Penumbral-like Structures in the Photosphere as a Manifestati on of Flux Emergence

1Dipartimento di Fisica e Astronomia – Università di Catania, Italy2INAF – Osservatorio Astrofisico di Catania, Italy

14th European Solar Physics MeetingTrinity College, Dublin, 8 – 12 September 2014

S a l v o L . G u g l i e l m i n o 1 , F r a n c e s c a Z u c c a r e l l o 1 & P a o l o R o m a n o 2

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A complete study of magnetic flux emergence, interaction, and diffusion should take into account some “anomalies”

In the photosphere we can observe flux concentrations over many spatial scales

sunspots, pores, ephemeral regions, granular loops …but rare observations also show:

orphan penumbrae and naked sunspots

Magnetic flux emergence

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Orphan penumbrae are bundles of filamentary structures, very similar to sunspot penumbral filaments, but that are not adjacent to any sunspot umbra

Why “orphan penumbrae”?

The orphan penumbra shows the same motions observed in the sunspot penumbra

Zirin & Wang (1991)

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Formation mechanism a)photospheric manifestation

of a flux rope trapped in the photosphere (Kuckein et al., 2012a,b)

b)the result of an emerging Ω-loop trapped in the photosphere by overlying canopy fields (Lim et al., 2013)

c)the effect of submerging horizontal field in flattened Ω-loops (Jurčak et al., 2014)

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Models of penumbral filament formation

MHD simulations (Rempel 2012): magnetoconvection in presence of horizontal fields is able to form penumbral structures when a magnetic canopy overlies the flux region

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Observations of penumbral filament formation

Romano et al. (2013, 2014) find a 3"-5" width annular zone around a pore, a few hours before the penumbra formation

•magnetic field with uncombed structure•several patches

(≈1") with upflows and rather vertical fieldsThe penumbral filament formation results from the bending

of the field lines of the magnetic canopy overlying the pore

See our poster!!!

High resoluti on observati ons of the formati on of a sunspot penumbra

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Answer: evolution and spectropolarimetry

LARGE orphan penumbrae in NOAA 11089

Zuccarello et al. (2014) ApJ, 787, 57

SMALL orphan penumbra inNOAA 11391

Guglielmino et al. (2014)ApJL, 786, L22

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NOAA 11089

• Visible from 2010 July 20 to July 30• SDO – DOT – HINODE observations: July 22-24• Recurrent AR (5 passages on the solar disk)

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SDO full-disk observations

• The orphan penumbrae are visible for more than 48 hours and are larger than umbral regions

• The structures fragment during their evolution• These SDO observations show that:

the eastern orphan penumbra is formed as the main sunspots lose part of their penumbrae

the western orphan penumbra is forming independently

• In both the structures the SDO movie indicates several episodes of flux emergence

• Peculiar motions are found in the orphan penumbrae:– upflows in their central regions

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DOT observations

Note the sequence of bright granules at the border of the orphan penumbra

Note the chromospheric filamentary structure above the orphan penumbraIn the chromosphere we find upflows in the central part of the structure

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HINODE/SP observations

Maps of physical parameters from the standard M-E Hinode CSAC inversions (level 1.5 data)Azimuth ambiguity was solved using the Non-Potential Field Calculation (Georgoulis, 2005)Line-of-sight (LOS) velocities were calibrated assuming plasma at rest in umbraeRaster scans aligned through cross-correlation algorithms Asymmetry

in Stokes profiles

“uncombed” structure!!!

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HINODE/SP evolution

Red contours: Polarity Inversion Lines (PILs)Dark blue/blue contours (upflow): -3/-1.5 km s-1

Red/light red contours (downflow): +3/+1.5 km s-1

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HINODE/SP evolution• Peculiar plasma flows are found in the western

orphan penumbra: a central upward motion and downflows at the edges, max values -4 / +6 km s-1

• Flows last for ≈ 8 hours and decrease in time The upflowing region seems to fragment the penumbra Downflows are observed until the end of Hinode observations

• Evershed flows in the orphan penumbra filaments?• This structure lies above a PIL, with a maximum

horizontal field of ≈ 1500 G decreasing in time• Magnetic field lines show a “direct configuration”,

with a very homogeneous azimuth angle

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NOAA 11391

• Visible from 2012 January 3 to January 13• SDO – HINODE observations: January 10-12• Decaying AR (2 passages on the solar disk)

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G band: photospheric evolution

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HINODE/SP parameters

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Ca II H: chromospheric evolution

• Lim et al. (2013) found a magnetic canopy over the filaments and an Hα brightening at one of the edge of the structure

• Indirect confirmation of the presence of the magnetic canopy– interaction between the positive patch of the emerging bipole

and the plage negative field– presence of a strong Ca II H brightening likely due to magnetic

reconnection between these two flux systems

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HINODE results• The penumbral filaments form after the emergence

of an ephemeral region, that gives rise to two pores• The emergence zone has upflows of ≈ 1 km s-1 and an

average horizontal field of ≈ 650 G• The penumbral filaments form after about 2 hours

and slightly move eastwards with respect to the AR• The region has an average field of ≈ 1000 G and lies

above a S-shaped PIL, where line-of-sight motions of about ±2 km s-1 occur (inversion and Doppler)

• No evidence of a flux rope above the structure• Interaction with an overlying canopy

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Summary

• NOAA 11089 shows the presence of large areas– 23" x 5" – covered by orphan penumbrae that have a lifetime of days and fragment during their evolution

• The magnetic field lines have different inclinations along the line of sight, indicating an uncombed structure

• The orphan penumbrae show upflows in the central part and downflows at the edges, lasting for hours and decreasing in time

• The magnetic field vector has a strong horizontal component in the western orphan penumbra, that lies above a PIL

• NOAA 11391 show the presence of penumbral-like filaments near the leading sunspot above a PIL

• Above these structures magnetic reconnection with the overlying canopy fields occurs at low chromospheric levels

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Formation mechanism a)photospheric manifestation

of a flux rope trapped in the photosphere (Kuckein et al., 2012a,b)

b)the result of an emerging Ω-loop trapped in the photosphere by overlying canopy fields (Lim et al., 2013)

c)the effect of submerging horizontal field in flattened Ω-loops (Jurčak et al., 2014)

The combination of the horizontal fields of emerging Ω-loops and an overlying canopy

can give rise to the observed structures