Description of the objective:
- Full characterization of photospheric magnetic fields: the magnetic field at the photosphere can be determined quantitatively by recording the full polarization state of light in appropriate spectral lines. Such measurements can be inverted to provide the full magnetic vector at the photosphere and the LOS component of the plasma flow velocity. These measurements will allow the emergence of magnetic flux to be determined, as well as its redistribution through its interaction with convection. From surface maps of the magnetic vector, it is possible to extrapolate the field into the Sun’s upper atmosphere, where its evolution gives rise to numerous dynamic and energetic phenomena. Time series of the velocity maps of the photosphere also allow a reconstruction of the subsurface structure using the techniques of helioseismology. Observations of the photospheric fields are, thus, essential for studying both the generation and atmospheric evolution of solar magnetic fields.
- Probe fine-scale structure of the solar photosphere, including waves and the emergence, evolution, and dynamics of magnetic flux. This needs PHI observations at high spatial resolution.
- Uncover the effects of waves and magnetic field changes on the upper atmospheric layers (e.g. production of transient events (Galsgaard et al., 2005)).
- Study of the magnetic fields at the poles of the Sun.
- The polar fields are responsible for the polar coronal holes and largely drive the fast solar wind, but are poorly known.
- Polar plumes are bright structures reaching far into the corona, which appear to harbor gas moving slowly, compared to the fast solar wind in the interplume regions. Observations of the magnetic field at their footpoints from high latitude will be crucial for an understanding of their origin. The aim is to provide sufficiently accurate and detailed magnetic maps, unhampered by the massive foreshortening that current observations suffer from, to allow high-quality extrapolations of the field.
- Origin of the spicules and other chromospheric features (De Pontieu et al., 2004). Polar spicules (Johannesson and Zirin, 1996). Spicules are a prominent chromospheric phenomenon, cool and dense fibrils that intermittently connect the photosphere with the hot and rarefied corona. They are short-lived (5-10 min), narrow (diameters less than 500 km) and display upward motions with speeds up to 20 km/s. If this is really mass motion, then the mass flux in spicules is 100 times larger than that of the solar wind. It has been shown that photospheric p-modes, which are evanescent in the field-free photosphere and chromosphere, can indeed propagate into and through the chromosphere if they are guided by inclined magnetic field lines (De Pontieu et al. 2004). Due to the steep vertical density gradient, the oscillations develop into shocks which may result in significant excursions of the top of the chromosphere, i.e. cause spicules. According to De Pontieu et al. (2004), the crucial ingredients for spicule formation are the photospheric velocities, the temperature stratification and the inclination of the magnetic field lines. However, it is well known that polar spicules are larger than ordinary spicules (Johannesson & Zirin 1996). They may, therefore, differ in cause. Viewing them from out of the ecliptic will advantageously reveal the underlying differences.
- Except for PHI/HRT (1 min cadence), EUI/HRI should observe at very high cadence (1-30s, possible for approximately up to 20 minutes), maybe interleaved with burst modes with high cadence (0.1 s, during 1 to a few seconds). The FoVs can be released if need be for telemetry reasons (for instance down to ¼ of the PHI/HRT FoV).
- SPICE could participate for a dynamics study with many rasters and a similar FoV. Alternatively, it could operate at a sit-and-stare mode.
- No other instruments are required.
- Due to its demanding nature in terms of telemetry, the relevant SOOP cannot be planned for long durations. It should be repeated whenever the telemetry budget configuration is favorable.
This objective is covered by the SOOP R_SMALL_HRES_HCAD_Atmospheric_Dynamics_Structure run for different targets at the quiet Sun (observed from the perihelion) and the coronal holes (observed from high-latitude windows). The SOOP L_SMALL_HRES_HCAD_Slow-Wind-Connection will also provide valuable information on photospheric structures but at lower spatial resolution.
- SPICE (updated by Alessandra Giunta 01/12/2015):
- Target: Quiet Sun or coronal holes; on disk
- Observing mode: Dynamics/Waves
- Slit: 2” for Dynamics; 4” for Waves
- Exposure time/cadence and number of X positions: 10 s, X=224 for Dynamics, 5s, X=720 for Waves
- Field of View: 7’×11’ for Dynamics, 4” ×11’ (sit and stare) for Waves
- Number of repetitions of the study: 3 for Dynamics; 2 for Waves
- Observation time: 1.9 hours (0.6 hours per study) for Dynamics; 2 hours (1 hours per study) for Waves – repeat the full 4 hours (Dynamics+ waves) if needed
- Key SPICE lines to be included: H I 1025 Å, C II 1036 Å, C III 977 Å, O VI 1032 Å, Ne VIII 770 Å, Mg IX 706 Å, Si XII 520 Å (x2) – 10 lines (4 profiles and 6 intensities)
- Observing window preference: Perihelion preferred for quiet Sun; high-latitude for coronal holes.
- Other instruments: PHI for magnetic fields; EUI for context imaging.
- 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.
- Possible binning on Y direction (group of 2 pixels).
- Repeat for 2 days (requested by PHI).
- SPICE will observe a sub-field of PHI field-of-view at high cadence and spatial resolution. The rasters could be mixed with sit-and-stare studies for high-cadence (wave) studies. For example, alternate each for 3-hour periods.