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Predicting the Structure of the Solar Corona During the August 21, 2017 Total Solar Eclipse |
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On August 21, 2017, a total eclipse of the Sun will be visible across the entire contiguous United States. It will trace out a band, approximately 70 miles wide across fourteen states, being first visible shortly after 10:15am PDT at Oregon's Pacific coast, and finally finishing in Charleston, South Carolina. The longest duration of totality will be 2 minutes and 42 seconds, which will occur in Giant City State Park, near Carbondale, Illinois. A partial eclipse will be visible across a much broader band including all of North America, northern South America, Westren Europe, and even parts of Africa. To see an interactive map of the path of the eclipse, please visit Xavier Jubier's 2017 total eclipse interactive Google map. For general information about eclipse photography, please visit Fred Espenak's Eclipse web site.
On July 28, 2017, we started an MHD computation of the solar corona, in preparation for our prediction of what the solar corona will look like during this eclipse. We used data measured by the HMI magnetograph aboard NASA's SDO spacecraft. We used a combination of HMI synoptic maps, including data for Carrington rotation 2192 combined with data from a part of Carrington rotation 2193 measured up to 12:00 UTC on July 26, 2017.
This preliminary prediction of the state of the solar corona during the eclipse was posted on July 31, 2017. We intend to update this prediction on August 16, 2017 with updated magnetic field data.
Our prediction is based on a magnetohydrodynamic model of the solar corona. While our earlier predictions incorporated more simplistic heating formalism, for the first time, here, we have applied a wave-turbulence-driven (WTD) methodology for heating closed coronal loops. This, we believe, better reproduces the underlying physical processes in the corona, and will result in a more accurate eclipse prediction. Additionally, these simulations are the largest we have performed, using 65 million grid points. For technical details about our model, please see the publications below. The prediction shown here also allows us to predict emission in extreme ultraviolet (EUV) wavelengths and X-rays. The EUV emission can be compared with solar observations from the EIT imager on SOHO, and the AIA instrument on SDO. X-ray emission can be compared with solar observations from the XRT instrument on Hinode. We also predict the scattering of polarized white light (polarization brightness, pB) that is typically measured during an eclipse. Movies of our simulated polarization brightness can be found below.
You can read the technical details about the calculations that were used to make our predictions.
The images above show our preliminary prediction of the polarization brightness (pB) and the magnetic field lines in the solar corona for the eclipse expected on August 21, 2017 at 17:18 UTC (corresponding to the time of peak eclipse near Salem, Oregon, which occurs at 10:18 local time). 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. The Sun's surface shows color contours of the radial component of the measured photospheric magnetic field from the HMI magnetograph, showing the location of active regions (strong magnetic fields). To view these image in a coordinate system aligned with solar north, click here. Click on the images to see larger versions.
Our 3D wave-turbulent-driven MHD model 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, STEREO/EUVI,
and Hinode/EIS telescopes routinely take EUV images of the solar corona, and the Hinode/XRT telescope images the soft X-ray Sun.
Our simulated coronal emission is available here.
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 selection of our movies here.
Additional grayscale movies of pB with a black disk occulting the Sun can be downloaded: (1) a
GIF version
(20 Mbytes, recommended); (2) a
QuickTime version
(22 Mbytes); or (3) a half-resolution
GIF version
(6 Mbytes).
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). Download PDF
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). Download PDF
Lionello, R., Velli, M., Downs, C., Linker, J.A., Mikić, Z. and Verdini, A., "Validating a time-dependent turbulence-driven model of the solar wind," Astrophys. J., 784(2), p.120 (2014). Download PDF
Downs, C., Lionello, R., Mikić, Z., Linker, J. A., & Velli, M., "Closed-field Coronal Heating Driven by Wave Turbulence," Astrophys. J., 832(2), 180. Chicago, (2016). Download PDF
NASA's Eclipse web site
Our work is supported by NASA (Heliophysics Grand Challenges Research, Heliophysics Supporting Research, and Living with a Star programs), AFOSR, and NSF. We are grateful to NASA's Advanced Supercomputing Division (NAS) for an allocation on the Pleiades supercomputer, and the Texas Advanced Computing Center (TACC) for an allocation on the Stampede supercomputer, which allowed us to complete the eclipse prediction simulations shown here. We also thank the SDO/HMI team of the Solar Physics Group at Stanford University for their support in providing timely access to HMI Synoptic magnetograph data.
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