During the March 29, 2006 Total Solar Eclipse
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Predicting
the Structure
of the Solar Corona During the March 29, 2006 Total Solar Eclipse |
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On Wednesday, March 29, 2006, a solar eclipse was visible in the northern hemisphere. A total eclipse occurred within a narrow corridor starting near the equator in the Atlantic ocean, crossed central and northern Africa, went across the Mediterranean sea to Turkey and terminated at sunset in central Asia. Maximum eclipse occurred in the southern desert of Libya, lasting 4 minutes and 7 seconds. The eclipse was visible in Egypt near the Libyan border at 10:40 UT (12:40 local time) with a duration of 3 min. 58 sec., and near Antalya in Turkey at 10:57UT (13:57 local time) with a duration of 3 min. 45 sec. To see a detailed description of the eclipse path, please visit NASA's Eclipse page. For useful information about eclipse photography, please visit Fred Espenak's Eclipse web site.
On 12 March, 2006, we initiated an
MHD
computation of the solar corona, in preparation for our prediction
of what the solar corona would look like during this eclipse. We used
photospheric magnetic field data measured up to March 10, 2006, by the MDI magnetograph aboard the SOHO spacecraft. We
typically also use magnetic field measurements from the Wilcox Solar Observatory
at Stanford and the National Solar Observatory SOLIS vector magnetograph at Kitt
Peak. A very useful prediction
of the photospheric solar magnetic field is carried out by Karel
Schrijver and Marc DeRosa at Lockheed
Martin.
A preliminary prediction of the state of the solar corona during the
eclipse based on this data was published on this web site. This
preliminary prediction can be found here.
On March 18, 2006 we started a new calculation with
updated magnetic field data that was measured with MDI up to March 17,
2006.
This page now has the updated (and final) prediction, and was posted on
March
24, 2006.
This year we have significantly improved our coronal modeling
capability. In the past we have used the "polytropic" model to
describe the flow of energy in the corona. This is a crude model
of the corona that greatly simplifies the calculations. In recent
years we have improved the energy equation in our model to include the
effects of coronal heating, the conduction of heat parallel to the
magnetic field lines, radiative losses, and the effect of Alfvén
waves. This produces a significantly better estimate of the
plasma temperature and density in the corona. For technical
details about our improved model, please see the publications
below. The prediction shown here uses our new model, and allows
us to predict emission in extreme ultraviolet (EUV) wavelengths and
X-rays, which can be compared with solar observations from the EIT imager on SOHO and the X-ray
instrument on Yohkoh
(no longer operational), in addition to emission in polarized white
light (polarization
brightness, pB) that is typically measured during an eclipse.
For a comparison between our predicition and several eclipse
observations, please go here.
A publication describing these results is available below.
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The figure on the left shows the predicted polarization brightness (pB) in the solar corona for the eclipse expected on 29 March, 2006 at 10:57UT (corresponding to totality near Antalya, Turkey). The state of the solar corona was computed using a 3D magnetohydrodynamic (MHD) simulation. The pB signal is produced by white light scattered off electrons in the coronal plasma. The image has been radially detrended using the Newkirk vignetting function 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. |
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| Predicted polarization brightness (top left) together with traces of the magnetic field lines in the solar corona (top right) for the eclipse expected on March 29th, 2006 at 10:57UT (with terrestrial north up). The Sun's surface shows color contours of the radial component of the measured photospheric magnetic field from the MDI magnetograph, showing the location of active regions (strong magnetic fields). Click the images for higher resolution pictures. To view these images in a coordinate system aligned with solar north, click here. |
| 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), one eclipse during the the early rising phase of solar
cycle
23 (February
26, 1998), one eclipse approaching solar maximum (August
11, 1999), and two eclipses near solar maximum (June 21, 2001 and December 4, 2002). The March 29, 2006 eclipse occurs near solar minimum, so the solar corona ought to (and does) have a simpler structure than at solar maximum. It can be seen that the solar corona is most similar to that seen in the eclipses near solar minimum on November 3, 1994, October 24, 1995, and March 9, 1997. These figures show the evolution of the solar photospheric magnetic field for three Carrington rotations preceding the eclipse, as measured by the SOLIS vector magnetograph at the National Solar Observatory at Kitt Peak, and one rotation from the MDI magnetograph aboard the SOHO spacecraft. This last rotation, which contains data measured from Feb. 18 through March 17, 2006, and includes parts of Carrington rotations 2040 and 2041, was the data used in our calculation for the updated eclipse prediction; this calculation was started on March 18. The maps show the measured photospheric magnetic 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. |
CR2038 (Dec 22, 2005 – Jan 18, 2006) CR2039 (Jan 18 – Feb 15, 2006) CR2040+CR2041 (Feb 18 – Mar 17, 2006) |
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Z. Mikic, J. A. Linker, D. D. Schnack, R. Lionello, and A. Tarditi, "Magnetohydrodynamic Modeling of the Global Solar Corona," Physics of Plasmas, 6, 2217 (1999). Access Article
Z. Mikic, J. A. Linker, P. Riley, and R. Lionello, "Predicting the Structure of the Solar Corona During the 11 August 1999 Total Solar Eclipse," in The Last Total Solar Eclipse of the Millennium, Proceedings of the Conference held in Istanbul, Turkey, 13-15 August, 1999 (W. Livingston and A. Ozguc, eds.), ASP Conference Series, Vol. 205, p. 162 (2000). Download PDF
Z. Mikic, J. A. Linker, R. Lionello, P. Riley, and V. Titov, "Predicting the Structure of the Solar Corona for the Total Solar Eclipse of March 29, 2006," in Solar and Stellar Physics Through Eclipses (O. Demircan, S. O. Selam, and B. Albayrak, eds.), ASP Conference Series, Vol. 370, p. 299 (2007). Access Article
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