Observing and understanding flux emergence using IRIS and SST coordinated data

In 1908 the Sun became the first star on which magnetic fields were detected by Hale). Since then the solar community has developed different methods and instrumentation in order to measure these magnetic fields, and has tried to explain their effect on our nearest star as well as on the heliosphere surrounding it. The genesis and evolution of the solar magnetic field is the key ingredient in understanding the workings of the active Sun. The emergence of flux into the solar atmosphere is an important element in the life cycle of the solar magnetic field and the study of magnetic flux emergence is a fast developing subject which relies heavily on the current rapid development of observational capabilities and of high performance computational resources and techniques. The outer solar atmosphere is heated and solar activity arises as a result of the interaction between the motions in the convection zone and the magnetic field. Much progress in understanding the relevant processes has been made in the last decade, not least due to great improvements in the realistic modeling of this interaction. However, there are also significant discrepancies between the observations and the simulations. A major goal of this project is to determine whether some of these discrepancies are due to the neglect of flux emergence. Furthermore, measuring magnetic fields in the photosphere, below the chromospheric forcing, is not good enough to understand how the magnetic field shapes the outer atmosphere and drives not only heating of the solar atmosphere, but also flares and coronal mass ejections. During the project data were collected and models computed of flux emergence as magnetic field rises into the outer layers of the Solar atmosphere. The observational data was collected at the Swedish 1-meter Solar Telescope on La Palma and simultaneously by IRIS, an American satellite that is sensitive to light from the Sun's outer layers. The data show how rising magnetic field is the source of explosions (Ellerman Bombs and UV bursts) both in the photosphere and higher in the chromosphere. The numerical models have contributed to the understanding of how these phenomena are connected. This is an important process, not only for the understanding of Ellerman Bombs and UV bursts, but also in and of itself: The emergence of field through the photosphere is the first step in the formation of so called active regions on the Sun, where enormous sunspots as well as smaller magnetic elements are the ultimate source of the most energetic phenomena that occur on the Sun, resulting in the ejection of both plasma and highly energetic particles. These generate space weather with consequences for both the Earth?s, but also Venus? and Mars? climate and magnetospheres. The project found that the combination of analyzing the data and comparing it with the numerical model, led to an understanding of the relationship between Ellerman Bombs and UV Bursts for the first time. The emerging flux in strong field regions can result in long current sheets that can stretch from the photosphere to the upper chromosphere with resulting energetic explosions where reconnection occurs along the current sheet. These explosions produce synthetic observables from the numerical simulation that matches the real solar data. During the projects last year the two aspects: numerical modeling and observations with the SST and IRIS were written up and presented in two articles: ?Ellerman bombs and UV bursts: transient events in chromospheric current sheets?, 2019, Hansteen et al., A&A 626, 33 and ?Ellerman bombs and UV bursts: reconnection at different atmospheric layers?, 2019, Ortiz et al., 2019. The first article is already in print, the second is completed and will be sent to the magazine Astronomy & Astrophysics before the end of August 2019. These papers have been presented in several meeting during the fall of 2018 and the spring of 2019: at the SDO meeting in Ghent, the Flux Emergence Workshop in Tokyo, and the Nordita Workshop on helicity in Stockholm.

Virkninger: To prosjektdeltagere har vært nært knyttet til dette prosjektet. Begge har styrket sin faglige selvtillit og status utad og er dermed blitt mere ettertraktede medarbeidere både nasjonalt og internasjonalt. Arbeidet har foregått som et underprosjekt i et Forskningsrådsfinansiert "Senter for Fremdragende Forskning" - The Rosseland Center for Solar Physics (RoCS). RoCS-senteret har også fått økt internasjonal oppmerksomhet som virkning av prosjektet. Effekter: Forståelsen av hvordan aktive områder bygges opp og utviklingen av solens magnetfelt over tidskalaer som går fra timer til ti-år er et viktig forskningsfelt. Dette vil i de neste ti-årene hjelpe oss forstå hvordan magnetfelt på solen og på andre stjerner blir dannet og vedlikeholdt, viktig med hensyn på koblingen mellom solens aktivitet og jordens magnetosfære, hvordan jordens klima påvirkes og hvordan strålingsfaren i det interplanetære rom kan forstås.

We apply for funds to observe, analyse and understand small scale magnetic flux emergence into the Sun?s outer atmosphere. While the flux emergence of photospheric small-scale structures already are well observed and understood, our knowledge of their counterparts at higher layers is insufficient, as is the fate of the rising magnetic field and how it couples the different regions of the atmosphere. We will use the Institute of Theoretical Astrophysics (ITA)'s access to state-of-the-art ground and space-based facilities, complemented by 'realistic' 3D simulations of the outer solar atmosphere to determine the fraction of weak internetwork photospheric flux that reaches the chromosphere and transition region; to analyse the ubiquitous magnetic flux emergence process that occurs at all spatial and temporal scales; and to measure the chromospheric magnetic field itself.