New Study Reveals Detailed Structure of the Sun’s Tacocline Layer

New Research Offers Unprecedented View of the Sun’s Interior

An international team led by Dr. Sylvain G. Korzennik of the Harvard-Smithsonian Center for Astrophysics and Dr. Antonio Eff-Darwich Peña of the University of La Laguna and the Institute of Astrophysics of the Canary Islands has published a study detailing a new understanding of the Sun’s internal structure. The research, published in The Astrophysical Journal, utilizes over 25 years of continuous helioseismic observations to analyze the deepest layers of the Sun.

Helioseismology studies the patterns of oscillation on the solar surface over time. Like any musical instrument, the characteristics of these vibrations depend on the physical properties of the Sun’s interior. The study specifically focuses on the solar tachocline, a thin layer approximately 200,000 kilometers beneath the solar surface, where temperatures reach around two million degrees Celsius. This layer marks a transition between distinct rotational regimes and is key to understanding fundamental processes like the generation of the solar magnetic field and the mechanisms driving the Sun’s activity cycle.

The research team characterized this transitional layer with unprecedented precision by analyzing data from three complementary instruments: the Global Oscillations Network Group (GONG), operated by the National Solar Observatory; the Michelson Doppler Imager (MDI) aboard the European Space Agency/NASA’s Solar and Heliospheric Observatory (SOHO) satellite; and the Helioseismic and Magnetic Imager (HMI) on NASA’s Solar Dynamics Observatory (SDO) satellite. According to the Harvard-Smithsonian Center for Astrophysics, Korzennik is a co-investigator on the HMI experiment.

Processing this vast amount of data required innovative numerical techniques specifically designed for the study, including simultaneous algebraic reconstruction and the implementation of computational grids with a higher-than-usual radial density. These methodologies improved the resolution of the results while controlling the amplification of observational noise, a critical aspect when studying subtle and deep structures like the tachocline.

“Still, it’s incredible to me that we can explore what’s happening hundreds of thousands of kilometers below the surface of the Sun, which is itself 150 million kilometers from Earth,” said Eff-Darwich.

Beyond its fundamental physics implications, research of this kind is essential for improving our understanding of space weather – the tracking of the impact of the Sun’s magnetic activity on Earth. The tachocline is closely linked to the processes responsible for solar magnetism, which, when emerging to the surface, can cause solar storms and coronal mass ejections that can affect our technological infrastructure.

The study suggests that the position of the tachocline exhibits a discontinuity between low and high latitudes, revealing a more complex internal structure than previously assumed. The results also indicate that this layer could be extremely thin, possibly less than one percent of the solar radius.

The research also explores potential temporal variations and concludes that, while the available data does not yet allow for the definitive detection of changes associated with solar activity, continued development of these analytical tools is necessary to deepen our understanding of the Sun’s internal dynamics and improve our ability to anticipate the effects of solar activity on Earth. “This new measurement will further confound theorists and modelers as they attempt to explain why the tachocline is the way it is,” Korzennik stated.