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THE IMPACT OF A FILAMENT ERUPTION ON NEARBY HIGH-LYING COOL LOOPS  

Louise Harra   Submitted: 2014-09-01 05:08

The first spectroscopic observations of cool Mgii loops above the solar limb observed by NASA?s Interface Region Imaging Spectrograph (IRIS) are presented. During the observation period, IRIS is pointed off-limb, allowing the observation of high-lying loops, which reach over 70 Mm in height. Low-lying cool loops were observed by the IRIS slit-jaw camera for the entire four-hour observing window. There is no evidence of a central reversal in the line profiles, and the Mg ii h/k ratio is approximately two. TheMg ii spectral lines show evidence of complex dynamics in the loops with Doppler velocities reaching ?40 km s-1. The complex motions seen indicate the presence of multiple threads in the loops and separate blobs. Toward the end of the observing period, a filament eruption occurs that forms the core of a coronal mass ejection. As the filament erupts, it impacts these high-lying loops, temporarily impeding these complex flows, most likely due to compression. This causes the plasma motions in the loops to become blueshifted and then redshifted. The plasma motions are seen before the loops themselves start to oscillate as they reach equilibrium following the impact. The ratio of the Mg h/k lines also increases following the impact of the filament

Authors: Harra, Matthews, Long, Doschek and De Pontieu
Projects: None

Publication Status: published
Last Modified: 2014-09-03 13:12
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Spectroscopic observations of a coronal Moreton wave  

Louise Harra   Submitted: 2011-08-02 04:26

We observed a coronal wave (EIT wave) on 2011 February 16, using EUV imaging data from the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) and EUV spectral data from the Hinode/EUV Imaging Spectrometer (EIS). The wave accompanied an M1.6 flare that produced a surge and a coronal mass ejection (CME). EIS data of the wave show a prominent redshifted signature indicating line-of-sight velocities of ~20 km s-1 or greater. Following the main redshifted wave front, there is a low-velocity period (and perhaps slightly blueshifted), followed by a second redshift somewhat weaker than the first; this progression may be due to oscillations of the EUV atmosphere set in motion by the initial wave front, although alternative explanations may be possible. Along the direction of the EIS slit the wave front's velocity was ~500 km s-1, consistent with its apparent propagation velocity projected against the solar disk as measured in the AIA images, and the second redshifted feature had propagation velocities between ~200 and 500 km s-1. These findings are consistent with the observed wave being generated by the outgoing CME, as in the scenario for the classic Moreton wave. This type of detailed spectral study of coronal waves has hitherto been a challenge, but is now possible due to the availability of concurrent AIA and EIS data.

Authors: Harra, Sterling, Gömöry, Veronig
Projects: None

Publication Status: published
Last Modified: 2011-08-02 14:59
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The Solar Source of a Magnetic Cloud Using a Velocity Difference Technique  

Louise Harra   Submitted: 2010-11-03 03:52

For large eruptions on the Sun, it is often a problem that the core dimming region cannot be observed due to the bright emission from the flare itself. However, spectroscopic data can provide the missing information through the measurement of Doppler velocities. In this paper we analyse the well-studied flare and coronal mass ejection that erupted on the Sun on 13 December 2006 and reached the Earth on 14 December 2006. In this example, although the imaging data were saturated at the flare site itself, we could extract information on the core dimming region through velocity measurements, as well as on the remote dimmings. The purpose of this paper is to determine more accurately the magnetic flux of the solar source region, potentially involved in the ejection, through a new technique. The results of its application are compared to the flux in the magnetic cloud observed at 1AU, as a way to check the reliability of this technique. We analysed data from the {it Hinode} EUV Imaging Spectrometer to estimate the Doppler velocity in the active region and its surroundings before and after the event. This allowed us to determine a Doppler velocity 'difference' image. We used the velocity difference image overlayed on a Michelson Doppler Imager magnetogram to identify the regions in which the blue-shifts were more prominent after the event; the magnetic flux in these regions was used as a proxy for the ejected flux and compared to the magnetic cloud flux. This new method provides a more accurate flux determination in the solar source region.

Authors: Harra, Mandrini, Dasso, Gulisano, Steed and Imada
Projects: Hinode/EIS

Publication Status: Solar Physics, accepted
Last Modified: 2010-11-03 08:53
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Response of the Solar Atmosphere to the Emergence of "Serpentine" Magnetic Field  

Louise Harra   Submitted: 2010-04-26 06:58

Active region magnetic flux that emerges to the photosphere from below will show complexity in the structure, with many small-scale fragmented features appearing in between the main bipole and then disappearing. Some fragments seen will be absorbed into the main polarities and others seem to cancel with opposite magnetic field. In this paper we investigate the response of the corona to the behaviour of these small fragments and whether energy through reconnection will be transported into the corona. In order to investigate this we analyse data from the Hinode space mission during flux emergence on 1 ? 2 December 2006. At the initial stages of flux emergence several small-scale enhancements (of only a few pixels size) are seen in the coronal line widths and diffuse coronal emission exists. The magnetic flux emerges as a fragmented structure, and coronal loops appear above these structures or close to them. These loops are large-scale structures ? most small-scale features predominantly stay within the chromosphere or at the edges of the flux emergence. The most distinctive feature in the Doppler velocity is a strong ring of coronal outflows around the edge of the emerging flux region on the eastern side which is either due to reconnection or compression of the structure. This feature lasts for many hours and is seen in many wavelengths. We discuss the implications of this feature in terms of the onset of persistent outflows from an active region that could contribute to the slow solar wind.

Authors: L. K. Harra, T. Magara, H. Hara, S. Tsuneta, T. J. Okamoto and A. J. Wallace
Projects: Hinode/EIS

Publication Status: in press
Last Modified: 2010-04-26 09:12
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Coronal nonthermal velocity following helicity injection before an X-class flare  

Louise Harra   Submitted: 2009-01-13 01:17

We explore the ''pre-flare'' behavior of the corona in the three-day period building up to the X-class flare on 2006 Dec 13, by analyzing the EUV spectral profiles from the Hinode EUV Imaging Spectrometer (EIS) instrument. We found an increase in the coronal spectral line widths, beginning after the time of saturation of the injected helicity as measured by citet{magara}. In addition, this increase in line widths (indicating non-thermal motions) starts before any eruptive activity occurs. Hinode EIS has the sensitivity to measure changes in the build up to a flare many hours before the flare begins.

Authors: Harra, Williams, Wallace, Magara, Hara, Tsuneta, Sterling and Doschek
Projects: Hinode/EIS

Publication Status: published
Last Modified: 2009-01-14 08:47
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Subject will be restored when possible  

Louise Harra   Submitted: 2008-03-26 02:00

The formation of the slow solar wind has been debated for many years. In this paper we show evidence of persistent outflow at the edges of an active region as measured by the EUV Imaging Spectrometer onboard Hinode. The Doppler velocity ranged between 20-50 km s-1 and was consistent with a steady flow seen in the X-ray Telescope. The latter showed steady, pulsing outflowing material and some transverse motions of the loops. We analyse the magnetic field around the active region and produce a coronal magnetic field model. We determine from the latter that the outflow speeds adjusted for line-of-sight effects can reach over 100 km s-1. We can interpret this outflow as expansion of loops that lie over the active region, which may either reconnect with neighbouring large-scale loops or are likely to open to the interplanetary space. This material constitutes at least part of the slow solar wind.

Authors: Harra, Sakao, Mandrini,Hara, Imada, Young, van Driel-Gesztelyi, Baker
Projects: Hinode/EIS

Publication Status: ApJ Letters, 676, L147, 2008
Last Modified: 2008-09-23 21:12
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Subject will be restored when possible  

Louise Harra   Submitted: 2007-09-11 08:21

Coronal dimming has been a signature used to determine the source of plasma that forms part of a coronal mass ejection (CME) for many years. Generally dimming is detected through imaging instruments such as SOHO EIT by taking difference images. Hinode tracked active region 10930 from which there were a series of flares. We combine dimming observations from EIT with Hinode data to show the impact of flares and coronal mass ejections on the region surrounding the flaring active region, and we discuss evidence that the eruption resulted in a prolonged steady outflow of material from the corona. The dimming region shows clear structure with extended loops whose footpoints are the source of the strongest outflow (approx 40 km s-1). This confirms that the loops that are disrupted during the event do lose plasma and hence are likely to form part of the CME. This is the first time the velocity of the coronal plasma has been measured in an extended dimming region away from the flare core. In addition there was a weaker steady outflow from extended, faint loops outside the active region before the eruption, which is also long lasting. These were disturbed and the velocity increased following the flare. Such outflows could be the source of the slow solar wind.

Authors: Harra, Hara, Imada, Young, Williams, Sterling, Korendyke and Attrill
Projects: Hinode

Publication Status: PASJ, in press
Last Modified: 2007-09-12 06:36
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Flows in the Solar Atmosphere due to the eruptions on the 15th July, 2002  

Louise Harra   Submitted: 2005-05-27 01:58

Which kind of flows are present during flares? Are they compatible with the present understanding of energy release and which model best describes the observations? We analyze successive flare events in order to answer these questions. The flares were observed in the magnetically complex NOAA active region (AR) 10030 on 15 July 2002. One of them is of GOES X-class. The description of these flares and how they relate to the break-out model is presented in Gary and Moore (cite{Gary04}). The Coronal Diagnostic Spectrometer on board SOHO observed this active region for around 14 hours. The observed emission lines provided data from the transition region to the corona with a field of view covering more than half of the active region. In this paper we analyse the spatially resolved flows seen in the atmosphere from the preflare to the flare stages. We find evidence for evaporation occurring before the impulsive phase. During the main phase, the ongoing magnetic reconnection is demonstrated by upflows located at the edges of the flare loops (while downflows are found in the flare loops themselves). We also report the impact of a filament eruption on the atmosphere, with flows up to 300 km s-1 observed at transition-region temperatures in regions well away from the location of the pre-eruptive filament. Our results are consistent with the predictions of the break out model before the impulsive phase of the flare; while, as the flare progresses, the directions of the flows are consistent with flare models invoking evaporation followed by cooling and downward plasma motions in the flare loops.

Authors: L. K. Harra, P. Demoulin, C. Mandrini, S.A. Matthews, L. van Driel-Gesztelyi, J.L. Culhane, L. Fletcher
Projects: Soho-CDS

Publication Status: A&A in press
Last Modified: 2005-05-27 01:58
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Evidence of flaring in a transequatorial loop on the Sun  

Louise Harra   Submitted: 2003-10-22 07:59

We present evidence for flaring behaviour in a transequatorial loop (TEL) that lights up in soft X-rays on the 13th July 2000. The large loop structure connects active regions NOAA 9070/9066 in the northern hemisphere and NOAA 9069/9068 in the southern hemisphere. We follow the loop systems for 2 days and observe several pieces of evidence strongly suggesting flare behaviour of the form seen in standard flaring in active regions. These include brightenings of the loop structure, cooling of plasma which is seen both in soft X-rays and in the transition region temperatures, morphological evidence of reconnection inflow, and blue-shifts around the footpoint of the TEL suggestive of chromospheric evaporation. We present, to our knowledge for the first time, observations of TEL in the OV emission line.

Authors: Harra, Matthews and van Driel-Gesztelyi
Projects: None

Publication Status: in press, ApJ Letters
Last Modified: 2003-10-22 07:59
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The association of transequatorial loops in the solar corona with coronal mass ejection onset  

Louise Harra   Submitted: 2003-02-20 05:28

It has been shown that transequatorial loops can disappear in association with the onset of a coronal mass ejection (CME) (Khan & Hudson 2000). We extend this result by considering a larger sample of transequatorial loop systems (TLS) to investigate their associated flaring and CME activity. We find 10 of a total 18 TLS considered here to be associated with flaring and CME onset originating from a connected active region. A total 33 cases of flaring and associated CME onset are observed from these 10 systems during their lifetime. We observe the influence of this activity on the TLS in each case. In contrast to the Khan & Hudson result, we find evidence that transequatorial loop eruption leading to soft X-ray brightening equivalent in temperature to a B-class flare is equally as common as dimming in the corona. Consequently we conclude that the scenario observed by Khan & Hudson is not universal and that other types of CME-TLS association occur. It was found that for transequatorial loops that were associated with CMEs the asymmetry in longitude was larger than for those that were not associated to a CME by 10 . In addition, the extent in latitude (as a measure of the loop length) was nearly twice as large for those TLS associated with CMEs than those that were not. The asymmetry in latitude was actually on average larger for those TLS not associated with CMEs, than for those that were. This suggests that di erential rotation is not a major contributor to the production of CMEs from transequatorial loops. Instead it is more likely for a CME to be produced if the loop is long, and if there is a large asymmetry in longitude. The implications of these results for CME onset prediction are discussed.

Authors: Glover, A., Harra., L.K., Matthews, S.A., Foley, C.A.
Projects:

Publication Status: In press (&A)
Last Modified: 2003-02-20 05:28
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Imaging and Spectroscopic Investigations of a Solar Coronal Wave: Propertiesofthe Wave Front and Associated Erupting Material.  

Louise Harra   Submitted: 2003-01-29 08:22

Using spectral data from the Coronal Diagnostic Spectrometer (CDS) instrument on the Solar and Heliospheric Observatory (SOHO) spacecraft, we observe a coronal wave feature (often referred to as an ``EIT wave'') which occurred in association with a solar eruption and flare on 1998 June~13. EUV images from the Transition Region and Coronal Explorer (TRACE) satellite show that the coronal wave consists of two aspects: (1) a ``bright wave,'' which shows up prominently in the TRACE difference images, moves with a velocity of approximately 200 kms, and is followed by a strong dimming region behind it, and (2) a ``weak wave,'' which is faint in the TRACE images, has a velocity of about 500 kms, and appears to disperse out of the bright wave. The weak wave passes through the CDS field of view, but shows little or no line-of-sight motions in CDS spectra (velocities less than about 10 kms). Only a small portion of the bright wave passes the CDS field of view, with the spectral lines showing insignificant shifts. A ``high-velocity'' CDS feature, however, occurs after the weak wave passes, which appears to correspond to ejection of cool, filament-like material in TRACE images. Our observations have similarities with a numerical simulation model of coronal waves presented by Chen etal~(2002), who suggests that coronal waves consist of a faster-propagating, piston-driven portion, and a more slowly-propagating portion due to the opening of field lines associated with an erupting filament.

Authors: Louise Harra & Alphonse Sterling
Projects:

Publication Status: In press
Last Modified: 2003-01-29 08:22
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Abstracts by Author
THE IMPACT OF A FILAMENT ERUPTION ON NEARBY HIGH-LYING COOL LOOPS
Spectroscopic observations of a coronal Moreton wave
The Solar Source of a Magnetic Cloud Using a Velocity Difference Technique
Response of the Solar Atmosphere to the Emergence of ?Serpentine? Magnetic Field
Coronal nonthermal velocity following helicity injection before an X-class flare
Subject will be restored when possible
Subject will be restored when possible
Flows in the Solar Atmosphere due to the eruptions on the 15th July, 2002
Evidence of flaring in a transequatorial loop on the Sun
The association of transequatorial loops in the solar corona with coronal mass ejection onset
Imaging and Spectroscopic Investigations of a Solar Coronal Wave: Propertiesofthe Wave Front and Associated Erupting Material.

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