New Paper Discusses Abundance of Helium Relative to Hydrogen in the Solar Corona

The paper, "Global Helium Abundance Measurements in the Solar Corona," was published online in Nature Astronomy.

New Paper Published by NRL Scientists

By Paul Cage

U.S. Naval Research Laboratory Corporate Communications

Two U.S. Naval Research Laboratory Space Science Division (SSD) researchers joined an international cadre of scientists on July 27, 2020, in presenting the results of the first simultaneous global solar corona images of the helium and hydrogen emission that is helping scientists to better understand the space environment.

Image Attribute: A composite image of the Sun showing the hydrogen (left) and helium (center and right) in the low corona. The helium at depletion near the equatorial regions is evident. / Courtesy NASA

The paper, "Global Helium Abundance Measurements in the Solar Corona," was published online in Nature Astronomy and discusses the abundance of helium relative to hydrogen in the solar corona, the outer atmosphere of the sun, seen from the earth only during eclipses.

NRL Astrophysicist Dennis Wang, Ph.D., software lead for the HElium Resonance Scattering in the Corona and HEliosphere (HERSCHEL) rocket flight, was responsible for flight and ground software. His NRL colleague, Research Physicist Martin Laming, Ph.D., managed the new model of element abundance fractionation, to include helium.

"Understanding space weather is important for space situational awareness, that is, forecasting and mitigating the effects of solar activity on Navy and Defense Department satellites," said Laming. "This was one case where instead of explaining the observations after the fact, I was able to see a prediction I had made come true."

The HERSCHEL sounding rocket, launched on September 14, 2009, provided a number of technological advances in space-based remote sensing. Using a concept developed at NRL for a coronagraph functioning in the extreme ultraviolet regime of the electromagnetic spectrum, the helium coronagraph obtained the first images of the solar atmosphere in the region of the solar wind source surface from light resonantly scattered from helium ions.

The leading model for solar wind variability used by the Department of Defense and National Oceanic and Atmospheric Administration space weather forecasters is an NRL SSD product, known as the Wang, Sheely, Arge Model which is based on simple assumptions about the relation of the solar magnetic field structure and the solar wind and is reasonably successful in predicting the overall variability of the solar wind as it reaches Earth.

Geomagnetic storms impact radio frequency transmission at frequencies refracted or reflected, by the ionosphere. The Navy uses magnetic sensors in various battlespace applications, which could be disrupted during large geomagnetic storms and Coronal Mass Ejections. These are major reasons why the Navy is interested in disruptions of the Earth's magnetic field structure in these measurements.

"There is a long chain of work efforts that go from a fundamental understanding of the solar atmosphere to specifying the observables that need to be monitored before we eventually get to reliable Space Weather forecasts," said Laming. "In the future, service members should anticipate more reliable satellite-based Command, Control, Communications, Computers, Intelligence, Surveillance, and Reconnaissance."

Laming demonstrates a strong belief in his model's prediction capability and his understanding of the sun's corona adding, "I think we all have more confidence in my model and the conclusions one might draw from it."

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