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Images of the Sun taken by the
Transition Region and Coronal Explorer

The TRACE images may be used without restrictions in publications of any kind. We appreciate an acknowledgement indicating that the Transition Region and Coronal Explorer, TRACE, is a mission of the Stanford-Lockheed Institute for Space Research, and part of the NASA Small Explorer program. More information on TRACE and other TRACE images can be found here.
M1.8 flare and loop oscillations in AR 9373

Equinox flare

On 21 March 2001, an M1.8 flare occurred in Active Region 9373, starting at 02:28UT, and peaking (in X-rays) around 02:37UT. The flare was associated with a spray of cool material (probably the result of the eruption of a small filament): material is thrown up to a height of approximately 50,000 km, and mostly slides back down again. More interestingly, however, is that the coronal loops seen over the solar edge are somehow driven to oscillate (see this QuickTime; JPEG compressed; 4.7MB) movie). The oscillations damp rapidly: only three to four back-and-forth swings are seen, with a period that appears to lie around 10 minutes. This phenomenon is very rare; it is interesting because these coronal quakes tell us things about the properties of the coronal magnetic field that are very hard to derive by other means.
AR9373; a field of pores
Active Region 9373 has a remarkably high content of sunspots and pores (the smaller equivalent of sunspots, without a surrounding penumbra). TRACE shows how these intense magnetic structures evolve on the solar surface: this 9.8MB QuickTime (JPEG compressed) 3-day white-light movie (March 13-16) shows (1) how the trailing spot fragmenting into pores, (2) how a spot just to the right of it fragments, temporarily tries to regroup, but then fragments after all, (3) the rapid forward motion of the leading sunspot on the right, and (4) several small new emergences of magnetic flux throughout the region. For the overall polarity structure, look at this SOHO/MDI high-resolution magnetogram. The field of view in the TRACE frames shown in the movie is approximately 180,000 by 94,000 km; the leading spot is about as large as the Earth:

Emergence and reconnection in AR9373/9374
An example of magnetic reconnection: Around 07:35UT on 14 March 2001, a relatively small magnetic bipole began to emerge next to the leading sunspot in Active Region 9373 (clearly seen in the 1600Å images taken by TRACE). Two hours later, a small jet-like feature is seen pointing towards Active Region 9374 southward of AR 9374 in the 171Å image. Just after midday (shown in the image to the left, taken around 12:33UT) a cusp-like structure (within the circles in the 171Å on the left and the 1600Å image on the right in this image) within the rapidly evolving corona over the new bipole points towards AR 9374 for over an hour. Faint, short-lived brightenings can be traced much of the way (parallel to the dashed line segment somewhat to the left of them in this image). Around 14UT, new loops are completely outlined between the newly emerged, now somewhat expanded region and the old region 9374.
Activation/eruption of a ring-shaped filament
TRACE observed this activation and partial eruption of a ring-shaped filament on 20 September 1998, around 02UT. The image on the left was taken in the 171Å passband, most sensitive to emission from plasma at temperatures around 1 million Kelvin, at 02:36:49UT, during the initial phases of the process. The image shows the outline of the dark filament in the back and the two ribbons at the footpoints of flaring loops in the front, together outlining the entire ring-shaped filament. The entire process is shonw in this QuickTime/JPEG-compressed movie (2.7MB; shown at half-resolution, with a field of view of 480 by 640 original pixels or 0.5 arcsec each; images rotated by 90 degrees clockwise so that north is to the right). The movie shows the postflare arcade of loops cooling into the TRACE 171Å passband first across the front of the filament, while the back part is lifting off to form a coronal mass ejection. After part of the ejected material slides under the arcade in the front, an arcade shows up in the back also, forming an almost complete doughnut-shaped ring around 4:30UT. Notice (a) that the initial flare ribbons form without obvious signs of a segment of the filament in the front having lifted off; (b) that the lower flare ribbon moves across the surface probably reflecting that successively higher loops are involved in a reconnection process.
Coronal rain
The heating of the corona frequently stops long enough along magnetic loops to cause them to cool rapidly, and to subsequently drain. TRACE sees the later stages of such cooling as the material (originally some 3-5 million Kelvin) cools into the 195Å passband (1.5 million Kelvin), then into the 171Å passband (1 million Kelvin) and subsequently into the CIV (1600Å) and Lyman alpha (1216Å) passbands characteristic of material at 100,000 Kelvin and below. This QuickTime/Cinepak movie (15.7MB) shows the evolution of cooling loops over Active Region 9004 on 26 May 2000, from 12 UT through 19 UT in 306 composite panels. The four panels (clockwise from top left) show the 171Å image, the ratio of 195Å to 171Å images, the ratio of 1216Å to 1600Å images, and the 1216Å image. The frames nearest in time to the 1216Å are collected in the combined images. The field of view is 640 by 480 pixels of 0.5 arcsec (~380 km) each, shown here binned to half resolution. The images are shown on a logarithmic gray scale (shown on the right of each panel) with ranges from 0.1 to 9.0 DN/sec/pixel, a ratio from 0.5 to 2, a ratio from 0.2 to 2.0, and from 1 to 20 DN/sec/pixel, respectively. The images have been rotated and mirrored, so that North is to the right, and West to the top. (The movie also appears in a study of loop cooling by C.J. Schrijver, published in Solar Physics, vol. 198, Issue 2, p. 325-345 (2001))
Sunspot flows and flares
This image shows a segment of a magnetically active region with some of the surrounding non-active Sun, observed by TRACE in the 1600Å passband (left) and the corresponding magnetic map (right) observed with SOHO/MDI on 9 November 1999. The TRACE image (10:13UT) shows as bright features the emission from gas at about 100,000 degrees over the magnetic-field concentrations on the solar surface, while the fainter emission is largely from gas at around 5,000 degrees at the surface. The sunspot shows up as a dark patch near the center of the image. The magnetic map, taken at 09:35UT, shows opposite polarities as green/blue/white and orange/red/black as strength increases. Note that the two small flares in progress in the TRACE image occur between regions of opposite polarity in the magnetic map. The (QuickTime; JPEG/A compressed; 1.2MB) movie shows the evolution of these flares, from 09:59:16UT through 10:49:18UT. Notice also the streaming of bright features in from the center of the sunspot across its so-called moat. Although it seems as if field concentrations are moving away from the spot, there is rarely a measurable change in the field surrounding the spot. Consequently, hypotheses have been postulated that we are seeing waves rather than actual objects moving almost radially from the spot. Despite decades of study, the nature of these ``moving magnetic features'' remains obscure. The bright pixels that show up near the end of the movie show where the camera was hit by energetic particles as TRACE moves towards the Earth's magnetic pole. The black bands in some of the images occur whenever a small package of information is lost in the transmission of data from the spacecraft to the groundstation.
Cooling loops
Now you see them, now you don't. The rapid cooling of loops, and the associated draining of material from them in episodes of coronal rain, have been shown in these images several times. Often that is the only way to actually see the structure of the magnetic field. This movie (QuickTime; photo-JPEG compressed; 1.3MB; field of view is 640 by 480 pixels of 375 km each, reduced to half size in the movie compared to the single still image; rotated so that north is to the left) shows the evolution of a set of cooling loops, from 05:55UT through 08:10UT on 3 September 1999, observed in the 171Å passband of TRACE seeing emission from gas around one million degrees). But notice how difficult it is to guess what is going on: are loops moving as they cool, or do we see successive loops cool into and out of the temperature interval that TRACE can see? Notice also that the rapid loop cooling is associated with substantial brightening of a set of footpoints; but why on only one side? Should we look for the other footpoints in the leading sunspot? By the way: the black bands in some of the images occur whenever a small package of information is lost in the transmission of data from the spacecraft to the groundstation.
Full Sun in 171Å (TRACE)
Full Sun in Ca II K (BBSO) Full Sun in H alpha (BBSO)
Three views of the Sun taken on 8 February 2001: the image on the left is a low-resolution version of a full-disk mosaic of TRACE 171Å (one million degrees) images; the central image shows the Sun in the light of singly ionized Calcium (CaIIK; most sensitive to emission originating around 10,000 degrees); the image on the right is taken in the light of the hydrogen Balmer alpha (Ha) line, which is formed over a range of temperatures up to some 20,000 degrees. Notice that the patches of magnetic field that light up in the CaIIK image also show up bright in the Ha image; these show the lower parts of the solar magnetic field that higher up form the arches (coronal loops) in the TRACE image on the left. The dark filaments that show up in the Ha image can be vaguely recognized in the TRACE image because the filaments absorb the extreme ultraviolet emission from any part of the corona behind it; the filaments are too cool and tenuous to show up in the CaIIK image. The two images on the right were taken at the Big Bear Solar Observatory.
AR9334 in 195Å
AR9334 in 1600Å AR9334 in white light
These three images are of Active Region 9334 taken by TRACE on February 9th, 2001 at about 03:32UT. The 195Å image (left; gold) shows the coronal gas that has a temperature close to 1.5 million degrees. The white light image (right; gray) shows the sunspots as seen on the solar surface, also know as the photosphere; temperatures range from about 4000 Kelvin in the spot cores to 5700 Kelvin at the brightest areas. The sunspots, which form whenever there are substantial areas of concentrated magnetic field, are also seen in the 1600Å image (center; red). That image also shows the many bright patches of emission that identify the location of concentrations of magnetic field that are not large enough to form dark spots. Temperatures in this 1600Å image range from 5000 degrees in the spots to 100,000 degrees in the brightest patches. The field of view is 500 arcseconds of 725 km; the dark circle is not the edge of the Sun, but rather vignetting that occurs by the filterwheels in the telescope. Courtesy Dawn Myers.
Flare: coming through

Magnetic map (MDI)
The flare that went off in the magnetic region to the left just before the start of the TRACE 171Å movie (QuickTime; photo-JPEG compressed; 2.9MB; field of view is 640 by 480 pixels of 375 km each of cooling loops, from 06UT through 07:30UT on 2 September 1999, observed in the 171Å passband of TRACE seeing emission from gas around one million degrees) causes ``moss'' to form in the center of the image as material impacts the lower atmosphere from below. But notice how little magnetic field (lower image on the left, taken at 17:35UT, showing opposite polarities as green/blue/white and orange/red/black as strength increases) there is below the moss for the active-region field to connect to. Also notice that the reorganizing magnetic field, largely invisible to TRACE, somehow pushes the loop fan just southward of the moss out of the way.

Other TRACE images in this collection: Set 1, 2, 3, 4, 5, 6, 7, 8, 9, 10.

See also a collection of images related to the Sun, other cool stars, and solar-terrestrial effects


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