scholarly journals Long-term studies of photospheric magnetic fields on the Sun

2020 ◽  
Author(s):  
Alexei Pevtsov ◽  
Luca Bertello ◽  
Yuri Nagovitsyn ◽  
Andrey Tlatov ◽  
Valery Pipin
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Measurements ◽  
Sunspot Area ◽  
The Sun ◽  
Mount Wilson Observatory ◽  
History Of ◽  
Long Term Trends ◽  
Full Disk

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.

scholarly journals On the manifestation in the Sun-as-a-star magnetic field measurements of the quiet and active regions

2010 ◽  
Vol 6 (S273) ◽  
pp. 56-60 ◽  
Author(s):  
Mikhail Demidov
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Active Regions ◽  
Field Measurements ◽  
Solar Observatory ◽  
Spectral Lines ◽  
The Sun ◽  
Time Data ◽  
Full Disk

AbstractThe best way to test the stellar magnetic field mapping codes is to apply them, with some changes, to the Sun, where high-precision disk-integrated and disk-resolved observations are available for a long time. Data sets of the full-disk magnetograms and the solar mean magnetic fields (SMMF) measurements are provided, for example, by the J.M.Wilcox Solar observatory (WSO) and by the Sayan Solar observatory (SSO). In the second case the measurements in the Stokes-meter mode simultaneously in many spectral lines are available. This study is devoted to analysis of the SSO quasi-simultaneous full-disk magnetograms and SMMF measurements. Changes of the SMMF signal with rotation of the surface large-scale magnetic fields are demonstrated. Besides, by deleting of selected pixels with active regions (AR) from the maps their contribution to the integrated SMMF signal is evaluated. It is shown that in some cases the role of AR can be rather significant.

scholarly journals Reconstructing solar magnetic fields from historical observations

2019 ◽  
Vol 628 ◽  
pp. A103 ◽  
Author(s):  
Alexei A. Pevtsov ◽  
Kseniya A. Tlatova ◽  
Alexander A. Pevtsov ◽  
Elina Heikkinen ◽  
Ilpo Virtanen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Solar Magnetic Field ◽  
Field Measurements ◽  
Solar Magnetic Fields ◽  
Mount Wilson Observatory ◽  
Magnetic Field Measurements ◽  
History Of ◽  
Selection Of

Context. Systematic observations of magnetic field strength and polarity in sunspots began at Mount Wilson Observatory (MWO), USA in early 1917. Except for a few brief interruptions, this historical dataset has continued until the present. Aims. Sunspot field strength and polarity observations are critical in our project of reconstructing the solar magnetic field over the last hundred years. We provide a detailed description of the newly digitized dataset of drawings of sunspot magnetic field observations. Methods. The digitization of MWO drawings is based on a software package that we developed. It includes a semiautomatic selection of solar limbs and other features of the drawing, and a manual entry of the time of observations, measured field strength, and other notes handwritten on each drawing. The data are preserved in an MySQL database. Results. We provide a brief history of the project and describe the results from digitizing this historical dataset. We also provide a summary of the final dataset and describe its known limitations. Finally, we compare the sunspot magnetic field measurements with those from other instruments, and demonstrate that, if needed, the dataset could be continued using modern observations such as, for example, the Vector Stokes Magnetograph on the Synoptic Optical Long-term Investigations of the Sun platform.

scholarly journals Solar Full-Disk Polarization Measurement with the Fe I 15648 Å Line

2014 ◽  
Vol 10 (S305) ◽  
pp. 92-96
Author(s):  
Y. Hanaoka ◽  
T. Sakurai ◽  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Near Infrared ◽  
Active Regions ◽  
Zeeman Splitting ◽  
Polarization Measurement ◽  
The Sun ◽  
Horizontal Field ◽  
The Magnetic Field ◽  
Full Disk

AbstractThe near-infrared absorption line Fe I 15648 Å, which has a Landé g-factor of 3, shows a particularly large Zeeman splitting. We regularly take full-disk polarization maps of the Sun in the Fe I 15648 Å line (as well as the He I 10830 Å line) with an infrared spectropolarimeter installed at the Solar Flare Telescope of the National Astronomical Observatory of Japan (NAOJ). It is known that weak, mostly horizontal magnetic fields are ubiquitously distributed in the quiet regions of the Sun, while the strong magnetic fields are concentrated in active regions and network boundaries. The weak horizontal field has not been sufficiently investigated due to the difficulty of such observations. The polarization maps in Fe I 15648 Å show the magnetic field strength at each pixel, regardless of the filling factor, so we can easily isolate the weak horizontal field signals from strong magnetic field ones using the Stokes V profiles of the Fe I 15648 Å line. Here we present instrumental aspects and observational results of solar near-infrared full-disk polarimetry. We highlight the weak horizontal field inferred from Fe I 15648 Å.

scholarly journals Long-Term Coherent Periodicities in the Mean Magnetic Field of the Sun

1983 ◽  
Vol 102 ◽  
pp. 23-27
Author(s):  
V.A. Kotov ◽  
L.S. Levitsky
Keyword(s):  
Magnetic Field ◽  
Mean Field ◽  
Field Measurements ◽  
Magnetic Star ◽  
Time Interval ◽  
The Sun ◽  
Total N ◽  
The Mean ◽  
Made In

To investigate periodic variations of the magnetic field of the Sun as a star (SMMF; see Severny, 1969) we have used the mean field measurements made in Crimea, Mt. Wilson, and Stanford observatories; in total N = 5783 daily values were available for the time interval 1968–1981. In essence, these data offer a unique possibility to study the Sun as a variable magnetic star (Scherrer et al., 1977).

Emergence of Twisted Magnetic Flux Related Sigmoidal Brightening

2000 ◽  
Vol 179 ◽  
pp. 263-264
Author(s):  
K. Sundara Raman ◽  
K. B. Ramesh ◽  
R. Selvendran ◽  
P. S. M. Aleem ◽  
K. M. Hiremath
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Ultra Violet ◽  
Active Regions ◽  
Morphological Properties ◽  
Energy Storage And Conversion ◽  
The Sun ◽  
X Rays ◽  
The Magnetic Field

Extended AbstractWe have examined the morphological properties of a sigmoid associated with an SXR (soft X-ray) flare. The sigmoid is cospatial with the EUV (extreme ultra violet) images and in the optical part lies along an S-shaped Hαfilament. The photoheliogram shows flux emergence within an existingδtype sunspot which has caused the rotation of the umbrae giving rise to the sigmoidal brightening.It is now widely accepted that flares derive their energy from the magnetic fields of the active regions and coronal levels are considered to be the flare sites. But still a satisfactory understanding of the flare processes has not been achieved because of the difficulties encountered to predict and estimate the probability of flare eruptions. The convection flows and vortices below the photosphere transport and concentrate magnetic field, which subsequently appear as active regions in the photosphere (Rust & Kumar 1994 and the references therein). Successive emergence of magnetic flux, twist the field, creating flare productive magnetic shear and has been studied by many authors (Sundara Ramanet al.1998 and the references therein). Hence, it is considered that the flare is powered by the energy stored in the twisted magnetic flux tubes (Kurokawa 1996 and the references therein). Rust & Kumar (1996) named the S-shaped bright coronal loops that appear in soft X-rays as ‘Sigmoids’ and concluded that this S-shaped distortion is due to the twist developed in the magnetic field lines. These transient sigmoidal features tell a great deal about unstable coronal magnetic fields, as these regions are more likely to be eruptive (Canfieldet al.1999). As the magnetic fields of the active regions are deep rooted in the Sun, the twist developed in the subphotospheric flux tube penetrates the photosphere and extends in to the corona. Thus, it is essentially favourable for the subphotospheric twist to unwind the twist and transmit it through the photosphere to the corona. Therefore, it becomes essential to make complete observational descriptions of a flare from the magnetic field changes that are taking place in different atmospheric levels of the Sun, to pin down the energy storage and conversion process that trigger the flare phenomena.

“Theoretically all Children are Equal. Practically this can Never be So”: The History of the District Property Tax in California and the Choice of Inequality

2020 ◽  
Vol 122 (2) ◽  
pp. 1-32
Author(s):  
Matthew Gardner Kelly
Keyword(s):  
School Finance ◽  
Research Question ◽  
Property Tax ◽  
School Funding ◽  
State Governments ◽  
Property Taxation ◽  
History Of ◽  
Long Term Trends ◽  
Funding Disparities

Background/Context Dealing mostly in aggregate statistics that mask important regional variations, scholars often assume that district property taxation and the resource disparities this approach to school funding creates are deeply rooted in the history of American education. Purpose/Objective/Research Question/Focus of Study This article explores the history of district property taxation and school funding disparities in California during the 19th and 20th centuries. First, the article documents the limited use of district property taxation for school funding in California and several other Western states during the 19th century, showing that the development of school finance was more complicated than standard accounts suggest. Then, the article examines how a coalition of experts, activists, and politicians worked together during the early 20th century to promote district property taxation and institutionalize the idea that the wealth of local communities, rather than the wealth of the entire state, should determine the resources available for public schooling. Research Design This article draws on primary source documents from state and regional archives, including district-level funding data from nine Northern California counties, to complete a historical analysis. Conclusions/Recommendations The history of California's district property tax suggests the need for continued research on long-term trends in school finance and educational inequality. Popular accounts minimizing the historical role of state governments in school funding obscure how public policies, not just market forces shaping property values, create funding inequalities. In turn, these accounts communicate powerful messages about the supposed inevitability of funding disparities and the responsibility of state governments to correct them. Through increased attention to long-term trends in school funding, scholars can help popular commentators and policymakers avoid assumptions that naturalize inequality and narrow the possibilities for future funding reforms.

scholarly journals Implementation of a Faraday rotation diagnostic at the OMEGA laser facility

2018 ◽  
Vol 6 ◽  
Author(s):  
A. Rigby ◽  
J. Katz ◽  
A. F. A. Bott ◽  
T. G. White ◽  
P. Tzeferacos ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Faraday Rotation ◽  
Field Measurements ◽  
Thomson Scattering ◽  
Proton Radiography ◽  
Time Resolved ◽  
Rotation Measurement ◽  
Laser Facility ◽  
Omega Laser

Magnetic field measurements in turbulent plasmas are often difficult to perform. Here we show that for ${\geqslant}$kG magnetic fields, a time-resolved Faraday rotation measurement can be made at the OMEGA laser facility. This diagnostic has been implemented using the Thomson scattering probe beam and the resultant path-integrated magnetic field has been compared with that of proton radiography. Accurate measurement of magnetic fields is essential for satisfying the scientific goals of many current laser–plasma experiments.

scholarly journals Repeat station data compared to a global geomagnetic field model

2013 ◽  
Vol 55 (6) ◽  
Author(s):  
Monika Korte ◽  
Vincent Lesur
Keyword(s):  
Magnetic Field ◽  
Secular Variation ◽  
Global Model ◽  
Time Interval ◽  
Night Time ◽  
Core Field ◽  
Repeat Station ◽  
Station Data ◽  
Long Term Trends

<p>Geomagnetic repeat station surveys with local variometers for improved data reductions have been carried out in Germany for about ten years. For nearly the same time interval the satellites Ørsted and CHAMP have provided a good magnetic field data coverage of the whole globe. Recent global field models based on these satellite data together with geomagnetic observatory data provide an improved description of the core field and secular variation. We use the latest version of the GFZ Reference Internal Magnetic Model to compare the magnetic field evolution predicted by that model between 2001 and 2010 to the independent repeat station data collected over the same time interval in Germany. Estimates of crustal bias at the repeat station locations are obtained as averages of the residuals, and the scatter or trend around each average provides information about influences in the data from field sources not (fully) described by the global model. We find that external magnetic field signal in the order of several nT, including long-term trends, remains both in processed annual mean and quiet night time repeat station data. We conclude that the geomagnetic core field secular variation in this area is described to high accuracy (better than 1 nT/yr) by the global model. Weak long-term trends in the residuals between repeat station data and the model might indicate induced lithospheric anomalies, but more data are necessary for a robust analysis of such signals characterized by very unfavorable signal-to-noise ratio.</p>

11. The United Kingdom: Towards a Parting of the Ways

2020 ◽  
pp. 257-279
Author(s):  
Anand Menon ◽  
Luigi Scazzieri
Keyword(s):  
European Union ◽  
Public Opinion ◽  
Institutional Development ◽  
The European Union ◽  
Integration Process ◽  
The United Kingdom ◽  
History Of ◽  
Long Term Trends ◽  
The Uk

This chapter examines the history of the United Kingdom’s relationship with the European integration process. The chapter dissects the long-term trends in public opinion and the more contingent, short-term factors that led to the referendum vote to leave the European Union. The UK was a late joiner and therefore unable to shape the early institutional development of the EEC. British political parties and public opinion were always ambiguous about membership and increasingly Eurosceptic from the early 1990s. Yet the UK had a significant impact on the EU’s development, in the development of the single market programme and eastward enlargement. If Brexit goes through, Britain will nevertheless maintain relations with the EU in all policy areas from agriculture to energy and foreign policy. Europeanization will remain a useful theoretical tool to analyse EU–UK relations even if the UK leaves the Union.

Sign in / Sign up

Export Citation Format

Share Document