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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - SUNMAG (SUNMAG: Understanding magnetic-field-regulated heating and explosive events in the solar chromosphere)

Teaser

Summary

This project represents a new powerful approach to a fundamental problem in solar physics: the heating of the solar chromosphere. The aim of SUNMAG is to identify the mechanisms that heat the chromosphere and characterize the energy flux that is being released into the outer layers of the Sun in active regions and flares. By investigating how the chromosphere regulates the energy and mass transport we can also contribute to an understanding of the heating of the corona and the acceleration of the solar wind.

The problem of chromospheric and coronal heating remains one of the foremost open questions in astrophysics: how are the outer layers of the Sun heated from a few thousand to multi-million degrees. What are the physical processes responsible for energy transport and deposition? Chromospheric observations show that energy must be released at very small spatial scales (smaller than 100 km), and therefore, the intricate fine structuring of the magnetized chromosphere is the key to understand the heating and the mass loading of the outer atmosphere. The CHROMIS instrument at the Swedish 1m Solar Telescope (SST) is the only instrument in the world that allows observing the upper chromosphere at this spatial resolution, and rich spectral resolution.

SUNMAG shall use observations from this instrument and a space-borne solar telescope (NASA\'s Interface Region Imaging Spectrograph, IRIS) to reconstruct time-dependent 3D empirical models of the solar chromosphere. We will use these models to characterize the spatio-temporal distribution of heating in the chromosphere of active regions and flares, and to investigate to what extent this heating can be related to the observed (changes in) the physical parameters. These results will be confronted with predictions from the foremost theoretical models to propose what physical mechanisms are most likely providing the required energy deposition.

The main scientific questions that SUNMAG will address are:
1. What are the amount and distribution of energy that is released in the chromosphere of magnetically active regions and flares?
2. What are the physical mechanisms responsible of releasing this energy?
3. What is the physical state of the solar photosphere and chromosphere when flares are triggered and how is flare triggering related to the chromospheric magnetic field configuration?

This project is directly related to the magnetic activity and explosive events that produce space weather. Space weather can have a direct influence on our society, especially disrupting satellite operations and affecting the power grids as a consequence of the magnetic activity on the Sun.

Work performed

During the first period of SUNMAG, we have reached the following milestones of the project:
1. We have recruited 3 postdocs and 1 PhD student who are now working for the project.
2. We have acquired all the data that are required for the project. The observations were performed in 4 campaigns between 2018-2019 and we still have observing time available at the Swedish 1-m Solar Telescope for 2020. All observations were coordinated with NASA\'s IRIS satellite that co-observed our targets.
3. We have implemented the first proof-of-concept code with new analysis methods for our data. We are currently implementing these ideas in our general purpose analysis code.
4. We have started analysing flare data and active region data.

Final results

The SUNMAG project aims at producing realistic 3D model atmospheres of the solar photosphere and chromosphere in order to study chromospheric heating mechanisms.
In order to produce such models, we have combined three techniques that were not used before in similar studies. These techniques are:
1. the inclusion of many chromospheric and photospheric spectral lines in one simultaneous data inversion.
2. the inclusion of vertical and horizontal regularization in order to constrain the parameters of the inferred models.
3. a proper 2D treatment of spatial instrumental effects in order to be able to combine data from different facilities acquired at different resolution.

Techniques 1. and 2. are already implemented in STiC (our analysis code), whereas we have just finished developing technique 3. using a proof-of-concept code.
We are currently implementing it in STiC.

We have acquired very high quality spectropolarimetric datasets with the new CHROMIS instrument at the highest spatial resolution that is available at the moment (~75 km at the surface of the Sun) in combination with diagnostics from the CRISP instrument at the Swedish 1-m Solar Telescope and with NASA\'s IRIS satellite in the ultraviolet. We have observed several flaring active regions, which are excellent targets for the SUNMAG projects.

We have also developed a technique for de-noising of polarimetric data using deep-learning methods. This method uses spatial coherency in the polarimetric images in order to increase the signal-to-noise ratio of the observations. The latter is crucial for the inference of the magnetic field vector on the surface of the Sun with inversion methods.