Sunday, February 12, 2017

ALMA to Reveal New Insights into the Solar Chromosphere

ALMA observes the full solar disc. Credit: ALMA (ESO/NAOJ/NRAO)

The Atacama Large Millimeter/submillimeter Array (ALMA) in Chile could soon become one of the most important ground-based observatories to observe the Sun. The facility has recently commenced the observation of solar activity at longer wavelengths of light than usually available, what could improve our understanding of the solar chromosphere – the region which forms the visible surface of the Sun.

“ALMA observations of the Sun are extremely important because ALMA enables us to study the Sun in a new frequency region with high spatial, temporal and spectral resolution,” Ivica Skokic of the Czech ALMA Regional Center Node told

In order to better understand the processes taking place in the solar chromosphere, it is necessary to study the Sun across the entire electromagnetic spectrum, including the millimeter and millimeter portion. ALMA has such capabilities to image the millimetre-wavelength light emitted by the solar chromosphere.

Due to the forming mechanism of radiation that ALMA detects, it can be approximately used as a linear thermometer. This radiation originates in the chromosphere, a layer which transports energy and matter from photosphere to corona.

“All of this enables us to study the solar chromosphere and its dynamics in high detail, find new clues to the problem of coronal heating, test and improve our models so we better understand the Sun and predict its behavior more accurately,” Skokic said.

Recently, a team of researchers, including Skokic, has observed an enormous sunspot at wavelengths of 1.25 millimeters and 3 millimeters using two of ALMA's receiver bands. The images reveal differences in temperature in the solar chromosphere. Further ALMA observations could reveal detailed temperature and magnetic structure of sunspots and prominences, temporal evolution of flares and probe the underlying drivers of coronal mass ejections (CMEs).

“With ALMA, it will be possible to study these mechanisms in a new light,” Skokic told

Regular ALMA observations of the Sun already started in December 2016 and will continue in the future as the interest from the solar physics community is very high. Skokic noted that ALMA was designed to support solar observations and is now being upgraded and improved constantly to enable more detailed studies of the Sun.

“For solar observations the plan is to go to even higher spatial, temporal and spectral resolution, to enable circular polarization and (near)-simultaneous multi-band measurements, which will give us information on magnetic fields and temperature variation with height in the chromosphere,” Skokic concluded.

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