Periodic Reporting for period 4 - SolMAG (Unravelling The Structure and Evolution of Solar Magnetic Flux Ropes and Their Magnetosheaths)
Reporting period: 2021-12-01 to 2023-05-31
This project studies Coronal Mass Ejections (CMEs) – gigantic eruptions of plasma and magnetic field from the Sun in the form of magnetic flux ropes - and their turbulent sheath regions. CME flux ropes and their sheaths are key agents of driving strong space weather storms at Earth that can have significant consequences for our space assets in orbit and their related applications (e.g. communication) and for many ground technological systems with substantial economic losses. The key parameter to determine a CME’s ability to disturb our near-Earth space is its magnetic field (direction and magnitude). The magnetic field, however, cannot currently be determined in advance and must be measured directly. This severely limits the current accuracy of space weather forecasting and the understanding of the physics behind the initiation and evolution of CMEs. Another big issue is that the turbulent sheath ahead of CMEs is currently poorly understood. In addition, CME‐driven sheaths present a unique natural environment to study fundamental plasma physical processes.
The SolMAG project aims to derive realistic estimates of the magnetic field in both CME flux ropes and sheaths from Sun to Earth. The project Work Packages (WPs) and their key overall objectives are
WPA “Quantification of Magnetic Structure and Evolution of CME Flux Ropes” analyses CME flux ropes from the point of their formation at the Sun until sampled in-situ. The key objective of WPA is to deliver realistic information on the intrinsic magnetic structure of CMEs at the time of the eruption and its early evolution in the low corona (few first solar radii).
WPB “Comprehensive Characterization of CME Sheaths Regions” studies CME sheaths using a comprehensive in-situ analysis and simulations. Sheaths accrete gradually as CMEs plough supersonically through interplanetary space and physical processes at the shock and at the flux rope leading edge lead to highly irregular and complex structure. The key objectives of WPB are to quantify the occurrence of various plasma waves in CME sheaths and the nature of turbulence.
WPC “Sheath and CME Interactions” studies coupling of turbulent sheaths to Earth’s magnetosheath and one of the most complex processes related to CMEs - the merging of multiple eruptions. The key objectives are to detail how multi-scale CME sheath fluctuations transfer to the Earth’s magnetosheath and use our data-driven simulations and in-situ observations to study CME-CME interactions with flux ropes that have different magnetic structure.
The SolMAG project aims to derive realistic estimates of the magnetic field in both CME flux ropes and sheaths from Sun to Earth. The project Work Packages (WPs) and their key overall objectives are
WPA “Quantification of Magnetic Structure and Evolution of CME Flux Ropes” analyses CME flux ropes from the point of their formation at the Sun until sampled in-situ. The key objective of WPA is to deliver realistic information on the intrinsic magnetic structure of CMEs at the time of the eruption and its early evolution in the low corona (few first solar radii).
WPB “Comprehensive Characterization of CME Sheaths Regions” studies CME sheaths using a comprehensive in-situ analysis and simulations. Sheaths accrete gradually as CMEs plough supersonically through interplanetary space and physical processes at the shock and at the flux rope leading edge lead to highly irregular and complex structure. The key objectives of WPB are to quantify the occurrence of various plasma waves in CME sheaths and the nature of turbulence.
WPC “Sheath and CME Interactions” studies coupling of turbulent sheaths to Earth’s magnetosheath and one of the most complex processes related to CMEs - the merging of multiple eruptions. The key objectives are to detail how multi-scale CME sheath fluctuations transfer to the Earth’s magnetosheath and use our data-driven simulations and in-situ observations to study CME-CME interactions with flux ropes that have different magnetic structure.
We performed the first fully data-driven and time-dependent magnetofrictional method (TMFM) simulations of erupting flux ropes in the inner corona using realistic boundary conditions. This approach thus provides self-consistently an estimate of the magnetic structure of the CME flux rope with only magnetograms from the surface of the Sun used as a boundary condition to drive the model. In the later phase of the project the TMFM simulation was coupled with a zero-beta magnetohydrodynamic (MHD) model. We were able to produce with these linked models a stably erupting flux rope which is a big step forward. Our method is computationally efficient, and thus, has the potential to be used in near-real time space weather forecasting. Our latest published results on exploring the optimization of the electric field inversion parameters and contribution to work of developing the automated flux rope extraction tool from the simulation data also support the applicability to space weather forecasting. The project also resulted in a novel scheme to estimate the magnetic structure of flux ropes using a synthesis of several proxies based on remote-sensing solar observations. In particular, our simulation/observational results have been used to constrain magnetized CME flux ropes in our state-of-the-art numerical space weather simulations (e.g. European space weather model EUHFORIA). Our studies using direct solar wind measurements from pairs of lined-up spacecraft revealed that the magnetic field structure of CME flux ropes typically does not significantly change in interplanetary space, but in case of interactions significant deviations can occur even at relatively short heliospheric distances. The outcome of such interaction depends strongly on the magnetic structure of CMEs and our study also highlights the importance of having realistic information of intrinsic CME magnetic fields, accurate modelling of CME propagation in the heliosphere and multi-spacecraft observations.
Our comprehensive analysis showed that certain types of plasma waves (mirror mode and ion acoustic waves) are ubiquitous in CME sheaths, in particular close to the CME-driven shock, and they form at the early stages of CME evolution. Our extensive analyses on magnetic fluctuations and turbulent parameters in CME sheaths have revealed that they are likely combinations of processed fluctuations and new fluctuations generated at shock/sheath processes, but that CME-driven shocks are not resetting the turbulence in a similar manner as planetary bow shocks. The results give information of the properties and locations of the most intense fluctuations and how they relate to driver and upstream properties. The importance of small scale structures and slow CMEs having also prominent sheaths was highlighted by our work. Characterising turbulence and plasma waves in sheaths is also highly important for space weather forecasting. Our project studies have also demonstrated turbulent CME-sheaths perturb particularly strongly the Van Allen radiation belts that circle the Earth. High-energy electrons in the belts are a significant threat to satellites orbiting in that region.
The results have been disseminated to scientific community via publications in the leading journals of the field, active participation of conferences and workshops and via social media (Twitter)
Our comprehensive analysis showed that certain types of plasma waves (mirror mode and ion acoustic waves) are ubiquitous in CME sheaths, in particular close to the CME-driven shock, and they form at the early stages of CME evolution. Our extensive analyses on magnetic fluctuations and turbulent parameters in CME sheaths have revealed that they are likely combinations of processed fluctuations and new fluctuations generated at shock/sheath processes, but that CME-driven shocks are not resetting the turbulence in a similar manner as planetary bow shocks. The results give information of the properties and locations of the most intense fluctuations and how they relate to driver and upstream properties. The importance of small scale structures and slow CMEs having also prominent sheaths was highlighted by our work. Characterising turbulence and plasma waves in sheaths is also highly important for space weather forecasting. Our project studies have also demonstrated turbulent CME-sheaths perturb particularly strongly the Van Allen radiation belts that circle the Earth. High-energy electrons in the belts are a significant threat to satellites orbiting in that region.
The results have been disseminated to scientific community via publications in the leading journals of the field, active participation of conferences and workshops and via social media (Twitter)
One of the most significant progresses beyond the state of the art achieved during the project are the several successful modelling erupting flux ropes with our data-driven and time-dependent magnetofrictional method (TMFM) simulation. The results also match well with the coronal extreme ultraviolet (EUV) observations of eruptive structures. These include also linking TMFM to zero-beta magnetohydrodynamic (MHD) model. They provide a computer efficient manner to extract intrinsic CME parameters. Additionally, a new method to derive twists in solar flux ropes was developed.
Our analysis of sheath regions has provided a wealth of new understanding of magnetic field fluctuations and turbulence in sheath regions. This has also included using new tools in this context, i.e. information theory tools to explore the nature of fluctuations.
The work has also opened several new horizons to continue to research e.g. expand the use of information theory tools for sheath and other solar wind structure studies and integrating lower coronal simulations as standard space weather forecasting tools.
Our analysis of sheath regions has provided a wealth of new understanding of magnetic field fluctuations and turbulence in sheath regions. This has also included using new tools in this context, i.e. information theory tools to explore the nature of fluctuations.
The work has also opened several new horizons to continue to research e.g. expand the use of information theory tools for sheath and other solar wind structure studies and integrating lower coronal simulations as standard space weather forecasting tools.