Description of the objective:
- Understand dissipation involving cascading turbulence, current sheet collapse and reconnection, shocks, high-frequency waves and wave-particle interactions. Difference between resonant and stochastic?
- Understand oscillations in small-scale flux tubes (Jess et al., 2009; Martínez González, 2011; Stangalini et al., 2013; Requerey et al., 2015).
The scientific aim is to characterize the properties of waves in the photosphere and their coupling with the upper atmosphere, chromosphere, and corona.
Waves are one clear mechanism for transferring energy from the photosphere to the chromosphere and corona. Measuring the properties of the waves requires, in part, a determination of the velocity field. The line-of-sight velocity component can be determined at different heights in the atmosphere by observing Doppler shifts in different spectral lines. From the Earth’s vantage point we have high-resolution ground-based, balloon-borne, and satellite instruments. Determining the horizontal velocity has previously relied on using correlation tracking of intensity variations and rely on the questionable assumption that the changes in the location of the brightness fluctuations reflect the actual velocity. The orbit and capability to measure Doppler velocities, in conjunction with existing and upcoming ground-based or near-earth observatories, offers the unique chance to directly measure two components of the velocity field using the Doppler effect.
High-resolution co-temporal measurements including Doppler velocity maps from Solar Orbiter as well as ground and NEOs are required. In particular, the ground-based and NEOs should include high-resolution Doppler images in the same line (with a higher cadence than that of SO), as well as lines sampling different heights of the atmosphere. Co-observation with IRIS would be desirable. During the observing period, the Earth-Sun-SO angle should be between 30? and 60? – a range which represents a compromise between determining the two components of the velocity field and allowing magnetic features which can act as wave guides to be partially resolved.
For ease of understanding the connection between the different heights, the observations would best be performed at the center of the disk as observed from the Earth (where observations over different wavelengths are possible). Because also the achievable cadence will be higher on ground than with PHI, it is preferable to select targets which are closer to the disk center as seen from Earth and at higher heliocentric angles as seen from Solar Orbiter. The highest possible cadence is desirable, and a shorter time series (of down to 30 minutes of Solar Orbiter observations) would still allow the scientific objectives to be met. (The ground-based and NEO should be made for a period of 90 minutes centered on the 30 minute SO observations). However, in order to guarantee reliable conditions (seeing) at the coordinating ground-based observing facility (e.g. DKIST) a continuous high-cadence observation period of several hours is required.
High-resolution context magnetic maps from SO immediately before and after the 30 minute observing window are required to provide context and aid co-alignment.
A second observational campaign of an area 45? from disk center, with an Earth-Sun-SO angle of 90?, would be desirable.
This objective can be partly covered by the high-resolution high-cadence SOOP that studies the fine scale of the photosphere R_SMALL_HRES_HCAD_RS-burst and the SOOP R_SMALL_HRES_HCAD_Wave-Stereoscopy, which has been specifically designed for studying the properties of the waves in the photosphere.
The SOOPs should be run for a bright source (e.g. active region but also quiet sun) at the perihelion for a duration from 20 minutes to several hours. It would be preferable to address this objective earlier in the mission, because of the Lyα degradation with time.
- SPICE (updated by Alessandra Giunta 01/12/2015):
- Target: Quiet Sun, Active Regions, Coronal Holes
- Observing mode: Dynamics, Waves, 30” Wide Movie
- Slit: 2” for Dynamics, 4” for Waves, 30” for Wide Movie
- Exposure time/cadence and number of X positions: 5 s, X=128 for Dynamics; 5 s, X=720 for Waves; 5 s, X=120 for 30” Wide Movie (Fix Mirror for Waves and 30” Wide Movie, time series, multiple images)
- Field of View: 4’×11’ for Dynamics, 4” ×11’ for Waves; 30” ×14' for 30” Wide Movie
- Number of repetitions of the study: 5 for Dynamics followed by 3 for Waves and 1 for 30” Wide Movie
- Observation time: 1 hour for Dynamics (0.2 hours per study), 3 hours for Waves (1 hours per study), 0.175 hours
- Key SPICE lines to be included: H I 1025 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) for Dynamics; C III 977 Å, O VI 1032 Å, Ne VIII 770 Å- 3 lines for Waves; C III 977 Å, O VI 1032 Å – 1 or 2 line for 30” Wide Movie
- Observing window preference: High latitude when possible. Perihelion is good for high resolution.
- Other instruments: EUI/FSI and HRI for context imaging; PHI for magnetic field structure; METIS for solar wind mapping.
- 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 (groups of 4 pixels)