The July 22, 2009 Total Solar Eclipse

On Wednesday, July 22, 2009, a solar eclipse was visible in the equatorial regions spanning both hemispheres. A total eclipse occurred within a narrow corridor in eastern Asia and the Pacific Ocean. It was visible first on the northwestern coast of India at sunrise (just before 01:00 UT) and continued through Nepal, Bangladesh, and Bhutan, crossing into China, where it was visible in several large cities, including Shanghai. The Moon’s shadow then crossed 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 occurred in the Pacific Ocean at 02:35 UT, lasting 6 minutes and 39 seconds. For a detailed description of the eclipse path, see NASA’s Eclipse page. For useful information about eclipse photography, see 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 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 has the updated (and final) prediction, which 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.

Some technical details about the calculation that was used to make our final prediction can be found here. You can also see the milestones in achieving our prediction.

Predicted polarization brightness, terrestrial north up — 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. Views aligned with solar north are on the original solar-north page.

Predicted polarization brightness with photospheric field contours — Predicted polarization brightness (left) together with traces of the magnetic field lines in the solar corona (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).

Traces of the magnetic field lines with photospheric field contours — Predicted polarization brightness (left) together with traces of the magnetic field lines in the solar corona (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).

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 29, 2006, and March 9, 1997), one eclipse during 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 occurred 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 previous August’s eclipse, and eclipses near solar minimum on November 3, 1994, October 24, 1995, March 29, 2006, and March 9, 1997.

Photospheric magnetic field map for CR2083 — 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) 2084 in our calculation for our preliminary eclipse prediction, which was posted on July 13, 2009. The last panel shows the magnetic field data that was used for the final eclipse prediction, which is shown on this page. 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.

Photospheric magnetic field map for CR2084 — 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) 2084 in our calculation for our preliminary eclipse prediction, which was posted on July 13, 2009. The last panel shows the magnetic field data that was used for the final eclipse prediction, which is shown on this page. 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.

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

Our 3D MHD model with improved energy transport allows us to simulate the emission from the corona in extreme ultraviolet and X-ray wavelengths. The Sun can be observed in these wavelengths from space. In particular, the SOHO/EIT, TRACE, STEREO/EUVI, and Hinode/EIS telescopes routinely take EUV images of the solar corona, and the Yohkoh/SXT (no longer operating) and Hinode/XRT telescopes image the soft X-ray Sun. Our simulated coronal emission is available on the original emission page.

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. The left movie shows pB in grayscale with a black disk occulting the Sun; the right shows pB with a blue background.

Polarization Brightness(grayscale)

Polarization Brightness(blue background)

Movie of Magnetic Field Lines

We have made a movie of the magnetic field lines and simulated emission from the Hinode XRT telescope (Al mesh filter). This is a simulated “synoptic” XRT image wrapped on the sphere, so emission on the limbs is not visible. Blue field lines are closed, green field lines are open. This movie illustrates the relationship of closed and open structures to features in emission.

Field Lines and Hinode XRT Emission

Publications

For technical details about our model, please see the following 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).
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 (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 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
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

Acknowledgements

Our work is supported by NASA, AFOSR, and NSF through the Strategic Capabilities program, by NASA’s Heliophysics Theory Program (HTP), by the Center for Integrated Space Weather Modeling (an NSF Science & Technology Center), by NASA’s Supporting Research & Technology (SR&T) Program, and by NASA’s Living With a Star (LWS) Program. We thank the staff at the Texas Advanced Computing Center (TACC) for graciously providing us with dedicated time on their massively parallel supercomputer Ranger, and NASA’s Advanced Supercomputing Division (NAS) for an allocation on the Pleiades supercomputer. Our calculations for the eclipse prediction were performed on these computers. We thank Todd Hoeksema of the Solar Physics Group at Stanford University for providing us with timely access to MDI magnetograph data and for sharing the latest calibrated data with us.

Archived prediction, converted from the original 2009 page. Movies originally offered as GIF/QuickTime downloads are embedded above.