Predicting the Structure of the Solar Corona During the July 11, 2010 Total Solar Eclipse

On Sunday, July 11, 2010, a total eclipse of the Sun will be visible in the southern hemisphere. A total eclipse will follow a path through the South Pacific Ocean crossing only the Cook islands and Easter Island. A partial eclipse will be visible over a much larger path, including the southern portion of South America. The eclipse will begin at 18:15UT, when the Moon's shadow first touches the Earth. The track will be 179km wide, and totality will last initially for 2 min 42 sec along the central line. By the time it reaches the Cook Islands, totality will last for 3 min 18 sec. The Easter Islands will enjoy 4 min 41 sec of totality. Totality finally ends 2 hours and 39 minutes later as the shadow crosses the Andes, into Argentina. To see a detailed description of the eclipse path, please visit NASA's Eclipse page, or useful information about eclipse photography, please visit Fred Espenak's Eclipse web site. Detailed information concerning all eclipses occurring in 2010 can be found in this PDF document.

On July 2nd, 2010, 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 2097, measured up to June 16, 2010, using the MDI magnetograph aboard the SOHO spacecraft. We typically also use magnetic field measurements from the Wilcox Solar Observatory at Stanford University 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 5, 2010.  (This prediction was updated slightly on July 6 to correct an error in the solar viewing parameters for the moment of greatest eclipse.)  This preliminary prediction can be found here.   On July 6, 2010 we started a new calculation with updated magnetic field data that was measured with MDI up to July 3, 2010. This page now has the updated (and final) prediction, and was posted on July 8, 2010.

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. Since then, we have predicted a number of other total eclipses. 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 Alfven 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. Movies of our simulated polarization brightness can be found below.

If you are curious, you can see the milestones in achieving our prediction here.

The figure on the left shows the predicted polarization brightness (pB) in the solar corona for the eclipse expected on July 11, 2010 at 19:33 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.

Evolution of the Photospheric Magnetic Field

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 9, 1997, March 29, 2006, August 1, 2008, and July 22, 2009), 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 11, 2010 eclipse occurs during the rising phase of solar cycle 24, so the solar corona has a more complex structure than at solar minimum.

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.

We used the data for Carrington rotation (CR) 2097 in our calculation for our preliminary eclipse prediction, which was posted on our web site on July 5, 2010, and can be found here.  The last panel shows the magnetic field data that was used for the final eclipse prediction, which is posted on this page.  That calculation was started on July 6, 2010, and was posted on our web site on July 8, 2010.

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.

CR2096 (April 22 – May 19, 2010)

CR2097 (May 19 – June 16, 2010)

CR2097+CR2098 (June 6 – July 3, 2010)

Images and Movies of Coronal Emission in EUV and X-Rays

Movies of Polarization Brightness

We have made movies of the polarization brightness (pB) from our MHD simulation.  This illustrates visually how the solar corona changes as a result of solar rotation. You can see a grayscale movie of pB with a black disk occulting the Sun: a GIF version (3.7 Mbytes, recommended), a QuickTime version (1.8 Mbytes), or a half-resolution GIF version (1.3 Mbytes). You can also see a movie of pB with a blue background and a black disk occulting the Sun: a GIF version (3.7 Mbytes, recommended), or a QuickTime version (3.6 Mbytes).

If your movie player can continuously loop a movie while playing it, set this option to "on" for the best effect. 

Movies of Magnetic Field Lines

Publications

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).   Download PDF

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).   Download PDF

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

Other web resources for the eclipse

• NASA's Eclipse web site (A great resource for the eclipse, including lots of information).
• MrEclipse.com

Acknowledgments