Investigating the Polar Flux Budget with the Advective Flux Transport Model

The strength of the magnetic field at the Sun’s poles near the time of a sunspot cycle minimum is a crucial component to the solar dynamo and is thought to determine the strength of the following solar activity cycle. Unfortunately, our knowledge of the polar magnetic field is limited to what can be gleaned from measurements taken from the ecliptic on the Sun-Earth line; a vantage point from which the dynamics of polar field evolution are not easily observable. Many surface flux transport models use a loss term, thought to represent the subduction of magnetic flux to the interior, in order to accurately reproduce the evolution of the polar fields. Others include the emergence of ephemeral active regions in the polar regions. We use the realistic Advective Flux Transport (AFT) model, in combination with HMI observations, to simulate the evolution of the Sun’s polar magnetic fields for three different scenarios: pure flux transport, flux transport with subduction, and flux transport with ephemeral emergence. We show the impact of these different scenarios on the polar flux budget and discuss the advantages that a polar viewpoint, like that of the SOLARIS mission, will provide for measuring and understanding polar magnetic field evolution.