scholarly journals Magnetohydrostatic modeling of AR11768 based on a SUNRISE/IMaX vector magnetogram

2020 ◽  
Vol 640 ◽  
pp. A103 ◽  
Author(s):  
X. Zhu ◽  
T. Wiegelmann ◽  
S K. Solanki
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Field Measurements ◽  
Plasma Pressure ◽  
Photospheric Magnetic Field ◽  
Solar Photosphere ◽  
Free Layer ◽  
Lower Boundary Condition ◽  
Magnetic Field Measurements ◽  
The Magnetic Field

Context. High-resolution magnetic field measurements are routinely only done in the solar photosphere. Higher layers, such as the chromosphere and corona, can be modeled by extrapolating these photospheric magnetic field vectors upward. In the solar corona, plasma forces can be neglected and the Lorentz force vanishes. This is not the case in the upper photosphere and chromosphere where magnetic and nonmagnetic forces are equally important. One way to deal with this problem is to compute the plasma and magnetic field self-consistently, in lowest order with a magnetohydrostatic (MHS) model. The non-force-free layer is rather thin and MHS models require high-resolution photospheric magnetic field measurements as the lower boundary condition. Aims. We aim to derive the magnetic field, plasma pressure, and density of AR11768 by applying the newly developed extrapolation technique to the SUNRISE/IMaX data embedded in SDO/HMI magnetogram. Methods. We used an optimization method for the MHS modeling. The initial conditions consist of a nonlinear force-free field (NLFFF) and a gravity-stratified atmosphere. During the optimization procedure, the magnetic field, plasma pressure, and density are computed self-consistently. Results. In the non-force-free layer, which is spatially resolved by the new code, Lorentz forces are effectively balanced by the gas pressure gradient force and gravity force. The pressure and density are depleted in strong field regions, which is consistent with observations. Denser plasma, however, is also observed at some parts of the active region edges. In the chromosphere, the fibril-like plasma structures trace the magnetic field nicely. Bright points in SUNRISE/SuFI 3000 Å images are often accompanied by the plasma pressure and electric current concentrations. In addition, the average of angle between MHS field lines and the selected chromospheric fibrils is 11.8°, which is smaller than those computed from the NLFFF model (15.7°) and linear MHS model (20.9°). This indicates that the MHS solution provides a better representation of the magnetic field in the chromosphere.

scholarly journals High Resolution Magnetic Field Measurements in the Sunspot Photosphere

1993 ◽  
Vol 141 ◽  
pp. 11-19
Author(s):  
Axel Hofmann ◽  
Wolfgang Schmidt ◽  
Horst Balthasar ◽  
Theodore T. Tarbell ◽  
Zoe A. Frank
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Field Strength ◽  
Spectral Resolution ◽  
Field Measurements ◽  
Brightness Variation ◽  
Longitudinal Component ◽  
Azimuthal Variation ◽  
Magnetic Field Measurements ◽  
The Magnetic Field

AbstractWe analysed calibrated Stokes V magnetograms and simultaneously measured Stokes I spectra of high spatial and spectral resolution taken in a medium sized sunspot. We found a clear (anti-) correlation between the brightness variation of penumbral structures and the longitudinal component (B*cosγ) of the magnetic field. No azimuthal variation of the amount of the magnetic field strength (B) was observed across dark and bright structures. There the field is more vertical in bright filaments compared to dark ones.

scholarly journals Development of Space Magnetometers in Austria

Proceedings ◽  
2018 ◽  
Vol 2 (13) ◽  
pp. 1104
Author(s):  
Werner Magnes ◽  
Roland Lammegger ◽  
Martin Agú ◽  
Christoph Amtmann ◽  
Özer Aydogar ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar System ◽  
Field Measurements ◽  
Fundamental Information ◽  
Magnetic Field Measurements ◽  
The Magnetic Field

With spaceborne magnetic field measurements it is possible to investigate the interior of planets,moons and asteroids which have either an intrinsic or a crustal magnetic field. Furthermore, preciseknowledge of the magnetic field is essential to derive fundamental information about theenvironment surrounding different bodies in the solar system as well as to explore the interplanetaryspace. [...]

scholarly journals Measurements of the magnetic field in WD 1658+441

2013 ◽  
Vol 9 (S302) ◽  
pp. 402-403
Author(s):  
J. Ramírez Vélez ◽  
D. Hiriart ◽  
G. Valyavin ◽  
J. Valdez ◽  
F. Quiroz ◽  
...  
Keyword(s):  
Magnetic Field ◽  
White Dwarf ◽  
Longitudinal Magnetic Field ◽  
Field Measurements ◽  
Measured Variable ◽  
Preliminary Results ◽  
San Pedro ◽  
Magnetic Field Measurements ◽  
Object Of Study ◽  
The Magnetic Field

AbstractWe present the preliminary results of the measurements of longitudinal magnetic field of the massive white dwarf 1658+441. This star have an hydrogen pure atmosphere (e.g. Dupuis & Chayer, 2003). We have observed the target in a total of 18 hrs during 3 consecutive nights in June 2010 and one more in May 2011. The data was acquired with a prototypical spectropolarimeter at the San Pedro Martir Telescope in Mexico. We have tested the magnetic field measurements with our instrument using the famous Babcock's star obtaining consistent results with previous studies. For our object of study, the WD 1658+441, we have measured variable intensities of the longitudinal magnetic field of Blong = 720 kG that oscillates with an amplitude of 130 kG.

scholarly journals How many solar wind data are sufficient for accurate fluxgate magnetometer offset determinations?

2019 ◽  
Vol 8 (2) ◽  
pp. 285-291 ◽  
Author(s):  
Ferdinand Plaschke
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Measurements ◽  
Wind Data ◽  
Fluxgate Magnetometer ◽  
Time Intervals ◽  
Sensor Position ◽  
Magnetic Field Measurements ◽  
Wind Measurements ◽  
The Magnetic Field

Abstract. Accurate magnetic field measurements by fluxgate magnetometers onboard spacecraft require ground and regular in-flight calibration activities. Therewith, the parameters of a coupling matrix and an offset vector are adjusted; they are needed to transform raw magnetometer outputs into calibrated magnetic field measurements. The components of the offset vector are typically determined by analyzing Alfvénic fluctuations in the solar wind if solar wind measurements are available. These are characterized by changes in the field components, while the magnetic field modulus stays constant. In this paper, the following question is answered: how many solar wind data are sufficient for accurate fluxgate magnetometer offset determinations? It is found that approximately 40 h of solar wind data are sufficient to achieve offset accuracies of 0.2 nT, and about 20 h suffice for accuracies of 0.3 nT or better if the magnetometer offsets do not drift within these time intervals and if the spacecraft fields do not vary at the sensor position. Offset determinations with uncertainties lower than 0.1 nT, however, would require at least hundreds of hours of solar wind data.

scholarly journals High resolution magnetic field measurements in high-mass star-forming regions using masers

2016 ◽  
Author(s):  
Gabriele Surcis ◽  
Wouter H.T. Vlemmings ◽  
Huib Jan van Langevelde ◽  
Busaba Hutawarakorn Kramer
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Field Measurements ◽  
High Mass ◽  
Mass Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
Magnetic Field Measurements

Strong magnetic field of the peculiar red supergiant VY Canis Majoris

2017 ◽  
Vol 13 (S336) ◽  
pp. 391-392
Author(s):  
Hiroko Shinnaga ◽  
Mark J. Claussen ◽  
Satoshi Yamamoto ◽  
Shimojo Masumi
Keyword(s):  
Magnetic Field ◽  
Stellar Evolution ◽  
Field Measurements ◽  
Circumstellar Envelope ◽  
Magnetic Field Measurements ◽  
High Degree ◽  
The Magnetic Field ◽  
Very High ◽  
Measured Magnetic Field ◽  
Field Strengths

AbstractWe report on magnetic field measurements associated with the well-known extreme red supergiant (RSG), VY Canis Majoris (VY CMa). We measured both linear and circular polarization of the SiO v = 0, J = 1 − 0 transition using a sensitive radio interferometer. The measured magnetic field strengths are surprisingly high. A lower limit for the field strength is expected to be at least ~ 10 Gauss based on the high degree of linear polarization. Since the field strengths are very high, the magnetic field must be a key element in understanding the stellar evolution of VY CMa as well as the dynamical and chemical evolution of the complex circumstellar envelope of the star.

scholarly journals Ionospheric currents estimated simultaneously from CHAMP satelliteand IMAGE ground-based magnetic field measurements: a statisticalstudy at auroral latitudes

2004 ◽  
Vol 22 (2) ◽  
pp. 417-430 ◽  
Author(s):  
P. Ritter ◽  
H. Lühr ◽  
A. Viljanen ◽  
O. Amm ◽  
A. Pulkkinen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Local Time ◽  
Hall Current ◽  
Activity Index ◽  
Current System ◽  
Current Model ◽  
Field Measurements ◽  
Magnetic Field Measurements ◽  
Current Densities ◽  
The Magnetic Field

Abstract. One important contribution to the magnetic field measured at satellite altitude and at ground level comes from the external currents. We used the total field data sampled by the Overhauser Magnetometer on CHAMP and the horizontal magnetic field measurements of the IMAGE ground-based magnetometer network to study the ionospheric Hall current system in the auroral regions. For the CHAMP data a current model consisting of a series of lines and placed at a height of 110km is fitted to the magnetic field signature sampled on the passage across the polar region. The derived current distributions depend, among others, on season and on the local time of the satellite track. At dawn/dusk the auroral electrojets can be detected most clearly in the auroral regions. Their intensity and location are evidently correlated with the A E activity index. For a period of almost two years the results obtained from space and the currents determined from ground-based observations are studied. For the full IMAGE station array a newly-developed method of spherical elementary current systems (SECS) is employed to compute the 2-D equivalent current distribution, which gives a detailed picture of an area covering latitudes 60° – 80° N and 10° – 30° E in the auroral region. Generally, the current estimates from satellite and ground are in good agreement. The results of this survey clearly show the average dependence of the auroral electrojet on season and local time. This is particularly true during periods of increased auroral activity. The correlation coefficient of the results is close to one in the region of sizeable ionospheric current densities. Also the ratio of the current densities, as determined from above and below the ionosphere, is close to unity. It is the first time that the method of Hall current estimate from a satellite has been validated quantitatively by ground-based observations. Among others, this result is of interest for magnetic main field modelling, since it demonstrates that ground-based observations can be used to predict electrojet signatures in satellite magnetic field scalar data. Key words. Ionosphere (auroral Ionosphere; electric fields and currents; ionosphere-magnetosphere interactions)

scholarly journals Sunspot magnetic fields: a comparison between the CrAO and SDO/HMI data

2020 ◽  
Vol 1 (2) ◽  
pp. 1-5
Author(s):  
Regina Biktimirova ◽  
Valentina Abramenko
Keyword(s):  
Magnetic Field ◽  
Linear Regression ◽  
Linear Approximation ◽  
Pearson Correlation ◽  
Field Measurements ◽  
Maximum Modulus ◽  
Maximum Magnetic Field ◽  
Magnetic Field Measurements ◽  
The Relationship ◽  
The Magnetic Field

We performed a digitization of maximum magnetic field measurements in sunspots. The original data were acquired as drawings at the Crimean Astrophysical Observatory of the Russian Academy of Sciences (CrAO RAS). About 1000 sunspots observed in 2014 have been analyzed. The data were compared to the corresponding measurements from the SDO/HMI instrument (with both the line-of-sight magnetic field Bz(HMI) and the modulus of the magnetic field vector B(HMI)). For the same sunspot, the maximum modulus of the magnetic field derived at CrAO was compared to the corresponding value from HMI. The Crimean data and the space-based data (of both types) were found to be in direct proportion to each other. A linear approximation over the entire range of measurements (1–4) kilogauss (kG) shows a Pearson correlation coefficient of 0.71 (with the 95 % confidence boundaries of 0.68–0.74) and a slope of linear regression of 0.65±0.02 for both types of the space-based data. A linear approximation over the range of strong fields B(CrAO) > 1.8 kG gives a similar correlation, however the slope of linear regression is far closer to unity and constitutes 0.90 for the relationship (Bz(HMI) vs B(CrAO)) and 0.84 for the relationship (B(HMI) vs B(CrAO)). In the range of weak fields B(CrAO) < 1.8 kG, a non-linear deviation (exceeding) of the space-based data is observed. Non-linearity can be explained, in part, by a specific routine of the magnetic field measurements at CrAO, however further investigations are needed to explore sources of possible non-linearity in the HMI data. The Crimean measurements of the maximum magnetic field in sunspots are concluded to be in good agreement with the corresponding SDO/HMI measurements, and therefore they can be used for scientific purposes.

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