Kinematics and magnetic properties of a light bridge in a decaying sunspot
M. Falco1, J. M. Borrero2, S.L. Guglielmino1, P. Romano3, R. Schlichenmaier2, F. Zuccarello1, S. Criscuoli4, A. Cristaldi5, I. Ermolli5, L. Rouppe Van Der Voort6
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1Dipartimento di Fisica e Astronomia – Università di Catania, Italy 2KIS – Kiepenheuer-Institut fur Sonnenphysik, Freiburg, Germany
3INAF – Osservatorio Astrofisico di Catania, Italy 4NSO-National Solar Observatory, Sunspot, USA
5INAF – Osservatorio Astronomico di Roma, Italy 6ITA, University of Oslo, Norway
What is a Light Bridge?
A bright and elongated structure delineating the borders between dark umbral fragments.
Observed during:
Classification:
• the assembly process of a sunspot • the decay phase of a sunspot
• LBs segmented along their length by tiny granules separated by narrow dark lanes oriented perpendicular to the axis of the bridges
• LBs unsegmented more resembling the elongated bright filaments seen in the penumbra
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Properties of the LBs
Magnetoconvection origin
vs
Convection penetrating from the sub-photospheric layers into a field-free gap
Plasma motions: previous observations showed evidence of sinking plasma in the axial channel Convective origin of the LBs.
Rimmele (2008): upflows in the dark lane and downflows on both sides of it
Magnetic Field: field strength lower and more horizontal than in the umbra. LBs are a discontinuity in the regular umbral field
2nd SOLARNET Meeting. Palermo (Italy), 2-5 February 2015
6-19 August 2011, La Palma (Canary Islands)
S. Criscuoli (PI), I. Ermolli, S. L. Guglielmino, A.Cristaldi, M. Falco, F. Zuccarello
Observational Campaign at the Swedish Solar Telescope (SST)
2nd SOLARNET Meeting. Palermo (Italy), 2-5 February 2015
Observational Campaign data-set Instrument Wavelength Spectral
points Pixel size
(arcsec)
Time Resolution
(sec)
Observation days
SST Fe I 5576 Å 20 0.0592 28 6 - 19 Aug 2011
Fe I pair 6302 Å 15 0.0589 28 6 - 19 Aug 2011
Ca II H core 1 0.0338 9 6 - 19 Aug 2011
DOT G band - 0.071 30
7 - 19 Aug 2011 Hα 7 0.109 30
Hinode
G band 1 0.108
6 Aug 2011 Ca II H 1 0.108
Mg I at 5172 Å (I/V) 2 Fe I pair 6302 Å (SP) 140 0.32 5 maps in 3 h
SDO HMI continuum - 0.5 720 2 - 7 Aug 2011
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HMI/SDO on August 6, 2011
NOAA 11263
Coord: N16 W43 (621",188")
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NOAA 11263 evolution: HMI continuum 3-Aug-2011 09:58:25 UT
5-Aug-2011 09:58:25 UT
4-Aug-2011 09:58:25 UT
6-Aug-2011 09:58:25 UT SST FOV
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NOAA 11263: SST data
Wide Band 5576 Å with FOV 57.5 x 57.8 arcseconds (41700 x 41900 Km)
Light Bridge
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CRISP Continuum - Fe I 5576 Line
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Ca II H core
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Hinode filtergrams
NOAA 11263, Ca II H line NOAA 11263, G-band
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SST and Hinode data-set inversion
The results obtained from the inversion confirm for both dataset that the magnetic field strength in the LB is lower than in the umbra and is
comparable with that of the penumbra
Hinode inversion SST/CRISP inversion
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Hinode: Magnetic components
The longitudinal magnetic field is weaker in the LB, while the horizontal magnetic field is stronger in this area
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Hinode: Inclination and Azimuth angles
In the LB the magnetic field inclination ranges between
-30 and -70 degrees
The azimuth map shows a discontinuity in the site
hosting the LB
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We used SIR inversion code (Stokes Inversion based on Response functions) to obtain: map of the temperature; map of the velocity; map of the total magnetic field
We inverted the Fe I line at 6301.5 Å and Fe I line at 6302.5 Å at the same time using: weight (=1) for Stokes I and more weight (=4) for Stokes Q, U,
V; 2 nodes for temperature; 1 node for all the other physical parameter (velocity, magnetic
field, azimuth, inclination); fixed microturbulence (=0.0); fixed macroturbulence (=2.95).
SIR Inversion Code
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SIR Inversion: LB Analysis
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LB Intensity
(2)
(1)
Different granular area and intensity along the dark lane
Intensity of large grains: 1.1 Intensity of small grains: 0.8
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LB Magnetic Field
(2)
(1)
2
1
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LB Temperature
(2)
(1)
2
1
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2
1
Parameter Dark Lane LB large granulation
LB small granulation
Intensity (Ic) (Fe I 6302 Å)
0.8 1.1 0.8
Magnetic Field (Fe I 6302 Å)
1500 G 700 - 1000 G 1500 G
Size (arcsec) 0’’.3 0’’.8 0’’.2
Results
There are differences in intensity and magnetic field between the DL and the small and large LB granulation
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Dark Lane Analysis
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In the LBs the LOS velocity values are between 0.7 and -0.2 km/s
In the LBn the LOS velocity values can reach up to -0.9 km/s
Conclusions (1)
The DL of the LBs shows both downflows and upflows The DL of the LBn is characterized by upflows
The strong surrounding magnetic field plays a fundamental role not only in the formation of a cusp-like region with enhanced
density and corresponding to the dark lane, but also in the vertical upflow
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Convection penetrating from the sub-photospheric layers into a field-free gap
The results of the SIR inversion confirm that where the magnetic field is lower, convection is more effective and the
intensity of the grains of the LB is higher
Conclusions (2)
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This research work has received funding from the European Commission’s Seventh Framework Programme under the
grant agreements no. 284461 (eHEROES project), no. 312495 (SOLARNET project), no. 606862 (F-Chroma
project). This research is also supported by the ITA MIUR-PRIN grant on “The active sun and its effects on space and Earth climate" and by Space WEather Italian COmmunity
(SWICO) Research Program.