MAGHEAT: understanding energy deposition in the solar chromosphere

Project Information

MAGHEAT

Grant agreement ID: 101088184

DOI

10.3030/101088184

EC signature date 25 February 2023

Start date 1 July 2023

End date 30 June 2028

Funded under

• European Research Council (ERC)

Total cost

€ 1 994 937,50

EU contribution

€ 1 994 937,50

Coordinated by

STOCKHOLMS UNIVERSITET
Sweden

Periodic Reporting for period 1 - MAGHEAT (MAGHEAT: understanding energy deposition in the solar chromosphere)

Reporting period: 2023-07-01 to 2025-12-31

Summary of the context and overall objectives of the project

The solar chromosphere and the million-degree corona are not in radiative equilibrium with the photosphere. This is most evident in the temperature stratification of empirical models of the outer solar atmosphere, where a steep temperature increase outward is required in order to explain the observed intensities. Furthermore, the chromosphere is radiating on average 4 kW/m^2 in the quiet Sun and 20 kW/m^2 on active regions, which cannot be explained by radiative transport alone. Therefore, additional energy transport and dissipation mechanisms (besides radiation) must be at work in order to explain the derived temperature gradient and the non-zero radiative losses predicted 1D empirical models: 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 heating is very intense in magnetically active regions. Large-scale magnetic fields emerge on the solar surface as an integral part of the 11-year-solar-cycle, and they greatly affect the outer layers of the Sun. Transient magnetic activity is ultimately responsible for the coronal mass ejections and flares which cause space weather events, and it plays a fundamental role in heating the outer layers of the Sun. The importance of the chromosphere and its magnetic field is highlighted by the scientific focus of a
new class of forthcoming 4m solar telescopes that have been designed with the prime objective of studying the chromosphere. These telescopes include dedicated instrumentation to study chromospheric dynamics and magnetic fields: DKIST in USA and the European Solar Telescope.

The main scientific questions that MAGHEAT will address are:
1. How is the energy transported and released into the chromosphere?
2. What is the role of currents, waves, turbulence and particle acceleration and kinetic energy deposition in the chromospheric heating problem?
3. How much magnetic energy is stored in a pre-flare system and how much energy is released during the flare by electron beams in the chromosphere? What are the conditions that lead to trigger a flare?

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the first part of the project we have achieved the following milestones:
1) Hiring of a research team.
2) Design and installation of a new polarimeter in the CHROMIS instrument. This instrumental development will allow for magnetic field estimates in the upper solar chromosphere.
3) Successful acquisition of co-temporal datasets with instrumentation at the Swedish 1-m Solar Telescope (CRISP and CHROMIS, both with polarimetry) and NASA's IRIS satellite.
4) Development of the physics included in our inversion code (on-going): a magnetohydrostatic 3D pressure balance, global operator implementation for the radiative transfer part, efficient Krylov-Newton solver for the radiative transfer part, derivatives of the partial redistribution problem, consolidation of the multi-resolution inversion module, development of an general equation of state with analytical derivatives.
5) On-going studies of chromospheric heating in flares and evolution of magnetic fields.
6) Implementation of temporal regularization to improve the reconstruction of magnetic fields.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

We are undertaking a major effort in instrumental and analysis software developments. Results beyond the state-of-the-art so far are:
1. The successful implementation of spatio-temporal regularization in the inversion technique.
2. The acquisition of the first diffraction limited dataset of a flare with CRISP and CHROMIS both operating in full-Stokes mode.

The solar chromosphere observed in the core of the Ca II K line, acquired with CHROMIS at the SST