PRELIMINARY OBSERVATIONAL RESULTS

Figure 1. Image on the left whows the LASCO C2 observation overlaid on the predicted large scale coronal magnetic field lines. The right mimics the expected brightness image created utilizing various filters.

We compare the simulation results with the images acquired on the day of the eclipse of 26 December 2019, through a space based coronagraph (SOHO/ LASCO C2) which observes upto 6 solar radius. The bright streamers (seen in LASCO C2) beyond the source surface (marked in white background) tend to orient along the closed magnetic loops. The observations show a very good match with the predicted tilt of the extended plumes which carry high-speed solar wind particles into interplanetary medium. The image on the right show the predicted synthetic coronal brightness for the eclipse on 26 December 2019. Further analysis with observations from MLSO K-Cor data might tell us more about the near-sun magnetic topology.

Figure 2. Prediction of the Sun's coronal magnetic field structure (solar north up).
We predict two large-scale petal-like structures (known as helmet streamers) on each limb (side) of the Sun on the day of the eclipse. These petal-like streamers consist of closed magnetic loops that connect opposite magnetic polarities on the Sun's surface. Both the streamers would be cross-equatorial. The streamer on the right (west) limb of the Sun would be centered just south of the equator, and the streamer on the left (east) limb would be centered just north of the equator. Both the edges of the streamer on the left limb would be smoothed out by emission from closed magnetic field lines that lie adjacent to these edges. Open magnetic field lines dominate the Sun's north and south poles which is expected at this time nearing the minimum activity level between two solar maxima. A plausible pseudo-streamer like elongated structure exists in the north-west limb at mid latitudes. In large-angle coronagraph images acquired during the eclipse, bright extended plumes beyond the source surface (dashed circle in the above figure) are expected to be aligned with the outward radial line connecting the Sun center to the tips or cusps of the predicted streamers.

Figure 3. Prediction of Sun's synthetic "white-light" coronal structure (solar north up) with the solar disk completely occulted.
As this is a partial eclipse, observing the lower solar corona is difficult without artificially occulting the solar disk. Space and ground based coronagraphs e.g. SOHO/LASCO, MLSO-K coronagraph will be recording the solar corona in white-light. The predicted synthetic white-light image is what is expected to be seen if we use a coronagraph (which blocks the disk of the Sun completely).

Figure 4. Prediction of Sun's synthetic "white-light" coronal structure (solar north up) with part of the outer solar disk visible as an annular ring.
The view in Figure 4 is expected to be seen during the annular eclipse. However because the outer annulus would be extremely bright, the extended coronal structures would not be visible without an occulter.

HOW DO WE MAKE THE PREDICTION

Novel utilization of two disparate computational models based on a theoretical framework postulated in Nandy et al. (2018) allows long-term prediction of the Sun's coronal magnetic field structure. The Predictive Solar Surface Flux Transport (PSSFT) model developed at CESSI (Bhowmik & Nandy 2018) is forward run for 43 days (since the last observed active region emergence) to first predict the surface magnetic field distribution on the Sun's surface expected on 26 December 2019. Subsequently, a potential field source surface model utilizes the predicted solar surface field as its boundary condition to extrapolate the coronal fields expected on the day of the eclipse.

The synthetic white light corona is generated from the predicted coronal fields by assigning more weight to closed field lines relative to the open field lines, and utilizing a combination of filters to approximately capture the density stratification of the corona.

REFERENCES TO RELEVANT MANUSCRIPTS

  • "Prediction of the Sun's Corona for the Total Solar Eclipse on 2019 July 2", Dash S., Bhowmik P., Nandy D., RNAAS, 2019, Vol 3, Num 6, link
  • "The Large-scale Coronal Structure of the 2017 August 21 Great American Eclipse: An Assessment of Solar Surface Flux Transport Model Enabled Predictions and Observations", Nandy D., Bhowmik P., Yeates A. R., Panda S., Tarafder R., Dash S., The Astrophysical Journal, 2018, Vol 853, Num 1, link
  • "Prediction of the strength and timing of sunspot cycle 25 reveal decadal-scale space environmental conditions", Bhowmik P., Nandy D., Nature Communications, 2018, Vol 9, Num 5209, link

ACKNOWLEDGEMENTS

This eclipse prediction for 26 December 2019 has been conducted at CESSI – a multi-institutional Center of Excellence established at IISER Kolkata and funded by the Ministry of Human Resource Development, Government of India under the FAST scheme. We acknowledge funding from the DST-INSPIRE program. Many undergraduate and graduate students have contributed over the years to the development of the CESSI solar corona prediction methodology. They are:
  • Soumyaranjan Dash, PhD student at CESSI, IISER Kolkata
  • Prantika Bhowmik, PhD student at CESSI, IISER Kolkata (Now at Durham University)
  • Athira B S, PhD Student at CESSI, IISER Kolkata
  • Rajashik Tarafder, BS-MS student at CESSI/DPS, IISER Kolkata (Now at California Institute of Technology)
  • Suman Panda, BS-MS student at CESSI/DPS, IISER Kolkata (Now at Montana State University)

FOR TECHNICAL INFORMATION CONTACT

Dibyendu Nandi: dnandi @ iiserkol . ac . in

THE SOLAR ECLIPSE OF 26 DECEMBER 2019

An annular solar eclipse will occur on December 26, 2019. When the moon passes between the Earth and the Sun we see the Moon's shadow on Earth, which obstructs the Sun creating the phenomena of solar eclipse (for those who are within the Moon's shadow). An annular eclipse will occur on 26 December 2019. This eclipse would be annular because the apparent diameter of the Moon would be smaller than the Sun's diameter on the day of the eclipse. This partial eclipse will begin from Saudi Arabia and end in Guam. It will reach southern coast of India at 26 Dec 2019 09:26 AM IST (26 Dec 2019 03:56 UTC) and will last for about 8 minutes. For more information and resources on the eclipse, see https://astron-soc.in/outreach/.

SUGGESTED READING

  1. ISRO's Aditya L1 Mission
  2. Coronal Multi-channel Polarimeter (CoMP)
  3. Daniel K. Inouye Solar Telescope (DKIST)
  4. Website: The Great American Solar Eclipse
  5. Website: CESSI Prediction of South American Total Solar Eclipse 2019
  6. Website: http://eclipsewise.com/oh/ec2019.html
  7. Website: https://en.wikipedia.org/wiki/Solar_eclipse_of_December_26,_2019
  8. Website: https://www.history.com/news/how-5-ancient-cultures-explained-solar-eclipses
  9. Website: https://www.britannica.com/list/the-sun-was-eaten-6-ways-cultures-have-explained-eclipses
  10. Astronomical Society of India Outreach website: https://astron-soc.in/outreach/

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