Abstract
Full disk vector magnetic fields are used widely for developing better understanding of large-scale structure, morphology, and patterns of the solar magnetic field. The data are also important for modeling various solar phenomena. However, observations of vector magnetic fields have one important limitation that may affect the determination of the true magnetic field orientation. This limitation stems from our ability to interpret the differing character of the Zeeman polarization signals which arise from the photospheric line-of-sight vs. the transverse components of the solar vector magnetic field, and is likely exacerbated by unresolved structure (non-unity fill fraction) as well as the disambiguation of the 180° degeneracy in the transverse-field azimuth. Here we provide a description of this phenomenon, and discuss issues, which require additional investigation.
Highlights
Observations of magnetic fields provide key information for developing our understanding of the Sun’s short-term and long-term activity and in predicting these effects on Earth
This limitation stems from our ability to interpret the differing character of the Zeeman polarization signals which arise from the photospheric line-of-sight vs. the transverse components of the solar vector magnetic field, and is likely exacerbated by unresolved structure as well as the disambiguation of the 180° degeneracy in the transverse-field azimuth
Beginning in 2010, full disk vector magnetograms are available from the Helioseismic and Magnetic Imager (HMI, Scherrer et al, 2012) on board the Solar Dynamics Observatory (SDO)
Summary
Observations of magnetic fields provide key information for developing our understanding of the Sun’s short-term (space weather) and long-term (space climate) activity and in predicting these effects on Earth. By the early 1980s, a number of vector magnetographs were developed around the world, with the most prolific instruments operating in Czechoslovakia, East Germany (Pflug & Grigoryev, 1986), Japan (NAOJ, Ichimoto et al, 1993), the Soviet Union (Crimean, Pulkovo and Sayan observatories), and the USA (NASA’s Marshall Space Flight Center/ MSFC, Mees Solar Observatory of University of Hawaii, High Altitude Observatory/HAO) (for review, see individual articles in Hagyard, 1985; Cacciani et al, 1990) All of these instruments had a limited field of view, typically about the size of an average active region.
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