scholarly journals No universal connection between the vertical magnetic field and the umbra-penumbra boundary in sunspots

2020 ◽  
Vol 639 ◽  
pp. A106
Author(s):  
B. Löptien ◽  
A. Lagg ◽  
M. van Noort ◽  
S. K. Solanki
Keyword(s):  
Magnetic Field ◽  
Statistical Analysis ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Filling Factor ◽  
Spot Size ◽  
Vertical Magnetic Field ◽  
Continuum Intensity ◽  
The Mean ◽  
The Continuum

Context. It has been reported that the boundary between the umbra and the penumbra of sunspots occurs at a canonical value of the strength of the vertical magnetic field, independently of the size of the spot. This critical field strength is interpreted to be the threshold for the onset of magnetoconvection. Aims. Here we investigate the reasons why this criterion, also called the Jurčák criterion in the literature, does not always identify the boundary between the umbra and the penumbra. Methods. We performed a statistical analysis of 23 sunspots observed with Hinode/SOT. We compared the properties of the continuum intensity and the vertical magnetic field between filaments and spines and how they vary between spots of different sizes. Results. We find that the inner boundary of the penumbra is not related to a universal value of the vertical magnetic field. The properties of spines and filaments vary between spots of different sizes. Both components are darker in larger spots and the spines exhibit a stronger vertical magnetic field. These variations of the properties of filaments and spines with the spot size are also the reason for the reported invariance in the averaged vertical magnetic field at 50% of the mean continuum intensity. Conclusions. The formation of filaments and the onset of magnetoconvection are not related to a canonical value of the strength of the vertical magnetic field. The seemingly unique magnetic field strength is rather an effect of the filling factor of spines and penumbral filaments.

scholarly journals Magnetic properties of a long-lived sunspot

2018 ◽  
Vol 620 ◽  
pp. A104 ◽  
Author(s):  
M. Schmassmann ◽  
R. Schlichenmaier ◽  
N. Bello González
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Field Component ◽  
Active Regions ◽  
Magnetic Field Component ◽  
Stable Phase ◽  
Vertical Magnetic Field ◽  
Continuum Intensity ◽  
The Magnetic Field

Context. In a recent statistical study of sunspots in 79 active regions, the vertical magnetic field component Bver averaged along the umbral boundary is found to be independent of sunspot size. The authors of that study conclude that the absolute value of Bver at the umbral boundary is the same for all spots. Aims. We investigate the temporal evolution of Bver averaged along the umbral boundary of one long-lived sunspot during its stable phase. Methods. We analysed data from the HMI instrument on-board SDO. Contours of continuum intensity at Ic = 0.5Iqs, whereby Iqs refers to the average over the quiet sun areas, are used to extract the magnetic field along the umbral boundary. Projection effects due to different formation heights of the Fe I 617.3 nm line and continuum are taken into account. To avoid limb artefacts, the spot is only analysed for heliocentric angles smaller than 60°. Results. During the first disc passage, NOAA AR 11591, Bver remains constant at 1693 G with a root-mean-square deviation of 15 G, whereas the magnetic field strength varies substantially (mean 2171 G, rms of 48 G) and shows a long term variation. Compensating for formation height has little influence on the mean value along each contour, but reduces the variations along the contour when away from disc centre, yielding a better match between the contours of Bver = 1693 G and Ic = 0.5Iqs. Conclusions. During the disc passage of a stable sunspot, its umbral boundary can equivalently be defined by using the continuum intensity Ic or the vertical magnetic field component Bver. Contours of fixed magnetic field strength fail to outline the umbral boundary.

scholarly journals Multifractal structure of the large-scale heliospheric magnetic field strength fluctuations near 85AU

2004 ◽  
Vol 11 (4) ◽  
pp. 441-445 ◽  
Author(s):  
L. F. Burlaga
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Large Scale ◽  
Solar Maximum ◽  
Multifractal Spectrum ◽  
The Sun ◽  
Heliographic Latitude ◽  
The Mean ◽  
The Magnetic Field

Abstract. During 2002, the Voyager 1 spacecraft was in the heliosphere between 83.4 and 85.9AU (1AU is the mean distance from the Sun to Earth) at 34° N heliographic latitude. The magnetic field strength profile observed in this region had a multifractal structure in the range of scales from 2 to 16 days. The multifractal spectrum observed near 85AU is similar to that observed near 40AU, indicating relatively little evolution of the multifractal structure of the magnetic field with increasing distance in the distant heliosphere in the epoch near solar maximum.

An investigation of hydrodynamic waves with a cylindrical microwave resonator. III. The influence of an axial magnetic field

1969 ◽  
Vol 47 (10) ◽  
pp. 1051-1055
Author(s):  
F. L. Curzon ◽  
R. L. Pike
Keyword(s):  
Magnetic Field ◽  
Surface Wave ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Axial Magnetic Field ◽  
Microwave Resonator ◽  
Hydrodynamic Waves ◽  
Vertical Magnetic Field

A microwave resonator has been employed to study the damping of a surface wave on mercury in the presence of a vertical magnetic field. The conditions of the experiment satisfy the linearity requirements of the theory and confirm the expected dependence of the damping frequency on magnetic field strength, fluid depth, and radius.

Some comments about correlations between magnetic field and velocity, magnetic field and line intensity in the undisturbed photosphere

1968 ◽  
Vol 35 ◽  
pp. 236-239
Author(s):  
G. Y. Vassilyeva ◽  
A. K. Tchandaev
Keyword(s):  
Magnetic Field ◽  
Velocity Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Correlation Functions ◽  
Cross Correlation ◽  
Absolute Value ◽  
Field Recordings ◽  
The Mean ◽  
The Magnetic Field

Test cross-correlation functions between the magnetic field recordings and the sight-line velocity recordings with East and West relative lag for two regions near the centre of the disk have been computed. We have also found the deviations of the absolute value of the magnetic-field strength |H| from the mean absolute value of magnetic-field strength |H̄| for the whole region. The same procedure for the velocity field has been made. The cross-correlation functions for these deviations have also been computed (Figure 1).

scholarly journals The magnetic nature of umbra–penumbra boundary in sunspots

2018 ◽  
Vol 611 ◽  
pp. L4 ◽  
Author(s):  
J. Jurčák ◽  
R. Rezaei ◽  
N. Bello González ◽  
R. Schlichenmaier ◽  
J. Vomlel
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Field Component ◽  
Vertical Component ◽  
Vertical Magnetic Field ◽  
Intensity Threshold ◽  
The Magnetic Field ◽  
Magnetic Nature

Context. Sunspots are the longest-known manifestation of solar activity, and their magnetic nature has been known for more than a century. Despite this, the boundary between umbrae and penumbrae, the two fundamental sunspot regions, has hitherto been solely defined by an intensity threshold. Aim. Here, we aim at studying the magnetic nature of umbra–penumbra boundaries in sunspots of different sizes, morphologies, evolutionary stages, and phases of the solar cycle. Methods. We used a sample of 88 scans of the Hinode/SOT spectropolarimeter to infer the magnetic field properties in at the umbral boundaries. We defined these umbra–penumbra boundaries by an intensity threshold and performed a statistical analysis of the magnetic field properties on these boundaries. Results. We statistically prove that the umbra–penumbra boundary in stable sunspots is characterised by an invariant value of the vertical magnetic field component: the vertical component of the magnetic field strength does not depend on the umbra size, its morphology, and phase of the solar cycle. With the statistical Bayesian inference, we find that the strength of the vertical magnetic field component is, with a likelihood of 99%, in the range of 1849–1885 G with the most probable value of 1867 G. In contrast, the magnetic field strength and inclination averaged along individual boundaries are found to be dependent on the umbral size: the larger the umbra, the stronger and more horizontal the magnetic field at its boundary. Conclusions. The umbra and penumbra of sunspots are separated by a boundary that has hitherto been defined by an intensity threshold. We now unveil the empirical law of the magnetic nature of the umbra–penumbra boundary in stable sunspots: it is an invariant vertical component of the magnetic field.

scholarly journals Fluctuations of the magnetic-field strength of sunspots within one day

1968 ◽  
Vol 35 ◽  
pp. 214-214
Author(s):  
H. Künzel
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
General Tendency ◽  
Mean Error ◽  
The Mean ◽  
Short Time ◽  
The Magnetic Field ◽  
Field Strengths

In the period of May-June 1965, the magnetic-field strengths of twenty sunspots were measured in order to investigate fluctuations within one day. The results of spectrograms, which were taken in the interval of one hour, are given in graphs. The mean error of one value has the size of ± 169 gauss. The graphs show the general tendency in the behaviour of field strength. Fluctuations of magnetic-field strength up to 800 gauss within a few hours were found. The short-time fluctuations shown in the graphs are mostly smaller than the mean error and therefore probably not real.For more details see Astron. Nachr., 289 (1967), 233.

scholarly journals The Influence of A Magnetic Field on Radiative Damping of Magnetoatmospheric Oscillations

1998 ◽  
Vol 185 ◽  
pp. 423-426
Author(s):  
Dipankar Banerjee ◽  
S.S. Hasan ◽  
J. Christensen-Dalsgaard
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Weak Magnetic Field ◽  
Vertical Magnetic Field ◽  
Radiative Effects ◽  
Newton’S Law ◽  
Damping Rate ◽  
Moderate Field ◽  
Radiative Damping

We investigate the influence of a magnetic field on the radiative damping of magnetoatmospheric waves, extending our previous work on the adiabatic modes of an isothermal stratified atmosphere with a uniform vertical magnetic field. Banerjee, Hasan & Christensen-Dalsgaard (1996, 1997) generalized this work to include radiative effects using Newton's law of cooling for a weak magnetic field. The present study examines the variation of the mode damping rate with increasing magnetic field strength. We find that a moderate field suppresses radiative damping.

scholarly journals The Mean Magnetic Field Strength of CI Tau

2020 ◽  
Vol 888 (2) ◽  
pp. 116 ◽  
Author(s):  
Kimberly R. Sokal ◽  
Christopher M. Johns-Krull ◽  
Gregory N. Mace ◽  
Larissa Nofi ◽  
L. Prato ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
The Mean

Granular cells in the presence of magnetic field

2016 ◽  
Vol 12 (S327) ◽  
pp. 34-39
Author(s):  
J. Jurčák ◽  
B. Lemmerer ◽  
M. van Noort
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Statistical Study ◽  
Line Of Sight ◽  
Active Region Noaa ◽  
Granular Cells ◽  
The Mean ◽  
Convective Cells ◽  
The Magnetic Field

AbstractWe present a statistical study of the dependencies of the shapes and sizes of the photospheric convective cells on the magnetic field properties. This analysis is based on a 2.5 hour long SST observations of active region NOAA 11768. We have blue continuum images taken with a cadence of 5.6 sec that are used for segmentation of individual granules and 270 maps of spectropolarimetric CRISP data allowing us to determine the properties of the magnetic field along with the line-of-sight velocities. The sizes and shapes of the granular cells are dependent on the the magnetic field strength, where the granules tend to be smaller in regions with stronger magnetic field. In the presence of highly inclined magnetic fields, the eccentricity of granules is high and we do not observe symmetric granules in these regions. The mean up-flow velocities in granules as well as the granules intensities decrease with increasing magnetic field strength.

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