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Apparent and Intrinsic Evolution of Active Region Upflows  

Deb Baker   Submitted: 2017-02-21 01:52

We analyze the evolution of Fe XII coronal plasma upflows from the edges of ten active regions (ARs) as they cross the solar disk using the Hinode Extreme Ultraviolet Imaging Spectrometer (EIS). Confirming the results of Demoulin et al. (2013, Sol. Phys. 283, 341), we find that for each AR there is an observed long term evolution of the upflows which is largely due to the solar rotation progressively changing the viewpoint of dominantly stationary upflows. From this projection effect, we estimate the unprojected upflow velocity and its inclination to the local vertical. AR upflows typically fan away from the AR core by 40 deg. to near vertical for the following polarity. The span of inclination angles is more spread for the leading polarity with flows angled from -29 deg. (inclined towards the AR center) to 28 deg. (directed away from the AR). In addition to the limb-to-limb apparent evolution, we identify an intrinsic evolution of the upflows due to coronal activity which is AR dependent. Further, line widths are correlated with Doppler velocities only for the few ARs having the largest velocities. We conclude that for the line widths to be affected by the solar rotation, the spatial gradient of the upflow velocities must be large enough such that the line broadening exceeds the thermal line width of Fe XII. Finally, we find that upflows occurring in pairs or multiple pairs is a common feature of ARs observed by Hinode/EIS, with up to four pairs present in AR 11575. This is important for constraining the upflow driving mechanism as it implies that the mechanism is not a local one occurring over a single polarity. AR upflows originating from reconnection along quasi-separatrix layers (QSLs) between over-pressure AR loops and neighboring under-pressure loops is consistent with upflows occurring in pairs, unlike other proposed mechanisms acting locally in one polarity.

Authors: Deb Baker, Miho Janvier, Pascal Demoulin, Cristina Mandrini
Projects: None

Publication Status: Accepted Solar Physics
Last Modified: 2017-02-21 15:43
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FIP Bias Evolution in a Decaying Active Region  

Deb Baker   Submitted: 2015-01-30 02:59

Solar coronal plasma composition is typically characterized by first ionization potential (FIP) bias. Using spectra obtained by Hinode's EUV Imaging Spectrometer (EIS) instrument, we present a series of large-scale, spatially resolved composition maps of active region (AR) 11389. The composition maps show how FIP bias evolves within the decaying AR from 2012 January 4-6. Globally, FIP bias decreases throughout the AR. We analyzed areas of significant plasma composition changes within the decaying AR and found that small-scale evolution in the photospheric magnetic field is closely linked to the FIP bias evolution observed in the corona. During the AR's decay phase, small bipoles emerging within supergranular cells reconnect with the pre-existing AR field, creating a pathway along which photospheric and coronal plasmas can mix. The mixing time scales are shorter than those of plasma enrichment processes. Eruptive activity also results in shifting the FIP bias closer to photospheric in the affected areas. Finally, the FIP bias still remains dominantly coronal only in a part of the AR's high-flux density core. We conclude that in the decay phase of an AR's lifetime, the FIP bias is becoming increasingly modulated by episodes of small-scale flux emergence, i.e. decreasing the AR's overall FIP bias. Our results show that magnetic field evolution plays an important role in compositional changes during AR development, revealing a more complex relationship than expected from previous well-known Skylab results showing that FIP bias increases almost linearly with age in young ARs (Widing & Feldman, 2001, ApJ, 555, 426).

Authors: D. Baker, D. H. Brooks, P. Démoulin, S. L. Yardley, L. van Driel-Gesztelyi, D. M. Long, L. M. Green
Projects: Hinode/EIS

Publication Status: Accepted ApJ
Last Modified: 2015-02-03 10:59
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Plasma composition of a sigmoidal anemone active region  

Deb Baker   Submitted: 2013-10-03 08:54

Using spectra obtained by the EIS instrument onboard Hinode, we present a detailed spatially resolved abundance map of an active region (AR) - coronal hole (CH) complex that covers an area of 359 arcsec x  485 arcsec. The abundance map provides fi rst ionization potential (FIP) bias levels in various coronal structures within the large EIS fi eld of view. Overall, FIP bias in the small, relatively young AR is 2-3. This modest FIP bias is a consequence of the AR age, its weak heating, and its partial reconnection with the surrounding CH. Plasma with a coronal composition is concentrated at AR loop footpoints, close to where fractionation is believed to take place in the chromosphere. In the AR, we found a moderate positive correlation of FIP bias with nonthermal velocity and magnetic flux density, both of which are also strongest at the AR loop footpoints. Pathways of slightly enhanced FIP bias are traced along some of the loops connecting opposite polarities within the AR. We interpret the traces of enhanced FIP bias along these loops to be the beginning of fractionated plasma mixing in the loops. Low FIP bias in a sigmoidal channel above the AR's main polarity inversion line where ongoing flux cancellation is taking place, provides new evidence of a bald patch magnetic topology of a sigmoid/flux rope con guration.

Authors: D. Baker, D. H. Brooks, P. Demoulin, L. Gesztelyi, L. M. Green, J. Carlyle
Projects: Hinode/EIS

Publication Status: Accepted ApJ
Last Modified: 2013-10-05 20:20
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Forecasting a CME by Spectroscopic Precursor?  

Deb Baker   Submitted: 2011-11-21 03:42

This abstract was corrupted following database problems and is being recovered. It will be restored as quickly as possible. Any questions, please send them to Alisdair. Sorry for any incovenience.


Authors: D. Baker, L. van Driel-Gesztelyi, L.M. Green
Projects: Hinode/EIS

Publication Status: Accepted for publication by Solar Physics
Last Modified: 2011-11-22 02:49
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Abstracts by Author
Apparent and Intrinsic Evolution of Active Region Upflows
FIP Bias Evolution in a Decaying Active Region
Plasma composition of a sigmoidal anemone active region
Forecasting a CME by Spectroscopic Precursor?

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