Rosseland Centre for Solar Physics, Rosseland senter for solfysikk (RoCS)

The vision of the centre is “understanding the workings of the energetic Sun”. Solar magnetism lies at the root of most solar and heliospheric physics. The magnetic field is generated by enigmatic dynamo processes in the solar interior, is organized into the complex patterns of activity observed in the solar photosphere, dominates the energetics of the outer solar atmosphere (chromosphere, transition region, corona), regulates the solar wind, and affects the extended heliosphere into the Earth's upper atmosphere. We will achieve a coherent picture of these complex physical processes through confronting state-of-the-art 3D numerical models of the entire region from the upper convection zone to the corona with comprehensive observations of the entire solar atmosphere from a powerful suite of new observatories. Project start was November 1st, 2017. A scientific highlight was the publication of the first results from the CHROMIS instrument on the Swedish 1-m Solar Telescope on La Palma. The observations show intermittent reconnection and plasmoids in UV bursts in the lower solar atmosphere. The solar magnetic field is generated in dynamo processes in the interior. The magnetic field gives rise to activity at all scales, like solar flares and smaller explosions and jets. In 2018 we have made computer simulations that can explain several of these phenomena. The results have been presented at conferences and the first paper was published in 2019. A new international project got selected for funding in 2018: The ERC Synergy grant WHOLE SUN. We here work with groups in Paris, Göttingen, St. Andrews and Tenerife. The WHOLE SUN project attempts to link the eruptive phenomena observed in the solar atmosphere to the motions of plasma deep in the interior of the Sun, where its magnetic field is generated. We strengthened RoCS in 2019 and 2020 through several hirings. An important strengthening of our scientific breadth was the hiring of three eminent scientists in 20% positions: professor Åke Nordlund from University of Copenhagen, professor Ineke De Moortel from University of St.Andrews and Dr. Juan Martínez Sykora from Lockheed Martin Solar and Astrophysics Laboratory. The high activity continued in 2020. We arranged two international meetings in our premises in January and March, before the Covid-19 lock-down. The activity of RoCS is very international, so the pandemic was a hard blow. Two other international meetings and several longer guest researcher visits had to be cancelled. Researchers at RoCS have strong roles in the Solar Orbiter project. A highlight was the launch of Solar Orbiter on February 5th, 2020, and the successful testing of the instruments. The first results were shown at the meeting of AGU in December 2020. Researchers at RoCS have had central roles in the proposal of a new NASA solar satellite, Multi-slit Solar Explorer (MUSE). Our simulations of various processes in the solar atmosphere have been used to simulate how observations from the proposed satellite can discriminate between different models of coronal heating and solar explosions. The work was instrumental in getting MUSE selected by NASA in February 2022 for launch in June 2027. Principal investigator for MUSE is Bart De Pontieu, adjunct professor at RoCS. RoCS also has three co-investigators (Mats Carlsson, Viggo Hansteen og Juan Martínez Sykora). Every three years the European Solar Physics Meeting is organized by the European Solar Physics Division (ESPD) of the European Physical Society. In 2021 the meeting was organised as a digital meeting. Being the general secretary of ESPD, Tiago Pereira at RoCS was responsible for running the meeting with the help of five students/postdocs at RoCS. With 639 participants and 417 talks, this was probably the largest solar physics meeting ever. The ERC Synergy grant project “Whole Sun” has as a goal to model the whole Sun as one object. We achieved a breakthrough in 2022: through an innovative domain decomposition inspired by the making up of a Volleyball it was possible to map the spherical Sun with cubic patches at slight angles.. The algorithms were published in two papers in November 2022. In 2023 we got an allocation of 167 million core-hours on the LUMI supercomputer in Finland in the first Euro HPC Extreme Scale Access program. We are now using this allocation to relax the simulation cube and prepare to attack some of the most challenging problems in the RoCS research plan. The ongoing NASA mission IRIS and the new mission MUSE are central for realizing the RoCS vision. In February/March 2023 we organized an international scientific meeting in Longyearbyen, Svalbard. The RoCS/MUSE/IRIS meeting (dubbed RoCMI) gathered 100 eminent scientists for one week of intense discussions with both northern lights and a visit to SvalSat – the downlink station for data from IRIS and MUSE.

The overarching goal of the project is understanding the workings of the energetic Sun. We wil do this by creating an international centre of excellence that will push the boundaries of solar physics by exploiting and extending the unique combination of cutting edge expertise in observational data and numerical simulations at the Institute of Theoretical Astrophysics, University of Oslo. Solar magnetism lies at the root of most solar and heliospheric physics. The intricate structure and dynamics of the solar field and its influence on the heliosphere represent major quests of (astro) physics which bear directly on the human environment. The magnetic field is generated by enigmatic dynamo processes in the solar interior, is organized into the complex patterns of activity observed in the solar photosphere, dominates the energetics of the outer solar atmosphere (chromosphere, transition region, corona), regulates the solar wind, and affects the extended heliosphere into the Earth's upper atmosphere. We will achieve a coherent picture of these complex physical processes through confronting state-of-the-art 3D numerical models of the entire region from the upper convection zone to the corona with comprehensive observations of the entire solar atmosphere from a powerful suite of new observatories. We will exploit the recent advances in supercomputing and expand our current computational capabilities beyond the state of the art by implementing new research methods such as multi-fluid and particle-based models. Understanding the workings of the energetic Sun is an ambitious goal and an important research focus for the international solar physics community. Our proven track record in understanding and integrating simulations and observations into a coherent picture of the quiet solar atmosphere puts the centre in an excellent position to tackle the more complex challenges presented by the energetics of the active Sun and bring the field to a new level.