Abstract
In this review, our present day understanding of the Sun's global photospheric and coronal magnetic fields is discussed from both observational and theoretical viewpoints. Firstly, the large-scale properties of photospheric magnetic fields are described, along with recent advances in photospheric magnetic flux transport models. Following this, the wide variety of theoretical models used to simulate global coronal magnetic fields are described. From this, the combined application of both magnetic flux transport simulations and coronal modeling techniques to describe the phenomena of coronal holes, the Sun's open magnetic flux and the hemispheric pattern of solar filaments is discussed. Finally, recent advances in non-eruptive global MHD models are described. While the review focuses mainly on solar magnetic fields, recent advances in measuring and modeling stellar magnetic fields are described where appropriate. In the final section key areas of future research are identified.
Highlights
Magnetic fields play a key role in the existence and variability of a wide variety of phenomena on the Sun
We primarily focus on our present day understanding of global solar magnetic fields from both observations and theoretical models
The standard equation of magnetic flux transport arises from the radial component of the magnetic induction equation under the assumptions that vr = 0 and ∂/∂r = 0.1 These assumptions constrain the radial field component to evolve on a spherical shell of fixed radius, where the time evolution of the radial field component is decoupled from the horizontal field components
Summary
Global Coronal Models (Section 3) This section of the review surveys the wide variety of techniques used to model global coronal magnetic fields This includes the various approximations that are applied from static extrapolation techniques, to time dependent quasi-static models and recent advances in global non-eruptive MHD models. Application of Global Models (Section 4) The final part of the review considers the combined application of both magnetic flux transport models and coronal modeling techniques to model a variety of phenomena found on the Sun. These include the Sun’s open magnetic flux (Section 4.1), coronal holes (Section 4.2), and the hemispheric pattern of solar filaments (Section 4.3).
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