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Space- and ground-based coronagraphs, together with EUV space-based imagers, are the only instruments capable of providing observations of Coronal Mass Ejections (CMEs) from their early acceleration phases to interplanetary propagation. As the study of these phenomena is key for our understanding of how the Sun interacts with planets and modulates the whole Heliosphere, coronagraphs will be on-board the recently launched and upcoming solar missions, such as the ESA Solar Orbiter and PROBA-3 missions, the Chinese ASO-S mission, the Indian Aditya-L1 mission. These future coronagraphs will provide a new capability that was almost unexplored so far: the acquisition of coronagraphic images in multiple narrow-band spectral ranges, from visible light (VL) to ultraviolet (UV). Moreover, next space- (Aditya-L1/VELC) and ground-based coronagraphs (UCoMP, CorMAG) will acquire spectro-polarimetric observations to measure the weak coronal magnetic fields. The analysis of these innovative data will require the development and testing of new diagnostic techniques to determine not only the CME plasma densities (usually done from broad-band VL images), but also other parameters such as the electron temperature, line optical thickness, filling factors, and magnetic fields. The goal of the proposed Team at ISSI-BJ is to investigate how the CME properties affect the expected emission in the future multi- waveband coronagraphic observations, with the aim of developing new diagnostic techniques to tackle the open science questions on CMEs. This will be done by building synthetic data based on existing MHD simulations, testing new diagnostics with synthetic data inversion, and by applying the newly developed techniques to existing and future data.
 
Below you can find the presentations and files displayed during the online meetings in January 2021.



Motivations

Although CMEs have been intensively studied in the past, their origin is still not fully understood: CMEs are associated with regions of strong magnetic field (e.g. active regions), but we still have very little information on the properties of the source magnetic structure and plasma within the CME source region, and on the precise sequence of events leading to an eruption. in the intermediate corona (above ~ 1.7 solar radii) CMEs have been observed mainly from space-based (e.g. SOHO/LASCO, STEREO/COR1-2) and ground-based (e.g. Mauna Loa MarkIV and CoMP) coronagraphs, primarily in the polarized and unpolarised VL emission from coronal plasmas. Only the SOHO/UVCS provided the UV spectra in a limited field-of-view (FOV) and usually not accompanied by VL observations, and revealed unexpected thermodynamic behaviours, with plasma heating processes exceeding adiabatic cooling whose origin is still unidentified. Nevertheless, the only CME plasma physical parameters usually investigated with coronagraphic data are limited to the electron density, and to large-scale CME kinematical properties, even if spectro-polarimetric observations have proven their capability to derive other plasma parameters. For the above reasons, many science questions on CMEs remain open.

Currently available coronagraphic data have already proven their potential, but also their limits. Fortunately this situation will change in the near future with the new generation multi-waveband coronagraphs, whose new data will allow to answer most of the above questions. In particular, over the next few years, the following new coronagraphic instruments (among others) will become operational in space and on-ground:

  • Metis on-board Solar Orbiter ESA mission, launched in February 2020
  • ASPIICS on-board PROBA-3 ESA mission, launch in 2021
  • LST on-board Chinese ASO-S mission, launch in 2022
  • VELC on-board Indian Aditya-L1 mission, launch in 2020-2021
  • UCoMP installed at Mauna Loa Observatory, functional in 2020

Thanks to their multi-wavelength capabilities, all the above instruments will really enable a new perspective on solar eruptions. However, only the combination of these data with new observations acquired at the same time in different EUV, UV and visible spectral ranges can really enrich our knowledge of solar eruptions.

Goals

To efficiently extract new information from data of the future coronagraphs listed above and to answer the aforementioned compelling science questions which drive this Project, it is necessary to develop new diagnostic techniques and tools, which are anchored in the existing data. For this reason, the Project will focus on the early phases of the CME formation and propagation in the corona, a field where extended data archives from space-based SOHO, STEREO, SUVI, and ground-based COMP, KCOR, etc, can be effectively explored. Moreover, because many different spectral bands will be observed, it is necessary to provide and analyse synthetic observables from various MHD simulations. These main objectives will be achieved with the goals listed below.

  • First goal: to employ already existing 3D datacubes from numerical simulations of CMEs to derive the corresponding 3D distribution of different ions in CMEs responsible for the main emissions in the wavebands of future instruments listed above. These will be derived with and without the assumption of ionization equilibrium.
  • Second goal: to simulate the future appearance of CMEs and erupting prominences building synthetic coronagraphic data in different filters and different FOVs that will be provided by the Metis, ASPIICS, LST, VELC, and UCoMP instruments. This will be done both with and without the assumption of ionization equilibrium, and treating in a different way optically thin and optically thick parts of CMEs.
  • Third goal: to develop new diagnostic techniques to invert synthetic data to derive not only the plasma density, but also 2D plasma temperatures distribution inside CMEs, as well as information on the coronal magnetic fields involved in the eruption in the early expansion phases. The plasma parameters from synthetic data inversion will be compared with input parameters from the model to test and optimize the inversion methods. The diagnostic tools will also be applied to the real data of CMEs in existing archives to check various instrumental effects and test on the diversity of CME observations which might not be fully covered by our numerical simulations.

Meeting schedule

Due to the ongoing pandemic emergency, the first meetings have been organized remotely with Zoom. The regular "face-to-face" meetings will be organized as soon as possible; we plan to meet for two one-week meetings at ISSI-Beijing.

Remote meetings: January 13, January 20, January 27

Team members

Almost all the Team members are actively involved and have important roles in the different instruments/projects mentioned above, and in particular in Solar Orbiter/Metis (Bemporad, Heinzel, Pagano, Susino, and Jejcic), PROBA-3/ASPIICS (Bemporad, Heinzel, Jejcic, and Mierla), ASO-S/LST (Feng, and Li), Aditya-L1/VELC (Banerjee), and UCoMP (Tian). Moreover, the Team members have great experience in many different research fields including the analysis of coronagraphic VL images and EUV-UV images and spectra of CMEs (Banerjee, Bemporad, Feng, Mierla, Susino), analysis of prominence observations and non-LTE radiative transport modelling (Heinzel, Jejcic), numerical simulations and synthetic data (Pagano, Lin), derivation of coronal magnetic fields (Tian).

  • Alessandro Bemporad (Leader), INAF-Turin Astrophysical Observatory, Italy
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  • Li Feng (Co-leader), Purple Mountain Observatory, China
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  • Dipankar Banerjee (member), Aryabhatta Research Institute of Observational Sciences , India
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  • Petr Heinzel (member), Academy of Sciences of the Czech Republic
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  • Sonja Jejcic (member),University of Ljubljana, Slovenia
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  • Hui Li (member), Purple Mountain Observatory, China
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  • Jun Lin (member), Chinese Academy of Sciences, China
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  • Marilena Mierla (member), Royal Observatory of Belgium
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  • Paolo Pagano (member), School of Mathematics and Statistics , UK
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  • Roberto Susino (member), INAF-Turin Astrophysical Observatory, Italy
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  • Hui Tian (member), Peking University, China
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  • Beili Ying (member), Purple Mountain Observatory, China
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