The August 1, 2008 Total Solar Eclipse
On Friday, August 1, 2008, a solar eclipse was visible in the northern hemisphere. A total eclipse occurred within a narrow corridor starting over northern Canada, in the north polar region, and in northern Russia, western Mongolia, and China. It was visible first near Cambridge Bay, Canada at sunrise (about 9:15 UT) and continued through Greenland, crossed the Arctic Ocean, entered Russia at 10:00 UT, and terminated between Xi’an and Nanjing, China at sunset (about 11:20 UT). Maximum eclipse occurred near Nadym, in northern Siberia, north of Novosibirsk, at 10:21 UT (17:21 local time), lasting 2 minutes and 27 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 17, 2008, 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 measured up to July 6, 2008, 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 22, 2008. This preliminary prediction can be found here. On July 23, 2008 we started a new calculation with updated magnetic field data that was measured with MDI up to July 21, 2008. This page has the updated (and final) prediction, which was posted on July 27, 2008.
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, 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.
Some technical details about the calculation that was used to make our final prediction can be found here.
Predicted polarization brightness (pB) in the solar corona for the eclipse expected on August 1, 2008 at 10:21 UT (corresponding to totality near Novosibirsk in Russia). 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 (left) together with traces of the magnetic field lines in the solar corona (right) for the eclipse expected on August 1, 2008 at 10:21 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 August 1, 2008 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 eclipses near solar minimum on November 3, 1994, October 24, 1995, March 29, 2006, and March 9, 1997.
CR2069 (Apr 16 – May 13, 2008)
CR2070 (May 13 – Jun 9, 2008)
CR2071 (Jun 9 – Jul 6, 2008)
CR2071+CR2072 (Jun 25 – Jul 21, 2008)
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) 2071 in our calculation for our preliminary eclipse prediction, which was posted on July 22, 2008. 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 operational) 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 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
Acknowledgements
Our work is supported by NASA’s Heliophysics Theory Program (HTP), Supporting Research & Technology (SR&T) Program, and Living With a Star (LWS) Program, by the Center for Integrated Space Weather Modeling (an NSF Science & Technology Center), and by AFOSR’s Space Sciences 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, where we performed our coronal prediction. We also thank the San Diego Supercomputer Center (SDSC) for an allocation on their DataStar supercomputer and NASA’s Advanced Supercomputing Division (NAS) for an allocation on the Columbia supercomputer, on which we have developed our code. We thank Yang Liu and Todd Hoeksema of the Solar Physics Group at Stanford University for providing us with timely access to MDI magnetograph data and for sharing their latest calibrated data with us.
Archived prediction, converted from the original 2008 page. Movies originally offered as GIF/WMV/QuickTime downloads are embedded above.
