On connecting the dynamics of the chromosphere and transition region with Hinode SOT and EIS
Viggo H.Hansteen, Bart De Pontieu, Mats Carlsson, Scott McIntosh, Tetsuya Watanabe, Harry Warren, Louise Harra, Hirohisa Hara, Theodore D. Tarbell, Dick Shine, Alan Title, Carolus J. Schrijver, Saku Tsuneta, Yukio Katsukawa, Kiyoshi Ichimoto, Yoshinori Suematsu, Toshifumi Shimizu
aa r X i v : . [ a s t r o - ph ] N ov PASJ:
Publ. Astron. Soc. Japan , 1– ?? , c (cid:13) On connecting the dynamics of the chromosphere and transition regionwith Hinode SOT and EIS.
Viggo H.
Hansteen
Bart
De Pontieu Mats
Carlsson Scott
McIntosh
Tetsuya
Watanabe Harry
Warren Louise
Harra Hirohisa
Hara Theodore D.
Tarbell Dick
Shine Alan
Title Carolus J.
Schrijver Saku
Tsuneta Yukio
Katsukawa Kiyoshi
Ichimoto Yoshinori
Suematsu Toshifumi
Shimizu Institute of Theoretical Astrophysics, University of Oslo, PB 1029 Blindern, 0315 Oslo Norway Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, CA 94304, USA Department of Space Studies, Southwest Research Insititute, 1050 Walnut St, Suite 400, Boulder, CO 80302, USA High Altitude Observatory, National Center for Atmospheric Research, PO Box 3000, Boulder, CO 80307, USA National Astronomical Observatory of Japan, Mitaka, Tokyo, 181-8588, Japan Space Science Division, Naval Research Laboratory, Washington DC, USA Mullard Space Science Laboratory, University College London, UK ISAS/JAXA, Sagamihara, Kanagawa, 229-8510, Japan (Received 2000 December 31; accepted 2001 January 1)
Abstract
We use coordinated Hinode SOT/EIS observations that include high-resolution magnetograms, chro-mospheric and TR imaging and TR/coronal spectra in a first test to study how the dynamics of the TR aredriven by the highly dynamic photospheric magnetic fields and the ubiquitous chromospheric waves. Initialanalysis shows that these connections are quite subtle and require a combination of techniques includingmagnetic field extrapolations, frequency-filtered time-series and comparisons with synthetic chromosphericand TR images from advanced 3D numerical simulations. As a first result, we find signatures of magneticflux emergence as well as 3 and 5 mHz wave power above regions of enhanced photospheric magnetic fieldin both chromospheric, transition region and coronal emission.
Key words:
Sun: chromosphere – Sun:transition region – Sun:corona – Sun: UV radiation – Sun: fluxemergence
1. Introduction
The Hinode spacecraft, launched in late September2006, is comprised of three scientific instruments (Kosugiet al. 2007): the Solar Optical Telescope (SOT), theExtreme ultraviolet Imaging Spectrograph (EIS), and theX-Ray Telescope (XRT). The SOT is designed to pro-duce high quality images and measurements of the mag-netic field in various photospheric and chromospheric linesand continua (Tsuneta et al. 2007). The ultraviolet andX-ray instruments are constructed to extract informa-tion from the outer solar atmosphere. In particular, EIS(Culhane et al. 2007) observes in two bands (180 −
205 ˚Aand 250 −
290 ˚A) that feature a number of coronal andsome transition region emission lines.An explicitly stated primary scientific goal of theHinode mission is to map and understand the transport ofmechanical energy flux between the lower lying layers ofthe Sun’s atmosphere and the corona, as well as the rela-tion between the structure of the photospheric magneticfield and coronal heating. Generally speaking there aretwo ways of transporting energy from the convection zoneand into the layers above: either by utilizing waves, suchas the 5-minute p-modes or chromospheric 3-minute oscil-lations, or by converting the energy contained in the mag- netic field, stressed by photospheric flows and granularevolution, in some episodic fashion into heat in the chro-mosphere and/or corona. Related questions are what rolemagnetic flux emergence plays in injecting energy into thechromosphere/corona and replenishing the previously ex-isting field; and with what efficiency acoustic and Alfv´enwaves are generated and propagated through the chro-mosphere and transition region. In this paper we reporton preliminary simultaneous observations made with theSOT and EIS instruments to shed light on these issues.
2. Instrumental setup and Observations
During a two-week period in February 2007 we observedseveral types of solar region including coronal hole, quietSun, network, and plage/small active regions both on thedisk and towards the solar limb. A substantial amount oftime was spent following the progress of the small activeregion NOAA 10942 as it transverses the disk from a solarposition of roughly −
400 arcsec to the west of disk centeron February 20 to a position of 900 arcsec east, near theeastern limb on February 27.With SOT we obtained magnetograms measured in theFe i . ii . −
11 s cadence) for the observations described here. The Hansteen et al. [Vol. ,Ca ii H-line filter used with SOT is fairly wide (0.22 nm)and thus includes a significant fraction of line wing inaddition to line core. We have collected similar imageseries in the G-band and in the blue continuum channelof SOT’s broad band filtergraph but those observationsare not described here.The EIS instrument also supports a number of observ-ing modes. We report on observations made with the40 arcsec wide slot that forms a 40 arcsec wide imageof the Sun in particular (strong) emission lines on thedetector. This observing mode has the advantage of al-lowing images to be recorded at relatively high cadence(30 s or so for the strongest lines), but incurs the costof removing any easily derived velocity or line-width sig-nal as well as a slightly worse spatial resolution that thatachieved with the 1 arcsec slit. We also report on rasterobservations made by stepping the 1 arcsec slit in 1 arcsecincrements across the region of interest. With exposuretimes of 30-60 s a typical raster takes of order an hour tocomplete. The spectral resolution of EIS is 0 . ix/x xii , as well as theTRACE 160.0 nm channel and the SOT Ca H-line.It must also be borne in mind that SOT has a cor-relation tracker that removes most of the orbital varia-tions on SOT pointing while EIS does not have such adevice: Flexing due temperature variations of the EIS in-strument during an orbit can be as large as 5 arcsec in thenorth/south direction and 2 −
3. Results
On February 19 2007, from roughly 11:30 to 17:30 weobserved a quiet Sun region that also contained weak plage
Fig. 1.
Co-pointed SOT and EIS images of a quiet Sun re-gion centered on heliocentric co-ordinates (280,0) arcsec ob-tained February 19, 2007. In the upper left panel we show aFe i ii ii xii of both polarities. In Figure 1 we show co-pointed indi-vidual frames from the SOT and EIS rasters that zoom inon the region observed with the SOT.In the upper left panel we show an image from the SOTmagnetogram movie. The field consists of several smallmagnetic elements of both polarities spread across the im-age. In addition, we find a stronger plage region stretch-ing from (255,-35) to (280,-5) in heliocentric coordinates.There is also some weaker plage centered at (270,15) and(283,45). In the movie the magnetic field, churned by themotions of the photosphere, shows motions of the individ-ual flux elements that presumably correspond to G-pointbright points as well as the bright points seen in the Ca ii H-line images. Flux elements of opposite polarity some-o. ] Connecting SOT and EIS 3
Fig. 2.
Co-pointed SOT and EIS images of a quiet Sun region centered on heliocentric co-ordinates (280,0) arcsec obtained February19, 2007. This set of images shows the time evolution of a cutout of the region shown in Figure 1 that illustrates the flux emergencethat occurs from roughly 14:45 UT to 15:30 UT (at which time the EIS time series completed). The top panels show Fe i ii ii xii times meet and merge, disappearing from view, at othertimes flux elements appear and move apart. In the weakplage regions of greater magnetic field concentration thefield seems less responsive to photospheric motions, oralternately photospheric motions are suppressed by thepresence of the field. The general topology of the plageis unchanged during the six hours this region of the Sunwas observed. We did however, observe an incidence offlux emergence in the central portion of the plage region;negative (black) field appears at (265,-25) just to the rightof the large collection of positive (white) field present infigure 1, rapidly splitting in two with one collection offield moving northeast and the other more or less stay-ing in place. This new flux is largely dissipated at theend of the time-series roughly one hour after it first ap-pears. Detailed images of the time evolution of the fluxemergence are shown in Figure 2.The magnetic topology outlined by the small plage re-gion is evident in all three of the wavelength bands shownin Figure 1.The Ca 396 . >
25 mHz)show that this haze corresponds to the ‘straws’ seen with0 . Fig. 3.
The upper panel shows the power frequency spec-trum for the variation of the logarithm of the intensity ∆
I/I for the He ii . that are weak because of the large photospheric contribu-tion to the wide Ca H filter used on SOT.)As seen in Figure 2 the region co-spatial with and/orjust above the region of flux emergence seen in the magne-togram movies initially shows a dimming in the Ca H-linefiltergrams. Flux is first seen to emerge in the magne- tograms at 14:44 UT. This is followed by what appear tobe two to three large dark granules in the Ca-H-line some10 minutes later at 14:55 UT. These dark granules expandand move with the emergence of the field. The border ofthis dark region becomes filled with bright points within20 minutes of the fields emergence. As time passes thedark granules brighten, seemingly as a result of ‘haze’ fill-ing in the dark region, which upon inspection of differ-ence and high-pass frequency filtered movies are revealedto consist of loop-like structures in the Ca-H-line that jointhe newly formed bright points.In the lower left panel of Figure 1 we show a raster im-age of the He ii xii ii and Fe xii lines were observed co-temporally with the SOT movies described above. Theseslot movies show large temporal variations at cadencesdown to those measurable by the 30 s exposure time; thegeneral topology outlined by the plage region is main-tained, also in the upper solar atmosphere, but the emis-sion is strongly variable at any given location both withinthe plage and outside in the weaker field quiet Sun. Thesevariations do not show an obvious one-to-one correspon-dence with events that are transpiring below: Some of themagnetic flux cancellations as two opposite polarity ele-ments coalesce are accompanied by brightening in the Heand Fe lines and some are not. The 3/5 minute wave pat-tern that is clearly discernible in the Ca H-line emissiondoes not leave an obvious footprint in the lines formedabove. An exception to this rule of non-correspondence isthe large flux emergence event that happens in the plage.As is clear by inspection of Figure 2 both the He ii and theFe xii lines show an dimming dark “bubble” that appearsat 15:14 UT and expands thereafter, almost 30 minutesafter the flux emergence is obvious in the magnetograms.Unfortunately, we did not observe the end of this eventwith EIS as another observing program was started at15:30 UT. While there were few obvious correlations between themovies made with SOT filtergrams and the EIS slot, aninitial insight into the role of waves can be found by con-sidering the power contained in the 3- and 5-minute fre-quency bands of this region in EIS He ii slot movies. Inthe upper panel of figure 3 we show the computed powerspectra of the variation of the intensity ∆ I/I for a subseto. ] Connecting SOT and EIS 5
Fig. 5.
South limb images made from rasters in the He ii xii ii line and that similar features appear in absorption in the Fe xii line. Axes are heliocentric co-ordinatesmeasured in arcseconds. of the brighter pixels found in the vicinity of the plageregion (solid line) and for a subset of pixels imaging typ-ical quiet Sun regions (dotted line). The spectra showsome excess power for the brighter region, in both 3 and5 minute bands, while the power found in the quiet Sunregion is of questionable significance. Note however, thatthe wave power found in the transition region is knownfrom SUMER observations ( e.g. McIntosh et al. 2001) tobe quite dependent on the topology of the magnetic fieldin the chromosphere below. Significant 5 minute power incoronal lines has been observed before with TRACE, e.g.,in the TRACE 17.1 nm and 19.5 nm bands in loops (deMoortel et al. 2002a; de Moortel et al. 2002b) as well as inthe moss (De Pontieu et al. 2003; De Pontieu et al. 2005).Likewise, 3 minute power in coronal emission above activeregions has also been seen before Brynildsen et al. (2000)in the TRACE 17.1 nm band.Maps of the location of the Fourier power of the in-tensity variation ∆
I/I of the He ii e.g. De Pontieu et al. 2004). However, identifi-cation of these intensity variations as wave-like as opposedto being a result of evolution (of e.g. the magnetic field)awaits the analysis of EIS velocities in sit-and-stare stud-ies with sufficiently high cadence. Future work involvingfield extrapolations based on the SOT magnetograms andtravel time analysis in the lower atmosphere will also benecessary to confirm this and/or to pin down the exactleakage mechanism.
While our slot movies and intensity raster maps do notshow any clear evidence of small scale features that can belinked with the lower atmosphere, velocity maps made inthe transition region He ii . ±
25 km/s relative to the average line shift,with black color indicating upward blue-shifts and whiteindicating down-flowing red-shifts. The velocities show afairly complex structure, and quite striking are the nu-merous intense ( >
25 km/s) blue-shifts found throughoutthe quiet Sun region of the images. (This type of event isfound in every raster made in the He ii line that includesquiet Sun emission during the two-week period covered bythis study). Note that the blue-shifts are not evident inthe 1 MK plasma imaged by the Fe xii line shown in thelower right panel. The linear extent of these phenomenais less than 1 arcsec . Note that that the S x blend knownto be located near the He ii line is on the red side of theHe ii line (and is visible to the red of the He ii line inspectra taken above the limb).The line profile of a typical up-flow event (solid line)along with the average line profile in the He ii Fig. 4.
The upper panel shows line profiles of the He ii xii ±
25 km/s. Axes are heliocentric co-ordinates measured inarcseconds.
Fig. 6.
Co-pointed SOT and EIS images of the small activeregion NOAA 10942 centered on solar co-ordinates (-430,-30)obtained February 20, 2007. In the upper left panel we show aFe i ii ii xii o. ] Connecting SOT and EIS 7to see whether we can find any correlations between themerging or appearance of magnetic elements and theseup-flow events seen in He ii , but our first impression isthat there is no one-to-one correspondence between theseevents. As an aside, we mention the possibility that there is aconnection between the up-flow events described here andthe He ii (macro)-spicules observed above the limb. Anexample is the EIS raster made on the southern pole limbon February 16 2007, shown in Figure 5. Similar spiculeshave been observed previously in the EUV passband bySOHO/SUMER (Wilhelm 2000). The observed “spicules”appear as largely radial features extending some 10 arc-sec above the limb with widths of order 1 − i.e. roughly the resolution of EIS). The spicules show up in ab-sorption in the Fe xii line: The bulk of the plasma in thisphenomena seems not to be heated to coronal tempera-tures. Note that the spicules are quite numerous, they arealso continually present in slot movies made on the samedate, but the lower resolution of the slot mode hindersaccurate identification and the measurement of lifetimes,birthrates or other properties, nor indeed correlation withthe Ca H-line spicules found above the limb. The difficulties in connecting phenomena in the lowersolar atmosphere with the transition region and coronais driven home by the extended set observations made ofNOAA 10942 made on February 20 (and every day there-after until February 27). In the photosphere this regiondisplays a large aggregate of (largely) unipolar field asshown in the upper left panel of Figure 6. The Ca H-lineimages, upper right panel, show enhanced emission in theplage region, presumably both from the photosphere andfrom the chromosphere above. A small pore is apparenttowards the lower part of the plage.It is very difficult to pick out the structure of the plageregion in images taken of the hotter plasma above, asshould be clear from the He ii xii xii extend eastward,apparently rooted in the western edge of the plage region.Note that also all the rasters made with the EIS instru-ment, including those shown in Figure 7 differ markedlyfrom each other. The He ii emission seems to mainly con-sist of shorter loops and perhaps hints of chromosphericnetwork (though the correlation with the Ca H-line emis-sion is poor in this example). The Si vii ii and Fe xii . The loops in this linemainly extend north-westward across the plage, the east-ward directed loops are partial, presumably footpoints ofthe hotter, eastward oriented, loops we find in Fe xii andin the Fe xv .
4. Conclusions
Both differences in instrument temporal and spatialresolution as well as fundamental differences betweenthe photosphere/chromosphere and the outer solar layerscomprising the transition region and corona are signifi-cant stumbling blocks in understanding the coupling be-tween these regions. Even though the Hinode spacecraftpresents us with tools of unprecedented sophistication forunravelling the complex of physical processes that controlthe outer layers of the Sun, a successful result will requireusing advanced analysis techniques. It is fortunate thatthese techniques are entering the scene concurrently withthe observations so as to make comparison between theoryand observation meaningful.Hinode is a Japanese mission developed and launchedby ISAS/JAXA, collaborating with NAOJ as domesticpartner, NASA and STFC (UK) as international partners.Scientific operation of the Hinode mission is conducted bythe Hinode science team organized at ISAS/JAXA. Thisteam mainly consists of scientists from institutes in thepartner countries. Support for the post-launch operationis provided by JAXA and NAOJ (Japan), STFC (U.K.),NASA (U.S.A.), ESA, and NSC (Norway). This workwas supported by the Norwegian Research Council grant170926.
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Fig. 7.
Intensity maps of NOAA 10942 made from EIS rasters on February 20, 2007. From left to right the lines shown are He ii vii xii xvxv