During the July 22, 2009 Total Solar Eclipse
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Predicting
the Structure
of the Solar Corona During the July 22, 2009 Total Solar Eclipse |
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On Wednesday, July 22, 2009, a solar eclipse will be visible in the equatorial regions spanning both hemispheres. A total eclipse will occur within a narrow corridor in eastern Asia and the Pacific Ocean. It will be visible first on the northwestern coast of India at sunrise (just before 01:00 UT) and continue through Nepal, Bangladesh, and Bhutan, crossing into China, where it will be visible in several large cities, including Shanghai. The moon's shadow will then cross into the East China Sea, across Japan’s Ryukyu Islands, and on to Iwo Jima at 02:27 UT, the Marshall Islands, and the Gilbert Islands, ending in the southern Pacific Ocean at 04:18 UT. Maximum eclipse will occur in the Pacific Ocean at 02:35 UT, lasting 6 minutes and 39 seconds. 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 July 9, 2009, we started 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 for Carrington rotation 2084, measured
up to June 26, 2009 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 posted on this web site on July 13,
2009.
This
preliminary prediction can be found here.
On July 15, 2009 we started a new calculation with
updated magnetic field data that was measured with MDI up to July 11,
2009.
This page now has the updated (and final) prediction, and was posted on
July 19, 2009.
Our prediction is based on a magnetohydrodynamic model of the solar
corona with improved energy transport. We used this model for the
first time to predict the structure of the corona prior to the March 29, 2006 total solar
eclipse. The improved energy equation model includes 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 Hinode,
in
addition to emission in
polarized white
light (polarization
brightness, pB) that is typically measured during an eclipse.
Some technical details about the calculation that was used to make our
final prediction can be found here.
For your curiosity, you can see the milestones in achieving our
prediction here.
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The figure on the left shows the predicted polarization brightness (pB) in the solar corona for the eclipse expected on July 22, 2009 at 02:35 UT (corresponding to the moment of greatest eclipse in the Pacific Ocean). 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 greater 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 July 22, 2009 at 02:35 UT (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 does not change 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
three eclipses during solar minimum (October 24, 1995, March 29, 2006, 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 July 22, 2009 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 last August's eclipse, and eclipses near solar minimum on November 3, 1994, October 24, 1995, March 29, 2006, and March 9, 1997. These figures show the evolution of the radial component (Br)
of the solar photospheric
magnetic field for three Carrington
rotations preceding the eclipse, as measured by the MDI
magnetograph aboard the SOHO spacecraft. We use smoothed
versions of these magnetic field maps in our calculations. These maps show the radial component of the magnetic field deduced from the measured photospheric field as a function of latitude (vertical axis) and Carrington longitude (horizontal axis). Red shows outward directed magnetic field, and blue shows inward directed field. The dark regions near the top and bottom indicate areas near the solar poles where it is not possible to estimate the radial component of the magnetic field due to projection effects. Click the images for higher resolution pictures. |
CR2084 (May 30 – June 26, 2009) CR2084+CR2085 (June 14 – July 11, 2009) |
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Z. Mikić, 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. Mikić, 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. Mikić, J. A. Linker, R. Lionello, P. Riley, and V. Titov, "Predicting the Structure of the Solar Corona for the Total Solar Eclipse of August 1, 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
R. Lionello, J. A. Linker, and Z. Mikić, "Multispectral Emission of the Sun During the First Whole Sun Month: Magnetohydrodynamic Simulations," Astrophys. J., , 690, 902 (2009). Access Article
V. Rušin, M. Druckmüller, P. Aniol, M. Minarovjech, M. Saniga, Z. Mikić, J. A. Linker, R. Lionello, P. Riley, and V. S. Titov, "Comparing Eclipse Observations of the 2008 August 1 Solar Corona with an MHD Model Prediction," Astron. Astrophys., 513, A45 (2010). Access Article
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