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In order to construct the current version v0 of the SAP, we implemented the planning strategy described below, by following, step by step, the different presented criteria.

We have to note that the SAP v0 does not include the planning of the Objective 4, even though all the relevant SOOPs have been defined. However many of its sub-objectives are already covered by some of the planned SOOPs. Especially for the strategy of the Objective 4, see 4.0 Overall remarks and feasibility concerning Objective 4 observations with Solar Orbiter. The remarks from that section will be integrated here at the next version.

Criterion 1: Best resolution RS data at different perihelia through the mission

 

We schedule an RS burst SOOP (R_SMALL_HRES_HCAD_RS-burst) whenever we have a perihelion with good telemetry downlink. We could aim at different types of targets or even plain disk centre to discover new physics in Solar Orbiter's highest cadence data, also possibly in unexpected locations.
This campaign would serve several science goals that need very high cadence, need perihelion and are aiming at different types of regions (see SOOP page). Even if off-pointing is not possible, this campaign could still be useful to be run on the Sun-disk centre region. 

The SOOP under consideration is telemetry demanding (see telemetry estimates in SOOP page R_SMALL_HRES_HCAD_RS-burst, 3 to hundreds of times the EID-A rate), so we need good telemetry at the time of the perihelion or right afterwards.

Alternatively, for some science objectives, e.g. 3.2.6 Effects of energetic particles propagating downward in the chromosphere, it may be beneficial to schedule a few short RS bursts into an RS window (or a series of RS windows), to enhance the chances of catching energetic particles (instead of dedicating all telemetry for high-resolution high-cadence observations during a few hours of the window).


Implementation of Criterion 1 for SAP v0:

 

 -> perihelion windows of

For objectives like 3.2.6 Effects of energetic particles propagating downward in the chromosphere, we could possibly try to reserve the best telemetry windows for this case:

 End of the mission may be more restrictive for RS bursts. It is peculiar in the sense that we get many RSW per MTP but in general somewhat lower telemetry downlink:

 - average rate for period 2026-2028 is 1.3 * EIDA rate

 - average rate for period 2026-2029 is 1.64 * EIDArate

Criterion 2: Objectives requiring Metis & SoloHI to observe Earth-directed Transients

 

The CME structure & propagation objectives as well as the blobs objectives ideally need Solar Orbiter and Earth in quadrature with SoloHI looking towards Earth, so Solar Orbiter at GSE -Y.

This criterion can preferably be applied at perihelia but also during high-latitude windows.

Alternatively, instead of quadrature, it will be interesting to observe at 45 degrees separation angle.

SOOPs that are most suitable to run during these times are:

1) L_FULL_HRES_HCAD_Coronal-Dynamics: focussed on the off-limb corona up to Earth 

2) L_FULL_HRES_HCAD_Eruption-Watch: same as above + the solar disk signatures including PHI observing at higher cadence to see CME initiation

The second SOOP is more telemetry demanding but helpful if the CME happens to come towards Solar Orbiter: then it can be viewed sideways from Earth.

Windows that fall close to Equinox could also be preferred since Earth-directed CMEs (and southward IMF SW-Magnetosphere coupling in general) are more geoeffective (Russell and McPherron, 1973).

Other SOOPs that should at least be run few times at quadrature is L_FULL_HRES_MCAD_CME_SEPs and L_FULL_MRES_MCAD_Flare_SEPs (this one with SoloHI towards Earth). Though these can be run at all times, some of its sub-objectives benefit from quadrature with Earth, so that Earth can observe the structure of the CME heading towards Solar Orbiter.


Implementation of Criterion 2 for SAP v0:


This happens at the following perihelion windows:

Also the following RS windows may be interesting, not at quadrature but at 45 degrees separation angle:

MTP 5,7,9 windows happen to fall close to Equinox.

 

Criterion 3: Slow solar wind connection science requiring Earth context for modelling pre-RSW 

We consider 2 very different types of connection science campaigns each requiring different contributions from Earth and modelling:

  1. During solar minimum, the magnetic field configuration is supposed to be quite simple, with slow SW coming from the streamer belt. Also during the early orbits of the mission, Solar Orbiter will stay close to the ecliptic.
    If PHI observes the far side magnetic field in good resolution, and we combine that with the Earth side magnetic field, the full solar magnetic field configuration can be modelled including the location of the HCS that will determine the hemisphere Solar Orbiter will be connected to.
    This model could be the ideal starting point to do a longer term connection SOOP using synoptic data of both IS and RS payload pointed to the most likely connection point.
    During this campaign, PHI keeps on taking regular full disk magnetograms to update the magnetic field model as we go. The modelling should also improve as Earth and Solar Orbiter see overlapping longitude ranges on the Sun.

    Proposed planning strategy:
    • plan during solar minimum (i.e. early in the mission)
    • start with PHI magnetogram data at far side (during one of the higher latitude windows)
    • take some time to construct the model
    • use perihelion extension window to update the model and choose the RS target
    • keep synoptic program during 10-20 days chasing the connection point
    • SOOPs: L_FULL_HRES_LCAD_MagnFieldConfig for the magnetic field modelling (during first RSW), during the connection observations we use L_BOTH_MRES_MCAD_Farside-Connection, possibly combined with L_SMALL_MRES_MCAD_Connection-Mosaic


  2. During the rest of the solar cycle, as the Sun becomes more active, also the magnetic field modelling will become more challenging. In these periods, we hope to rely more on Earth observations to get a well-constrained model of the field that Solar Orbiter is going to fly through. If PHI data are restricted or not available, we mainly rely on Earth to produce the model 4 days in advance due to VSTP turn-around loop. 
    For this to happen, we need Solar Orbiter in the GSE sector X<1 and Y<0, i.e. similar orbits than the ones needed for Earth-directed transients above.
    The further Solar Orbiter moves away from that sector, the more we rely on PHI data to model the most likely connection point. 

    Proposed planning strategy:

Implementation of Criterion 3 for SAP v0:


Case 1 (solar minimum): 

Possible timing: MTP08 - 2022/07/01 - 2023/01/01: PHI observations during South Window (combined with other science goals), connection science during perihelion+North window based on magnetic field model.
(Note that MTP06 - 2021/07/01 - 2022/01/01 is a similar orbit but the first RSW needs to be shifted due to the VGAM. We also do not find more opportunities later in the mission because the Sun will be more active already and so solar minimum conditions will not be met)

 

Case 2 (rest of the solar cycle): 

Possible timing:

Criterion 4: Polar objectives

The different objectives that require high latitude have to be identified (mainly from Objective 4 that is not included in the current version). They have to be planned during high-latitude windows and split between objectives that need good telemetry (for a high telemetry window) and those that they don't.

 

Partial implementation of Criterion 4 for SAP v0:


MTP20-N + MTP21-S good opportunity for detailed pole analysis, telemetry very good for big volume of PHI polar data. SOOPs to be added.

 

Criterion 5: Opportunities for long-term RS observations (concatenated windows or minimal interruption)

 

Some science objectives benefit from a longer period of continuous RS observations, typically in some sort of synoptic mode. A special case of this criterion is RS observations that could run from pole to pole with minimal interruption.

 

Implementation of Criterion 5 for SAP v0:


MTP7 to MTP12 have naturally concatenated RS windows, i.e. 20 days continuous RS window + possible 4 day extension. These MTPs are favourable for L_FULL_LRES_MCAD_Coronal-Synoptic SOOP.

Also MTP13 - 2025/01/01 - 2025/07/01 (EMP) could be used as the 4 day extension window could link 2 RS windows together and give the potential to keep on running (minimal) synoptic observations.

The following MTP periods are even better in the sense that RS observations can run from pole to pole with minimal interruption. This is particularly interesting for L_BOTH_LRES_MCAD_Pole-to-Pole SOOP.

  • MTP11 - 2024/01/01 - 2024/07/01 is particularly interesting because it has 2 sets of concatenated windows. In the 2nd orbit it has only 7 interwindow days between the South window and the extension start of the concatenated period, so you can observe from 9 May to 25 June with minimal interruption. You go from -21º to +21º passing through one of the closest perihelia. 
    telemetry is low in that MTP period which is OK since this SOOP has quite moderate telemetry needs.
  • The 2nd orbit in MTP15 - 2026/01/01 - 2026/07/01 (after VGAM) offers the possibility to observe from 5 May to 19 June with min interruption (few days), flying from pole (31º) to pole through a perihelion windows of 0.3AU!
  • MTP16 - 2026/07/01 - 2027/01/01
  • MTP17 - 2027/01/01 - 2027/07/01 
  • MTP18 - 2027/07/01 - 2028/01/01 - 2nd orbit 

 

Criterion 6: Fast wind connection

 

L_SMALL_HRES_HCAD_Fast-Wind addresses 2 main science goals that in general need coronal holes as a target.

Science objective 1.1.1.1 Low FIP fast wind origins would benefit from a low-latitude (or extended) coronal hole, to increase the chance of connection and to compare the composition of low and fast solar wind streams: this is most likely to happen in the declining phase of the solar cycle (Hathaway: DOI 10.1007/lrsp-2015-4).

We prefer orbits/MTP with a fast scan through a big range of latitudes (like the opportunities above for pole-to-pole SOOP).

 

In particular, in order to address science goal 1.1.1.2 Origin of the small-scale X-ray and UV jets in polar coronal holes, high latitude windows are preferred to ensure the presence of a well-established polar coronal hole that can be observed in full. 
Limb pointing from medium latitude is also interesting to get the Doppler velocity component from SPICE combined with EUI for off-limb intensity. Being up close is a big asset as well!

 

Implementation of Criterion 6 for SAP v0:


For fast wind origins (objective 1.1.1.1)

(we did not add MTP16 because on far side, and did not add MTP11 because of low telemetry)

 

For the goal 1.1.1.2:

Closest high-lat windows are:

  • Any North window from MTP11 to MTP18 gives a good range of latitudes and stays within 0.4AU. 
  • MTP21 - 2029/01/01 - 2029/07/01 - south (up to 31º and 0.38AU) 

Criterion 7: Science objectives needing perihelia but low telemetry requirements

 

L_FULL_MRES_MCAD_Flare_SEPs need medium telemetry downlink. Some of its sub-objectives require quadrature with Earth, so this SOOP is also mentioned above in Criterion 2.

L_IS_STIX needs low telemetry (in practice this SOOP is likely to run throughout all RS windows).

L_SMALL_HRES_MCAD_Suprathermal_Popul needs perihelion for most of its sub-objectives, and off-pointing to a target. telemetry needs are low. -> SOOP still needs review and clean-up. Not yet scheduled in timeline (only 1 of its sub-objectives that need limb pointing).

As the telemetry needs of both SOOPs are moderate to low, we rather schedule at outbound perihelia.

 

Implementation of Criterion 7 for SAP v0:


Criterion 8: Global magnetic field reconstruction & symmetry

 

RS windows at the far side of the Sun should be used to have regular, low cadence imaging of magnetic field, to allow global field reconstruction.

This goal can be addressed by SOOP L_FULL_LRES_MCAD_Coronal-Synoptic or L_FULL_HRES_LCAD_MagnFieldConfig.

Ideally, we plan this SOOP at regular far side windows covering a wide range of phases in the solar cycle.

In addition, the same opportunities will satisfy allow L_FULL_LRES_MCAD_Coronal-Synoptic to address the study of symmetry of the magnetic field and active longitudes (4.2 What are the properties of the magnetic field at high solar latitudes?).

 

Implementation of Criterion 8 for SAP v0:


At first sight, about 7 windows seem to cover these criteria (examples to be added).

 

Criterion 9: Rest of the objectives and special circumstances

 

1.1.2.3 Abundance of minor ions as a function of height in the corona as an indicator of slow or fast wind

will be addressed through SOOP R_SMALL_HRES_LCAD_Composition-vs-Height:

We need limb pointing to address this science goal: either an AR (with open field at the edges) on the limb or the boundary of a streamer, so the target can be chosen at the time of VSTP. We prefer but do not require perihelion. Running this SOOP a bit further out could benefit from Metis participation and enough signal in SPICE. 

Exactly the same requirements are needed for 3.3.1.3 Role of shocks in generating SEPs.

This objective is addressed by SOOP L_SMALL_HRES_MCAD_Suprathermal_Popul and also needs limb pointing at an RS window above 0.55AU, so that Metis can contribute to the observations.

Implementation for SAP v0:


There seem to be plenty opportunities to plan this. Currently, this SOOP has been scheduled in MTPs:

 

 

1.2.1.6 Resolve the geometry of fine elemental loop strands

will be addressed by SOOP R_SMALL_HRES_LCAD_Fine-Scale-Structure.

This needs the highest possible resolution at close perihelia, but no high cadence and thus no particularly high telemetry needs. All close perihelia seem to be candidates for this SOOP.


 

Implementation for SAP v0:

1.1.2.4 Study of density fluctuations in the extended corona as a function of the outflow velocity of the solar wind while evolving in the heliosphere

will be addressed by SOOP R_FULL_HRES_HCAD_Density-Fluctuations. Metis and SoloHI are leading this SOOP.

Telemetry constraints: The SOOP is telemetry limited (less than average) except for Metis that needs more telemetry and SoloHI that seems to need its average allocation. 

This SOOP needs to be repeated at several distances, i.e. each RS window, but not too far out for Metis to still see the density fluctuations (distance limit to be added! 0.5AU TBC). 8 hour per window should be enough.


Implementation for SAP v0:

The ideal orbits to tackle this science objective are the ones with 3 RSW that are quite close to the Sun, e.g. between VGAM 7 and 8 all MTPs have their RS windows within 0.5AU and perihelia at 0.3AU:

These MTPs all happen to fall in EMP. Another option, in the nominal mission, is to schedule this SOOP once in every window of 

  • MTP10 - 2023/07/01 - 2024/01/01 if the option is chosen to move the 3 windows closer together (mainly south window should be moved closer to make it suitable).

Photospheric dynamics (1.1.3.1 and 1.1.4.1.6)

addressed by SOOP R_SMALL_HRES_HCAD_Atmospheric_Dynamics_Structure.

High telemetry needs for EUI, PHI and SPICE during short time (up to 1 hour). We need either perihelion for quiet Sun or close-in high-latitude windows for coronal holes (i.e. North windows).

For perihelion windows, we can select the same ones as for the RS burst above.

 

Implementation for SAP v0:

For perihelion windows, we can select the same ones as for the RS burst above (MTP6, 8, 10, 14, 20).

Closest North windows, with reasonable latitude (>20º), are:

AR dynamics 

SOOP R_SMALL_HRES_HCAD_AR-Dynamics

The best opportunities to study CME initiation and structure (close to the Sun), are to point to ARs at perihelion. We prefer Earth context for modelling and CME context.


 

Implementation for SAP v0:


Earth-sided perihelion or close-in windows (which we interpret at <0.4AU) are:

Opportunities at the edge of 60º angle with Earth are (not added to MTP pages for now):

Most of these opportunities are in EMP which seems OK as we will have more chances for CMEs and dynamic events in general.

 

 

3.2.2 Latitudinal and longitudinal transport of SEPs

SOOP L_FULL_MRES_MCAD_Flare_SEPs (important to have SPP data).

It needs many events, viewed from different viewpoints (also separated from Earth) and different distances. It also needs a range of latitudes (some high-latitude windows as well).

Ideally, it should be scheduled as many periods as possible.


 

Implementation for SAP v0:

The best opportunities are the following, 

  • MTP11 - 2024/01/01 - 2024/07/01- Both Perihelia + NW to have different viewpoints with a range of latitudes and long-term duration (very good telemetry)
  • MTP15 - 2026/01/01 - 2026/07/01- Both Perihelia + NW to have different viewpoints with a range of latitudes and long-term duration (good telemetry)
  • MTP18 - 2027/07/01 - 2028/01/01- Both Perihelia + NW to have different viewpoints with a range of latitudes and long-term duration (bad telemetry in the second Perihelion)

Additionally: MTP14 - 2025/07/01 - 2026/01/01- Perihelion + NW for a range of latitudes and long-term duration (good telemetry) 

 

Energy flux in the lower atmosphere (1.2.1 What mechanisms heat the corona?)

This requires co-observations with Earth-based (DKIST) and NEO (IRIS) facilities, with sets of particular geometries between Solar Orbiter, the target on the Sun, and Earth.


 

Implementation for SAP v0:

Not added to corresponding MTP pages yet

Subject to the resolution requirements (i.e., minimum distance from the Sun) we suggest the following opportunities:

Limb stereoscopy of magnetic fields (5.5.2.1 What are the velocity and magnetic vectors in the solar photosphere?)

This requires perihelion observations at quadrature so that Earth-based/-orbiting assets (specifically the DKIST Fast Solar Polarimeter) can measure the magnetic field from an orthogonal view. R_SMALL_HRES_HCAD_Atmospheric_Dynamics_Structure seems like the best fit for this.

 

Implementation for SAP v0:

Not added to corresponding MTP pages yet


Objectives that could be enhanced with observations from the Parker Solar Probe 

 


Implementation for SAP v0:

The associated opportunities have not yet been defined as they need final trajectory of both Solar Orbiter and Parker Solar Probe. However, the first two SOOPs are scheduled at other opportunities already (based on the other sub-objectives).


 

Objective 4 issues

 

We have to note that during the SAP v0 the Objective 4 has not been planned, even though many of its sub-objectives are already covered by some of the planned SOOPs. Especially for the strategy of the Objective 4, see 4.0 Overall remarks and feasibility concerning Objective 4 observations with Solar Orbiter. The remarks from that section will be integrated here at the next version

Decay of ARs

•Study long-term behavior of active regions (5.5.2.4)
•Capabilities:   near co-rotation, ie. close to the Sun ideally perihelion and close to ecliptic,
SolO as observatory: we would use SOOP R_SMALL_MRES_MCAD_AR_LongTerm including PHI, SPICE and EUI,
we also need stereoscopy: combine solar orbiter data with data from ground based observatories
•Target:   Isolated active region, complex active region close to E limb

Implementation for SAP v0:

Possible target in option E:


Probability distribution functions of the magnetic elements

These observations require a combination of high solar latitude with low heliocentric distance. In the example trajectory, this is often in the third (North) RSW of an orbit. Coordinated observations form Earth-based assets are needed, ideally at a large B0 angle, so close to equinox, particularly September for the North Solar pole/ March for the South Solar Pole. This is challenging.


 

Implementation for SAP v0:

This is challenging, although there is one ideal opporunity in Option E.

SOOP R_SMALL_HRES_HCAD_PDF_Mosaic to be run possibly at following opportunities:

 

Polar observations


  • R_SMALL_HRES_HCAD_Ephemeral would be run on high-latitude patches of quiet Sun or underneath high-latitude coronal holes. As this is looking for variations in the lifecycle of ephemeral regions throughout the cycle (at high latitude), this needs to happen several times throughout the cycle. This will certainly require off-pointing early in the nominal mission, and maybe during the extended mission.

In addition...

Regular polar observations above 15-20 degrees latitude, ideally covering several phases in the solar cycle.

Minimal duration of each campaign is 1 day at cadence 60s for v_LOS at highest resolution (in HRT). Magnetic context once per hour is fine.
Total integrated length should be at least 30 days (more is better, especially for observing cycle variations).

-> each SOOP using PHI in mode 0 can be used to address these goals (SOOPs to be added)

 

Implementation for SAP v0:

Not implemented yet.


Deep focussing

To be scheduled at times when Earth (SDO/HMI) - SC angle lies between 45 and 60 degrees. Run R_FULL_LRES_HCAD_Full-Disk-Helioseismology SOOP during several days (e.g. 3 days).

(FDT at 1 min cadence, only v_LOS.  10-15Mm resolution, i.e. 2x2 binning at perihelion or cropping further out)


Far side imaging for modes passing through the solar core

Would require Earth (SDO/HMI) observations in combination with PHI observations at far side: angle 150 to 210 degrees.

Run R_FULL_LRES_HCAD_Full-Disk-Helioseismology as long as possible, 60 days would be ideal but may not be feasible.

Compression of the images can be quite high (TBC how high).

 


SOOPs that should be running (quasi-)continuously

  • I_DEFAULT -> currently scheduled to run throughout the whole mission. The in-situ instruments will always contribute to this SOOP + may contribute to other SOOPs at the same time (all SOOPs starting with 'L_').
  • L_IS_STIX -> in SAP v0 we scheduled STIX to run throughout all RS windows in its default mode. The STIX data volume downloaded can be steered depending on the available downlink at each time.

 

 

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3 Comments

  1. David Williams

    For reference, the current Solar Cycle prediction I was using was http://solarscience.msfc.nasa.gov/images/ssn_predict_l.gif from http://solarscience.msfc.nasa.gov/predict.shtml .

  2. David Williams

    Low-latitude coronal holes predominantly in the declining phase of the cycle: DOI 10.1007/lrsp-2015-4 

  3. Anonymous

    Hello World! Just checking whether one can comment without an Atlasssian account... can be deleted afterwards. Greetings, Daniel