The Solar Cycle Variation of Topological Structures in the Global Solar Corona

Abstract

The distribution of magnetic flux across the solar photosphere results in a complex web of coronal magnetic field structures. To understand this complexity, the magnetic skeleton of the coronal field can be calculated. The skeleton highlights the separatrix surfaces that divide the field into topologically distinct regions, allowing open-field regions on the solar surface to be located. Furthermore, separatrix surfaces and their intersections (separators) are important likely energy release sites. This paper investigates, throughout the solar cycle, the nature of coronal magnetic-field topologies that arise under the potential-field source-surface approximation. In particular, we characterise the typical global fields at solar maximum and minimum. Global magnetic fields are extrapolated from observed Kitt Peak and SOLIS synoptic magnetograms, from Carrington rotations 1645 to 2144, using the potential-field source-surface model. Hence, variations in the coronal skeleton are studied over three solar cycles. Key building blocks which make up magnetic fields are identified and classified according to the nature of their separatrix surfaces. The magnetic skeleton reveals that, at solar maximum, the global coronal field involves a multitude of topological structures at all latitudes. Many open-field regions exist originating anywhere on the photosphere. At solar minimum, the coronal topology is heavily influenced by the solar dipole. A strong dipole results in a simple large-scale structure involving just two large polar open-field regions, but, at short radial distances between plus or minus 60 deg latitude, the small-scale topology is complex. If the solar dipole if weak, as in the recent minimum, then the low-latitude quiet-sun magnetic fields may be globally significant enough to create many disconnected open-field regions at low latitudes, in addition to the two polar open-field regions.

References in corpus (5)

• A trilinear method for finding null points in a 3D vector space
• Structure and Dynamics of the Sun's Open Magnetic Field
• Computing nonlinear force-free fields in spherical geometry
• The Number Of Magnetic Null Points In The Quiet Sun Corona
• The Solar Cycle Variation of Topological Structures in the Global Solar Corona

Cited by in corpus (10)

• The Magnetic Field in the Solar Atmosphere
• The Solar Cycle Variation of Topological Structures in the Global Solar Corona
• The effect of reconnection on the structure of the Sun's open-closed-flux boundary
• Three-Year Global Survey of Coronal Null Points from Potential-Field-Source-Surface (PFSS) Modeling and Solar Dynamics Observatory (SDO) Observations
• Magnetic reconnections in the presence of three-dimensional magnetic nulls and quasi-separatrix layers
• Is Magnetic Topology Important for Heating the Solar Atmosphere?
• The Minimal Helicity of Solar Coronal Magnetic Fields
• On the importance of separators as sites of 3D magnetic reconnection
• Coronal Dynamic Activities in the Declining Phase of a Solar Cycle
• Topology of Coronal Magnetic Fields: Extending the Magnetic Skeleton Using Null-like Points