During the August 11, 1999 Total Solar Eclipse
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During the August 11, 1999 Total Solar Eclipse |
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On August 11, 1999, a total solar eclipse occurred in central Europe, the Middle East, and India. A partial eclipse was visible from the north-eastern US, Europe, north Africa, and west Asia. On July 28, 1999, we performed an MHD computation of the solar corona to predict what the solar corona would look like during the eclipse. We used photospheric magnetic field data from Carrington rotation 1951 (corresponding to the dates June 24 - July 21, 1999) from the National Solar Observatory at Kitt Peak. Our prediction was published on this Web Page prior to the eclipse. Below we compare our prediction with two images of the eclipse.
Terrestrial north is up
Predicted polarization brightness (pB) in the solar corona for August 11, 1999, at 11:38 UT (corresponding to totality in Eastern Turkey). The state of the solar corona was computed using a 3-D magnetohydrodynamic (MHD) simulation. The pB signal is produced by white light scattered off electrons in the coronal plasma. The image has been radially detrended to account for the fall-off of coronal brightness with distance from the Sun. Vertical (top) is terrestrial (geocentric) north. This is the view of the Sun that would be seen by an observer on Earth with a camera aligned so that vertical is toward the Earth's north pole. To view this image in a coordinate system aligned with solar north, click here. Click the image to see it in more detail.
Predicted polarization brightness (left) together with traces of the magnetic field lines (right), in the solar corona also for August 11, 1999, at 11:38 UT. The Sun's surface shows color contours of the radial component of the measured photospheric magnetic field from Kitt Peak National Solar Observatory, showing the location of active regions (strong magnetic fields). Click the images for high-resolution pictures. To view these images in a coordinate system aligned with solar north, click here.
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(courtesy of Wendy Carlos*) |
Polarization Brightness |
Magnetic Field Lines |
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In the figures above we compare our MHD model prediction with a photograph taken in Romania. The eclipse image is a computer composite and optimization from five negatives taken with radially graded filters by Wendy Carlos and Jonathan Kern. The images have terrestrial (geocentric) north vertically upward. *Eclipse Image: © 1996-2000 Wendy Carlos - All Rights Reserved. For details, see http://www.wendycarlos.com/eclipse.html.
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(courtesy of Fred Espenak*) |
Polarization Brightness |
Magnetic Field Lines |
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In the figures above we compare our MHD model prediction with a photograph taken in Turkey. The eclipse image was constructed by adding 22 separate photographs taken at different exposures to compensate for the rapid radial fall-off of the brightness in the corona, and was digitally processed to enhance the fine details of the corona. The images have terrestrial (geocentric) north vertically upward. *Eclipse Image: © 1999 by Fred Espenak, courtesy of www.MrEclipse.com.
It can be noted from the comparisons above that the prediction at this time when the Sun is very active (during the ascending phase of the solar cycle close to solar maximum) is not as accurate as our previous predictions at solar minimum. This may be due to several reasons, including the fact that the Sun's magnetic field was changing rapidly at this time. It would therefore be expected that using out-of-date magnetic fields to predict coronal structure would be less accurate. In addition, the limited spatial resolution of our calculation would be more limiting at this time when the coronal magnetic field is very complex. In the future we will be able to perform higher resolution calculations on massively parallel computers. Finally, measurements of the transverse magnetic field in the photosphere may be important to get a more accurate estimate of the magnetic field in the corona. This may especially affect the non-radial inclination of streamers seen in the eclipse images above. Note that an effort is under way at the National Solar Observatory at Kitt Peak (the SOLIS Project) to measure the transverse magnetic field. When this data becomes available, we will be able to incorporate it into our model.
The photospheric magnetic field maps we use for our calculations are built up from daily observations of the Sun during a solar rotation. These maps give a good approximation of the Sun's magnetic flux if the large-scale flux is not changing much throughout a rotation. Previously, we have computed coronal models for an eclipse during the declining phase of the last solar cycle (November 3, 1994), for two eclipses during solar minimum (October 24, 1995, and March 9, 1997), and one eclipse during the the early rising phase of the new solar cycle (February 26, 1998). The August 11, 1999 eclipse, which occurs as we begin to approach solar maximum, presents new challenges. The photospheric magnetic field is evolving more rapidly now, making synoptic magnetic field data a less reliable approximation to the true state of the photospheric magnetic field. The increased complexity of coronal structures also requires higher resolution runs (~2,000,000 grid points) than in our previous computations (~650,000 grid points).
CR1949 (May 1 - May 28, 1999)
CR1950 (May 28 - June 24, 1999)
CR1951 (June 24 - July 21, 1999)
CR1952 (July 21 - August 18, 1999)
Photospheric magnetic field maps for four Carrington rotations leading up to the eclipse, CR1949, CR1950, CR1951, and CR1952, as measured by the National Solar Observatory at Kitt Peak. The maps show the measured photospheric field as a function of latitude (vertical axis) and Carrington longitude (horizontal axis). Red shows outward directed magnetic flux, and blue shows inward directed flux. Click the images for higher resolution pictures. These maps are considerably more complex than maps during solar minimum.
If your movie player can continuously loop a movie while
playing it, set this option to "on" for the best effect. For example, on
a Silicon Graphics machine, you would use the execute line:
movieplayer -l 0 cr1951.mpg
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