Chuck Bednar for redOrbit.com – @BednarChuck
While the temperature of the Sun’s atmosphere can reach highs of more than one million degrees Celsius, its surface temperature is only about 6,000 degrees Celsius. Now a team of French astrophysicists has explained the mechanisms for this unusual phenomenon.
In research published last week in the journal Nature, Dr. Tahar Amari, the Director of Research at the French National Centre for Scientific Research (CNRS), and his colleagues simulated part of the evolution of the sun’s interior and exterior and discovered a layer beneath the surface of the Sun that provides sufficient energy to heat up the solar atmosphere.
This layer acts like a pan of boiling water and is believed to help generate a small-scale magnetic field that serves as an energy reserve. Once this field emerges from the star, it heats successive layers of the solar atmosphere through a series of branches and roots, contributing to the generation of the solar wind that fills the heliosphere.
At the sun’s core, temperatures can reach temperatures of about 15 million degrees Celsius, but it grows cooler further away from the center, falling to just 6,000 degrees at its surface. While it would seem logical that the temperatures would continue to decline in the atmosphere, surprisingly they increase to about 10,000 degrees in the chromosphere.
In-depth look at the mechanisms behind this phenomenon
By the time you reach the corona, those temperatures spike to more than one million degrees Celsius. To determine what type of energy source can heat the atmosphere to such consistently high temperatures, Dr. Amari and his colleagues created a model of the Sun’s heating in which magnetic fields were generated by a subphotospheric fluid dynamo linked to granulation.
“We find that the fields expand into the chromosphere, where plasma is heated at the rate required to match observations (4,500 watts per square meter) by small-scale eruptions that release magnetic energy and drive sonic motions,” they wrote. “Some energetic eruptions can even reach heights of 10 million meters above the surface of the Sun, thereby affecting the very low corona.”
Their simulations latest for several hours and were based on a model of the Sun in which there were multiple layers, including one in the Sun and several others in the atmosphere. They found that the thin layer beneath the surface acts like a boiling plasma soup that is heated from below, amplifying and maintaining the magnetic field largely responsible for this phenomenon.
Their calculations revealed that the atmospheric heating that begins in the chromosphere is the result of a series of micro-eruptions in a structure resembling the roots of a mangrove forest and carries intense electrical current along with bubbles emitted from the boiling plasma. This process generates magnetic waves that transport energy to the upper corona, where they are heated as a result of progressive dissipation, the researchers noted.
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