Abstract
We briefly review the history of observations of magnetic fields on the Sun, and describe early magnetograps for full disk measurements. Changes in instruments and detectors, the cohort of observers, the knowledge base etc may result in non-uniformity of the long-term synoptic datasets. Still, such data are critical for detecting and understanding the long-term trends in solar activity. We demonstrate the value of historical data using studies of active region tilt (Joy’s law) and the evolution of polar field and its reversal. Using the longest dataset of sunspot field strength measurements from Mount Wilson Observatory (1917-present) supplemented by shorter datasets from Pulkovo (1956–1997) and Crimean (1956-present) observatories we demonstrate that the magnetic properties of sunspots did not change over the last hundred years. We also show that the relationship between the sunspot area and its magnetic flux can be used to extend the studies of magnetic field in sunspots to periods with no direct magnetic field measurements. Finally, we show how more recent full disk observations of the vector magnetic field can be used to study the long-term (solar cycle) variations in magnetic helicity on the Sun.
Highlights
The Sun is our nearest star, and its activity largely determines the complex processes which collectively are called “space weather” and “space climate”
We summarize the results of a number of studies employing long-term synoptic datasets including the evolution of the polar magnetic fields (Sect. 8), polarity and tilt orientation of active regions (Sect. 9), the use of sunspot areas as a proxy for the magnetic flux in sunspots (Sect. 10), and the studies of helicity on the Sun
Past studies have found that the fraction of active regions, which deviate from the rule are usually smaller than 10% of all active regions: 1.4–6.3% (Hale et al, 1919, MWO sunspot 1913–1917 dataset),
Summary
The Sun is our nearest star, and its activity largely determines the complex processes which collectively are called “space weather” and “space climate”. One of the most important ingredients of solar activity is the magnetic field. The magnetic field helps to channel energy through the solar atmosphere. It stores the energy, which is later released in the course of violent eruptive event, flares and coronal mass ejections (CMEs). The magnetic field defines important features such as sunspots, chromospheric filaments, and coronal holes. As a humorous saying attributed to the late Robert (Bob) Leighton, a prominent American astronomer, puts it: “If the sun didn’t have a magnetic field, it would be as boring a star as most astronomers think it is.”. We start from describing the early history of the magnetic field observations on the Sun We follow up with the description of the synoptic observations of sunspot field strengths (Sect. 3)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
