Solar atmospheric abundances in space and time

I will attempt to review and reflect on developments in the ponderomotive force model of the First Ionization Potential (FIP) effect, since its first presentation as a poster at the 2004 AAS meeting in Denver CO (May 30th – June 3rd), and as a talk at COSPAR in Paris later that summer (18th – 25th July). I will pay particular attention to how my understanding of the relevant wave physics has improved in that time. The ponderomotive force appears to have been a completely new means of ion-neutral separation in solar physics or astrophysics, though it was not new to science. Had I had my wits about me in 2004, I would have realised that this mechanism represents an analog in magnetohydrodynamics of the optical part of a magneto-optical trap. As it was, it wasn't until I read about Arthur Ashkin's Nobel Prize in 2018 in Physics Today that the penny dropped about the exact physics involved. The basic model, that the coronal magnetic field geometry dictates the properties of the Alfvén wave field through resonances and interference, and that these different wave properties give rise to the different FIP effects seen in different coronal structure still holds, though ideas about the wave origins have evolved. I will illustrate the varieties of FIP fractionation that can occur, how they relate to the underlying solar geometry, and how such phenomena may be used to investigate other aspects of solar physics.

Dr Martin Laming

Naval Research Laboratory, USA

Dr Martin Laming

Naval Research Laboratory, USA

Martin Laming has worked in the Space Science Division of the Naval Research Laboratory in Washington DC since 1990, becoming a federal employee in 1999, following a DPhil in atomic physics at Oxford University and a post-doctoral fellowship held at the Smithsonian Astrophysical Observatory in Cambridge MA. His research interests moved from highly charged ions in the laboratory to highly charged ions in space, notably the solar corona and wind, and in supernova remnants. He works on problems connected with elemental abundances and particle acceleration in both areas. He has been interested in wave-particle interactions throughout his career, beginning with his doctoral work measuring Lamb shifts to the current focus on MHD waves that accelerate the solar wind and cause FIP fractionation.

The enrichment of coronal loops and the slow solar wind with elements that have low First Ionisation Potential, known as the FIP effect, has often been interpreted as the tracer of a common origin. A current explanation for this FIP fractionation rests on the influence of ponderomotive forces and turbulent mixing acting at the top of the chromosome. The implied wave transport and turbulence mechanisms are also key to wave-driven coronal heating and solar wind acceleration models. In this talk, I will first show to use a shell turbulence model to assess the ponderomotive force in coronal loops and open field lines. With this model, we find that the turbulence power necessary to heat the corona and accelerate the solar wind is also able to generate the FIP effect. However, we do not find significant differences in the fractionation due to the geometry of the large scale magnetic field. Consequently, the second part of the talk will be focused on dynamic reconnection events in smaller scale loops, typical of coronal bright points. Using full 2.5D resistive MHD simulations, we shall investigate the ponderomotive force due to the reconnection induced perturbations in the coronal loops and the resulting FUP fractionation.

Dr Victor Reville

French National Centre for Scientific Research, France

Dr Victor Reville

French National Centre for Scientific Research, France

Victor Réville is an astrophysicist working at Institute de Recherche en Astrophysique et Planétologie (IRAP) in Toulouse, France. He is interested in solar and stellar winds, space plasmas, MHD turbulence and reconnection. He uses numerical simulations and theory to explain the in situ and remote sensing observations of space observatories like Parker Solar Probe and Solar Orbiter.

Departures from the single-fluid approximation can be expected in some regions of the solar atmosphere, eg the chromosphere is partially ionized and goes from a collisional to a weakly collisional regime. Similarly, some species behave as a magnetized fluid while others are unmagnetized in the lower chromosphere. In addition, species with different ionization potential populations vary depending on the regions in the corona, providing unique constraints for the drivers of coronal heating. Finally, but not least, there are observational indications of multi-fluid effects in the chromosphere, transition region, and high energetic events in the corona. We have been developing a new multi-fluid and multi-species numerical code: Ebysus. The code treats each excited/ionized level for each desired species as a separate fluid self-consistently, including physical processes such as thermal conclusion, ion-coupling, non-equilibrium ionization/recombination, collisions, and radiation. In this work, we briefly describe the capabilities of Ebysus and the first results of the FIP effect and chemical fractionation.

Dr Juan Martinez-Sykora

SETI Institute, USA

Dr Juan Martinez-Sykora

SETI Institute, USA

Juan Martinez-Sykora obtained his BSc, followed by his master's at the University of La Laguna (Spain) and continued his PhD in Solar physics at the University of Oslo. After that, he moved to Lockheed Martin Solar and Astrophysics Lab and Stanford University as a postdoc. Very soon he became a researcher at BAERI and LMSAL and adjunct associated professor at the University of Oslo. Nowadays, he is a senior researcher at SETI and LMSAL. Juan Martinez-Sykora's research focus on developing model for the solar atmosphere and comparing them to observations. In particular, he is interested in the effects of neutrals on chromospheric physics. Consequently, he is part of the Bifrost development team and the lead of the multi-fluid multi-species numerical code Ebysus. In addition, he has extensive experience performing IRIS planning, analysing observations, and comparing with numerical codes, including observatories such as SDO, Hinode, IRIS, ALMA, and ground-based observatories such as SST. He is highly involved in the development of MUSE (NASA MIDEX program) as science deputy lead. He has published more than 70 scientific papers in peer-reviewed journals.

Elemental abundances in the solar atmosphere, typically measured from EUV and X-ray observations, are often different from the solar photospheric abundances. The first ionization potential (FIP) of the element appears to be play a significant role in the observed fractionation, which is thought to be linked to the processes responsible for heating the solar atmosphere. In the solar atmosphere, elements with low FIP often show a relative enrichment with respect to elements with high FIP (FIP effect). The extent of such FIP effect is observed to vary broadly across solar features, with some solar features (such as eg most flares) showing an inverse FIP effect. Despite the widespread presence of chemical fractionation, and its potential importance for understanding the processes governing the solar atmosphere, this phenomenon and its original are still poorly understood.

We used coordinated coronal spectral observations taken with Hinode/EIS, and chromospheric and transition region spectral observations taken with IRIS, to investigate the presence of a footprint of the chemical fractionation process in the lower atmosphere. Such a footprint for the FIP effect is expected, given that the lower atmosphere is where most elements get ionized. We study the spatial and temporal properties of coronal chemical composition and corresponding chromospheric properties, for a variety of solar features. We discuss intriguing correlations between coronal abundances and chromospheric properties, which can potentially constrain models of chemical fractionation.

Dr Paola Testa

Harvard Smithsonian Center for Astrophysics, USA

Dr Paola Testa

Harvard Smithsonian Center for Astrophysics, USA

Dr Paola Testa is an Astrophysicist at the Harvard-Smithsonian Center for Astrophysics (USA). She received her doctorate in Physics at the University of Palermo (Italy) on the topic of coronal activity in the Sun and other stars, and then held a post-doctoral appointment at the Kavli Institute for Astrophysics at the Massachusetts Institute of Technology. Her research focused on understanding the heating mechanisms and high-energy processes in the hot outer layers of the atmosphere of the Sun and other stars by combining observations with advanced numerical modelling. She is also involved in development, observations, and dissemination of data of space instrumentation: she is co-investigator of several solar missions, including the Hinode/X-ray telescope (XRT, the Interface Region Imaging Spectrograph (IRIS), and the Multi-Slit Solar Explorer (MUSE, NASA Heliophysics Medium-Class Explorer to be launched in 2027).