Description of the objective:


One of the biggest discoveries of the Hinode satellite is the frequent occurrence of small-scale X-ray and UV jets in polar coronal holes (Cirtain et al. 2007; Nistico et al., 2009; Krucker et al., 2011). Such jets have widths between 2 × 103 and 2 × 104 km. Their origin is thought to be magnetic reconnection of coronal field lines. At the reconnection site, Alfvén waves develop and produce outflow velocities up to 800 kms-1, while the energy released by the reconnection heats the plasma locally, generating mass motions with sonic speeds of ∼200 kms-1.

Given the high velocities and frequency of these events, it has been suggested that they contribute to the fast solar wind. Their relations to the photospheric magnetic field, or the relevance of photospheric processes for triggering them, have not been established yet. The high latitudes at which they are observed hamper the accurate determination of their photospheric footpoints either from the ground or NEO. Observations with remote-sensing instruments aboard Solar Orbiter will allow us to understand the relation of these jets from a unique vantage point, providing comparable high-angular resolution data simultaneously in the corona, chromosphere, and photosphere. 

Remarks:

This objective could also be considered as part of the previous one (1.1.1.1). It only appears in a separate section because it mostly requires remote sensing observations including STIX. From the operational point of view, it can be jointly addressed with 1.1.1.1 with the SOOP L_SMALL_HRES_HCAD_Fast-Wind. Observation of a sufficiently extended coronal hole is required in order to catch multiple jets.

Relevant SOOPs:

L_SMALL_HRES_HCAD_Fast-Wind 

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Required observations:

  • SPICE (updated by Alessandra Giunta 01/12/2015): 
    • Target: Polar coronal holes
    • Observing mode: Dynamics
    • Slit: 4'' or 2''
    • Exposure time/cadence and number of X positions: 10 s, X=128
    • Field of View: 8'x11' or 4'x11'
    • Number of repetitions of the study: Up to 30
    • Observation time: Up to 10.9 hours (0.4 hours per study)
    • 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) – 4 profiles and 6 intensities
    • Observing window preference: High latitude observing is ideal for polar coronal holes. Perihelion also goodifcoronalholehasequatorialextension.
    • Other instruments: EUI for context imaging; PHI for magnetic field structure of jet bright points; STIX for high-energy signatures; EPD for the detection of high energy particles
    • 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.

      -It will not be possible to target an individual bright point, so SPICE will have to rapidly scan a large field-of-view for performing statistical studies of jets. Coronal hole jets reach about 1.5 MK (from EIS), with bright points around 2 MK. Another option is to use the 30” to scan the FOV in about 3-5 mins to allow multiple snapshots of jets (lifetimes about 10-15 mins).

      - Possible binning on Y direction (groups of 4 pixels)