HT Bureau
GUWAHATI, June 15: A recent study has discovered that the bright particles observed in the Sun’s chromosphere are caused by upward-moving shockwaves in the solar plasma. These shockwaves exhibit higher temperature increases than previously estimated, providing valuable insights into the heating mechanism of the chromosphere, located between the Sun’s bright surface and the extremely hot corona.
The chromosphere is a dynamic layer within the Sun’s atmosphere that plays a crucial role in transferring non-thermal energy, which heats the corona and fuels the solar wind extending into the surrounding regions of the solar atmosphere. While a significant portion of this energy is converted into heat and radiation, only a small fraction is utilized to heat the corona and power the solar wind.
Currently, there are two widely accepted mechanisms for transmitting energy from the lower layers to the higher regions of the solar atmosphere. The first mechanism involves the rearrangement of magnetic field lines, transitioning from higher to lower potential. The second mechanism involves the propagation of various types of waves, including acoustic waves.
Acoustic shockwaves are heating events in the chromosphere that manifest as transient brightenings, known as grains, in images. Understanding the energy carried by these acoustic waves and how they heat the chromosphere is of great interest in solar and plasma astrophysics.
A team of solar physicists from the Indian Institute of Astrophysics (IIA), in collaboration with researchers from Norway and the USA, led a study to quantify the temperature enhancements observed during these acoustic shock events. By utilizing data with the highest imaging, wavelength, and temporal resolution to date, the scientists found that, on average, the temperature increase during these events can reach approximately 1100 K, with a maximum of around 4500 K. These values are three times higher than previous estimates. Additionally, they discovered that the atmospheric layers displaying temperature enhancement predominantly move in an upward direction.
To infer the atmospheric properties during acoustic shocks, the team employed high-quality observations from the Swedish Solar Telescope and a sophisticated inversion code called STiC, which was run on a supercomputer provided by the IIA. Machine learning techniques were also utilized to optimize the inversion process, significantly accelerating computation.
“The processes by which energy from the Sun’s interior is transported to the chromosphere and corona still puzzle scientists,” stated Harsh Mathur, a PhD student at IIA and the lead author of the study. He added, “We have been able to determine the temperature enhancements and plasma motion during acoustic shocks. These shocks, caused by sound waves originating from lower altitudes, can heat the chromosphere.” Nagaraju from IIA, a co-author of the study, explained, “These shockwaves increase the plasma density in the chromosphere, resulting in distinct brightening, referred to as grains, in the observations used to identify such events in this study.”
Jayant Joshi of IIA, the principal investigator of the study, elaborated, “The temperature enhancements calculated in this study are 3-5 times greater than previous estimates. Our findings support earlier studies’ interpretation that these temperature enhancements are caused by upflowing plasma.”
The research team includes Harsh Mathur and K Nagaraju from IIA in Bengaluru, India, along with Jayant Joshi. The international team comprises Prof Luc Rouppe van der Voort from the University of Oslo and Dr Souvik Bose from the Lockheed Marin Solar & Astrophysics Laboratory in the USA.
