Description of the objective:
CME initiation has been a core space physics problem for the last three decades. The two current paradigms (see figure) are distinguished primarily by the topology of the pre-eruption magnetic field: twisted flux rope (e.g., Roussev et al., 2004) or sheared arcade (Antiochos et al., 1994). Irrespective of the pre-eruption topology, all models predict that as a result of the flare reconnection occurring below the ejection, CMEs in the heliosphere must have a twisted flux rope topology, as commonly observed (Gosling et al., 1995). If the pre-eruption topology is that of a twisted flux rope, then the innermost part of its structure should exhibit relatively undisturbed filament plasma parameters. However, if the twist forms only as a result of flare reconnection, then the whole twisted structure in the heliosphere should exhibit the properties of flare-reconnection-heated plasma, hot beamed electrons, high charge states of Fe, as well as compositional anomalies of heavy ions including He. By measuring the electron and ion properties of a CME along with its magnetic structure, we determine the pre-eruption topology and the initiation mechanism. Solar Orbiter will provide the opportunity to perform these measurements near the Sun, minimizing propagation effects such as internal reconnection, which homogenizes the CME structure (e.g., Lynch et al., 2005).
Pre-eruption fields of the break-out model and the flux rope model. Adapted from Antiochos et al. 1999 and Fan, 2005.
- Target: Prominence, Active Regions, Flaring Regions.
- Observing mode: CME Watch, Composition mapping (with possibility to measure Doppler velocities).
- Slit size: 4” for CME Watch, 6” for Composition mapping.
- Exposure time/cadence and number of X positions: 30 s, X=224 for CME Watch, 100 s, X=160 for Composition mapping.
- Field of View: 15’×11’ for CME Watch, 16’×11’ for Composition mapping.
- Number of repetitions of the study: Repeat for different targets.
- Observation time per day: 1.9 hours per study for CME Watch, 4.4 hours per study for Composition mapping (the total observation time depends on the number of targets).
- Key SPICE lines to be included: C III 977 Å, O VI 1032 Å, O VI 1037 Å, Ne VIII 770 Å, Mg IX 706 Å, Fe X 1028 Å and Fe XX 721 Å (the last line in case of a flare)– 15 lines (5 profiles+10 intensities) for CME watch; Ne VIII 770 Å, Ne VIII 780 Å, Mg IX 706 Å, O II 718 Å, O IV 787 Å, O V 760.4 Å, O V 761 Å, O VI 1032 Å, O VI 1037 Å, Ne VI 999 Å, Ne VI 1010 Å, Mg VIII 772 Å, Mg VIII 782 Å, C III 977 Å, Fe III 1017 Å - 2 profiles and 13 intensities or 4 profiles and 11 intensities (maximum of 15) for Composition mapping.
- Observing window preference: Close to perihelion is preferred.
- Other instruments: EUI, PHI, METIS, SWA, EPD, SoloHI.
- Comments: The choice of lines, and also the number of intensities and profiles, is flexible, although the sum of the intensities and profiles is constrained to a maximum (e.g 15 for composition mapping). While varying the number of intensities and profiles, within the maximum, has no effect on the duration of the study, it will have an effect on the telemetry.
In addition, a stealth CME refers to an eruption that shows only weak signatures in EUV/UV data yet is observable by a coronagraph. Stealth CMEs can be geo-effective and are therefore of interest for space weather forecasting. There are still open questions about the formation and eruption of these structures.
Proposed observing plan:
PHI - synoptic data (1 day cadence)
EUI - FSI 174A with 5 minute cadence
METIS - 30 minute cadence
Especially suited in case of quadrature with Earth.