The Photospheric Flow near the Flare Locations of Active Regions

2000 ◽  
Vol 179 ◽  
pp. 249-250
Author(s):  
Debi Prasad Choudhary
Keyword(s):  
Magnetic Field ◽  
Active Regions ◽  
Field Of View ◽  
Image Motion ◽  
Line Center ◽  
Flare Activity ◽  
Data Set ◽  
Zero Crossing ◽  
Left And Right ◽  
The Magnetic Field

Extended AbstractThe observation of the photospheric velocity field along with the magnetic field is very important for understanding the origin and evolution of these locations of active regions. Earlier measurements have shown a general down flow with velocities of 0.2 to 0.3 km s−1in the active regions along with few locations of upflows. The localised upflows are observed in the light bridges and emerging flux regions with different speeds (Beckers & Schröter 1969). The flow patterns of flare locations in the active regions are observed by using the tower vector magnetograph (TVM) of Marshall Space Flight Centre. The line-center-magnetogram (LCM) technique has been employed to determine the active region velocities (Giovanelli & Ramsay 1971). The LCM is based on finding the wavelength in the line profile where two opposite circularly polarised Zeeman-split components change sign. If the material in the magnetic field of different locations have relative line of sight velocities, their cross-over wavelength will be seen to be Doppler shifted. In order to use the LCM with TVM, a series of Stoke-V images are made as a function of wavelength and their cross-over wavelength at each pixel is determined. We have observed 12 active regions between June 25th and August 25th, 1998. Three of these active regions (NOAA 8253, 8264 and 8307) show flare activity associated with the flux emergence and/or changes in magnetic shear during their disk passage. The images of a selected field of view in left and right circularly polarised Zeeman components in the wavelength range of 5250.12 to 5250.30 Å are obtained at 10 mÅ steps. The time taken for obtaining one set of observations is about 10–15 minutes. In this mode of operation, the start and end wavelengths are specified and the filter is tuned at desired wavelength steps. In one observing sequence, two sets of left and right circularly polarized images are produced as a function of wavelength. These sets of images are processed and merged following a certain procedure to produce a data cube. The most important requirement for the Doppler shift measurements is the repeatability of the wavelength steps. In the recent improvement, the filter tuning was achieved with accuracy better than 0.3 mÅ by using an optical encoder. However, it has been shown that insufficient spectral resolution would lead to spurious zero-crossing shift of asymmetric Stokes-V. This effect of spectral smearing in the case of observations with TVM and the present data analysis procedure has been estimated by simulation. The individual images are flat fielded and registered in order to remove the pixel sensitivity variation over the field of view and image motion during the observations. The two Zeeman components are subtracted to obtain a set of difference images as a function of wavelength. These processed images are merged to make Stokes-V data cubes, with two spatial and one-wavelength dimensions. The integrated Stokes-V profiles are obtained by averaging the profiles of the pixels with magnetic field values higher than a certain cut-off value depending on the noise level in each data set.

scholarly journals EUV Line Intensities and the Magnetic Field in Solar Active Regions

2001 ◽  
Vol 203 ◽  
pp. 276-279
Author(s):  
J. Ireland ◽  
A. Fludra
Keyword(s):  
Magnetic Field ◽  
Extreme Ultraviolet ◽  
Active Regions ◽  
Central Meridian ◽  
Coronal Emission ◽  
Data Set ◽  
Line Intensities ◽  
Doppler Imager ◽  
Synoptic Observations ◽  
The Magnetic Field

The Coronal Diagnostic Spectrometer (CDS) on SOHO carries out daily synoptic observations of the Sun in four EUV (extreme ultraviolet) spectra: He I 584 Å, O V 630 Å, Mg IX 368 Å and Fe XVI 360 Å, over a 4 arcmin-wide strip along the solar central meridian. Using 53 active regions observed in this data set along with co-temporally observed SOHO-MDI (Michelson Doppler Imager) magnetograms we study the correlation of the chromospheric, transition region and coronal emission with the photospheric magnetic field for meridional active regions, probing the relation between the radiative output and magnetic observables. We also establish empirical, quantitative relations among intensities of different lines, and between intensities and the magnetic field flux.

scholarly journals Sunspot Proper Motion and Flare Frequency

1995 ◽  
Vol 151 ◽  
pp. 45-46
Author(s):  
G. Csepura ◽  
L. Győri ◽  
A.A. Galal
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Proper Motion ◽  
Active Regions ◽  
Field Configuration ◽  
Flare Activity ◽  
Magnetic Field Configuration ◽  
Spot Group ◽  
The Magnetic Field ◽  
Flare Frequency

Flare activity of solar active regions is generally believed to depend on a sheared configuration of magnetic fields (Hagyard et al. 1984). There are cases when the shear necessary for a flare can be attributed to the emergence of a new flux in the spot group (Wang 1992). But, perhaps, a newly born active region can also influence the magnetic field configuration in a nearby active region (Poleto et al. 1993, Gesztelyi et al. 1993). In this paper we are interested primarily in the influence of a newly emerging spot group on a nearby one.The three neighbouring active regions NOAA AR 6412(B-C), 6413(A) and 6415(D) have been studied between 13-22 December 1990. White-light pictures for studying sunspot proper motion and area evolution were taken at Gyula Observing Station (Hungary), Debrecen Heliophysical Observatory (Hungary) and Helwan Observatory (Egypt). Times and positions of the flares were taken from the Solar Geophysical Data (No. 558, part 1, February 1991).

scholarly journals Spiral-shaped wavefronts in a sunspot umbra

2019 ◽  
Vol 621 ◽  
pp. A43 ◽  
Author(s):  
T. Felipe ◽  
C. Kuckein ◽  
E. Khomenko ◽  
I. Thaler
Keyword(s):  
Magnetic Field ◽  
Active Regions ◽  
Field Vector ◽  
Doppler Velocity ◽  
Data Set ◽  
Magnetic Field Topology ◽  
Magnetoacoustic Waves ◽  
Fabry Perot ◽  
Field Lines ◽  
The Magnetic Field

Context. Solar active regions show a wide variety of oscillatory phenomena. The presence of the magnetic field leads to the appearance of several wave modes whose behavior is determined by the sunspot thermal and magnetic structure. Aims. We aim to study the relation between the umbral and penumbral waves observed at the high photosphere and the magnetic field topology of the sunspot. Methods. Observations of the sunspot in active region NOAA 12662 obtained with the GREGOR telescope (Observatorio del Teide, Tenerife, Spain) were acquired on 2017 June 17. The data set includes a temporal series in the Fe I 5435 Å line obtained with the imaging spectrograph GREGOR Fabry-Pérot Interferometer (GFPI) and a spectropolarimetric raster map acquired with the GREGOR Infrared Spectrograph (GRIS) in the 10 830 Å spectral region. The Doppler velocity deduced from the restored Fe I 5435 Å line has been determined, and the magnetic field vector of the sunspot has been inferred from spectropolarimetric inversions of the Ca I 10 839 Å and the Si I 10 827 Å lines. Results. A two-armed spiral wavefront has been identified in the evolution of the two-dimensional velocity maps from the Fe I 5435 Å line. The wavefronts initially move counterclockwise in the interior of the umbra, and develop into radially outward propagating running penumbral waves when they reach the umbra-penumbra boundary. The horizontal propagation of the wavefronts approximately follows the direction of the magnetic field, which shows changes in the magnetic twist with height and horizontal position. Conclusions. The spiral wavefronts are interpreted as the visual pattern of slow magnetoacoustic waves which propagate upward along magnetic field lines. Their apparent horizontal propagation is due to their sequential arrival to different horizontal positions at the formation height of the Fe I 5435 Å line, as given by the inclination and orientation of the magnetic field.

scholarly journals Coherence Analysis of Photospheric Line Parameters in Active and Non-Active Solar Regions

1993 ◽  
Vol 141 ◽  
pp. 36-39
Author(s):  
Arnold Hanslmeier ◽  
Wolfgang Mattig ◽  
Anastasios Nesis
Keyword(s):  
Magnetic Field ◽  
Phase Shift ◽  
Active Regions ◽  
Line Center ◽  
Coherence Analysis ◽  
Velocity Fluctuations ◽  
Continuum Intensity ◽  
The Magnetic Field

AbstractExamples of coherence functions between continuum intensity and line center velocity fluctuations are discussed for non active and active regions. It seems that the magnetic field leads to a different phase shift between intensity and velocity fluctuations than for non active regions.

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.

scholarly journals Nonlinear force-free modeling of magnetic fields in flare-productive active regions

2015 ◽  
Vol 11 (S320) ◽  
pp. 167-174
Author(s):  
M. S. Wheatland ◽  
S. A. Gilchrist
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Boundary Data ◽  
Numerical Solutions ◽  
Free Field ◽  
Active Regions ◽  
Coronal Magnetic Field ◽  
Nonlinear Force ◽  
The Magnetic Field ◽  
Force Free Field

AbstractWe review nonlinear force-free field (NLFFF) modeling of magnetic fields in active regions. The NLFFF model (in which the electric current density is parallel to the magnetic field) is often adopted to describe the coronal magnetic field, and numerical solutions to the model are constructed based on photospheric vector magnetogram boundary data. Comparative tests of NLFFF codes on sets of boundary data have revealed significant problems, in particular associated with the inconsistency of the model and the data. Nevertheless NLFFF modeling is often applied, in particular to flare-productive active regions. We examine the results, and discuss their reliability.

scholarly journals Cusp-like plasma in high altitudes: a statistical study of the width and location of the cusp from Magion-4

2002 ◽  
Vol 20 (3) ◽  
pp. 311-320 ◽  
Author(s):  
J. Mĕrka ◽  
J. Šafránková ◽  
Z. Nĕmeček
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
High Altitudes ◽  
Data Set ◽  
Latitudinal Dependence ◽  
Merging Process ◽  
Low Altitude ◽  
Field Lines ◽  
The Magnetic Field ◽  
Dipole Tilt

Abstract. The width of the cusp region is an indicator of the strength of the merging process and the degree of opening of the magnetosphere. During three years, the Magion-4 satellite, as part of the Interball project, has collected a unique data set of cusp-like plasma observations in middle and high altitudes. For a comparison of high- and low-altitude cusp determination, we map our observations of cusp-like plasma along the magnetic field lines down to the Earth’s surface. We use the Tsyganenko and Stern 1996 model of the magnetospheric magnetic field for the mapping, taking actual solar wind and IMF parameters from the Wind observations. The footprint positions show substantial latitudinal dependence on the dipole tilt angle. We fit this dependence with a linear function and subtract this function from observed cusp position. This process allows us to study both statistical width and location of the inspected region as a function of the solar wind and IMF parameters. Our processing of the Magion-4 measurements shows that high-altitude regions occupied by the cusp-like plasma (cusp and cleft) are projected onto a much broader area (in magnetic local time as well as in a latitude) than that determined in low altitudes. The trends of the shift of the cusp position with changes in the IMF direction established by low-altitude observations have been confirmed.Key words. Magnetospheric physics (magnetopause, cusp and boundary layer; solar wind – magnetosphere interactions)

A Surprising Result: “Bulk” SiC Defects in the Negative Bias Instability in 4H-SiC MOSFETs

2016 ◽  
Vol 858 ◽  
pp. 513-517 ◽  
Author(s):  
Mark A. Anders ◽  
Patrick M. Lenahan ◽  
Aivars J. Lelis
Keyword(s):  
Magnetic Field ◽  
Elevated Temperature ◽  
Negative Bias ◽  
Surprising Result ◽  
Zero Crossing ◽  
Electrically Detected Magnetic Resonance ◽  
G Value ◽  
Bias Temperature Stress ◽  
Bias Instability ◽  
The Magnetic Field

We utilize electrically detected magnetic resonance and “on-the-fly” elevated temperature stressing to examine the effects of negative bias temperature stress on defects within the “bulk” SiC, that is, below the SiC/SiO2 interface. We observe generation of two temperature-dependent defects; one has a two (or three) line spectrum with lines separated by about 61 (30) Gauss when the SiC/SiO2 interface is perpendicular to the magnetic field and very slightly less, about 59 (30) Gauss when the SiC/SiO2 interface is parallel to the field. The second spectrum has a single line with zero-crossing g = 2.0118 when the magnetic field is nearly perpendicular to the SiC/SiO2 interface; the g-value drops to about 2.0016 with the field parallel to the SiC/SiO2 interface. We also observe strong evidence for hydrogen motion within the “bulk” SiC, as both spectra broaden significantly at elevated temperature, with broadening at both high and low fields and frequencies.

Influence of time-variable solar wind on the response of Mercury’s magnetosphere

2021 ◽  
Author(s):  
Sae Aizawa ◽  
Nicolas André ◽  
Ronan Modolo ◽  
Elisabeth Werner ◽  
Jim Slavin ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Charged Particles ◽  
Time Variable ◽  
Low Energy ◽  
Field Of View ◽  
Plasma Measurement ◽  
Electrons And Ions ◽  
Low Energy Electrons ◽  
The Magnetic Field

<p><span lang="EN-GB">BepiColombo is going to conduct its first Mercury flyby in October 2021. During this flyby,  plasma measurement will be obtained and bring new insights on the Hermean magnetosphere and its interaction with the Sun despite the limited field of view of the instruments during the cruise phase. Unlike Mariner-10 ion measurements will be obtained, and unlike MESSENGER, low energy electrons and ions will be measured simultaneously. In this study, we have revisited Mariner 10 and MESSENGER observations with the help of the global hybrid model LatHyS in order to understand the influence of time-variable solar wind and to constraint the plasma environment. We are able to reproduce the magnetic field observations of Mariner 10 along its trajectory with in particular two distinct signatures consisting of a quiet and disturbed state of the magnetosphere. In addition, the plasma spectrogram is also collected in the model and this enables us to detail the properties of the charged particles observed during the flyby. We will discuss all these signatures both in term of an interaction with a time-variable solar wind and localized processes occurring in the magnetosphere. We will then present the virtual sampling of both the magnetic field and plasma spectrogram along BepiColombo’s first Mercury flyby trajectory and discuss the possible signatures to be observed at that time.</span></p>

scholarly journals Magnetic Shear and Nonpotential Energy Evolution of Solar Minimum and the Onset of Solar Cycle 23

2001 ◽  
Vol 203 ◽  
pp. 267-269
Author(s):  
J. Dun ◽  
H. Zhang ◽  
B. Zhang ◽  
R. Li
Keyword(s):  
Solar Cycle ◽  
Relative Number ◽  
Transverse Field ◽  
Active Regions ◽  
Shear Angle ◽  
Magnetic Shear ◽  
Data Set ◽  
Solar Cycle 23 ◽  
Sunspot Relative Number ◽  
The Magnetic Field

Using a 1995-1998 data set of vector magnetograms, the magnetic field flux, shear angle of the transverse field and nonpotential energy of active regions were calculated. The evolution of these parameters were analyzed together with time series of the solar monthly sunspot relative number and area to study their relationships in the ascending phase of solar cycle 23. We find the magnetic flux and nonpotential energy have a good correlation with sunspot relative number and area. But the magnetic shear angle does not develop as above indices.

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