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Description of the objective:

  • Trace streamer blobs ("helmet streamer plasmoids") and other structures through the outer corona and the heliosphere (Sheeley and Rouillard, 2010).
  • Study periodic density structures (Viall and Vourlidas, 2015) in the low corona and for different times in the solar cycle.

The helmet streamer plasmoids are:

  • observed in white light images as the continual, episodic releases of plasma from the tips of helmet streamers
  • also observed in situ at 1 AU and tracked from the upper corona to 1 AU (swept up and compressed by the fast solar wind from low latitude coronal holes) (Sheeley and Rouillard, 2010). 
  • small interplanetary transients (size of 0.05-0.12 AU, magnetic field rotation between 2 and 13 hours) can be traced back to streamer events, but also to CMEs (Rouillard et al., 2011)
  • flux ropes (Sheeley et al., 2009; Rouillard et al., 2011)
  • exclusively plasma sheet phenomena (Wang et al., 2000)
  • rate of ~4/day or approximately every 6 hours
  • large in scale, initial sizes about 1 Rs in the radial direction and 0.1 Rs in the transverse direction (Sheeley et al., 1997)
  • originate at about 3-4 Rs (Sheeley et al., 1997)
  • speeds: 150 km/s at 5 Rs, 300 km/s at 25 Rs
  • thought to be released through either interchange reconnection, and/or complete disconnection, and in either case, the reconnection takes place at high altitudes (Wang et al. 2000; Zurbuchen 2001; Crooker et al. 2004; Suess et al. 2009).


Other periodic density structures are:

  • often not flux ropes (Viall et al., 2009)
  • observed in 70%-80% of the slow solar wind and in much of the ecliptic fast wind (Viall et al., 2008)
  • rates of several minutes, characteristic timescale of 90 minutes, with a range of 65-100 minutes (Viall and Vourlidas, 2015)
  • small scales (70-3000Mm) 
  • largest scale structures often contain smaller ones embedded within them (Viall et al., 2010)
  • always associated with streamers and the HCS (Viall and Vourlidas, 2015)
  • formed at or below 2.5 Rs, no evidence of formation above these heights (Viall and Vourlidas, 2015).

 

Remarks:

 

  • In general, not easy to distinguish radial vs transverse scales of structures. Joint observations with PSP will be very important.
  • At least one perihelion would be required for this objective for looking at the birth of the structures. METIS would better observe from 0.3-0.35 during a zooming-out (North) window.
  • Low-latitude preferred.
  • Minimum activity preferred, but the maximum could also be interesting if we could manage to disentangle other effects.
  • For linkage science, we would need Earth in quadrature and either observe in situ on Solar Orbiter what Earth sees or observe in situ at 1 AU what SoloHI sees. For SoloHI to be useful, we need a GSE –Y quadrature.
  • The SoloHI turbulence mode should be used at perihelion for looking at the formation, acceleration, shape, and evolution of the fastest periodic structures. For making sure that we will see at least one blob at its birth (frequency of 1 every 6 hours), the turbulence mode (20 sec) should be used for approximately 12 hours (or 1 day).

 

 

This objective is addressed by the SOOP  L_FULL_HRES_HCAD_Coronal-Dynamics, which is aimed at observing structures in the outer corona and linking them to the heliosphere observed in situ. METIS and SPICE are leading this SOOP, while in situ payload provides continuous observations. Synoptic support from other remote sensing instruments is provided. Disk center pointing is preferred.

Other SOOPs are partially addressing the connectivity aspects of the objective (but not the formation and evolution of the fastest structures). These are L_SMALL_MRES_MCAD_Connection-Mosaic, L_SMALL_HRES_HCAD_Slow-Wind-ConnectionL_BOTH_MRES_MCAD_Farside-Connection

 

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Helmet streamer plasmoids are:

  • observed in white light images as the continual, episodic releases of plasma from the tips of helmet streamers
  • also observed in situ at 1 AU and tracked from the upper corona to 1 AU (swept up and compressed by the fast solar wind from low latitude coronal holes) (Sheeley and Rouillard, 2010). 
  • small interplanetary transients (size of 0.05-0.12 AU, magnetic field rotation between 2 and 13 hours) can be traced back to streamer events, but also to CMEs (Rouillard et al., 2011)
  • flux ropes (Sheeley et al., 2009; Rouillard et al., 2011)
  • exclusively plasma sheet phenomena (Wang et al., 2000)
  • rate of ~4/day or approximately every 6 hours
  • large in scale, initial sizes about 1 Rs in the radial direction and 0.1 Rs in the transverse direction (Sheeley et al., 1997)
  • originate at about 3-4 Rs (Sheeley et al., 1997).
  • speeds: 150 km/s at 5 Rs, 300 km/s at 25 Rs
  • thought to be released through either interchange reconnection, and/or complete disconnection, and in either case, the reconnection takes place at high altitudes (Wang et al. 2000; Zurbuchen 2001; Crooker et al. 2004; Suess et al. 2009)

 

       (Sheeley et al., 1997)

 

 

Periodic density structures are:

  • often not flux ropes (Viall et al., 2009)
  • observed in 70%-80% of the slow solar wind and in much of the ecliptic fast wind (Viall et al., 2008)
  • rates of several minutes, characteristic timescale of 90 minutes, with a range of 65-100 minutes (Viall and Vourlidas, 2015)
  • small scales (70-3000Mm) 
  • largest scale structures often contain smaller ones embedded within them (Viall et al., 2010)
  • always associated with streamers and the HCS (Viall and Vourlidas, 2015)
  • formed at or below 2.5 Rs, no evidence of formation above these heights (Viall and Vourlidas, 2015)

 

 

 

  • SPICE
      • Target: Coronal holes and coronal hole boundaries.
      • Observing mode: Composition mapping (to derive both FIP maps and Doppler velocity maps in a wide region which include possibly both the coronal hole and its boundary)
      • Slit:  6”
      • Exposure time/cadence and number of X positions:  180 s, X=160
      • Field of View: 16’×11’
      • Number of repetitions of the study: 1
      • Observation time: 8 hours
      • Key SPICE lines to be included: 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)
      • Observing window preference: Low latitude preferred.
      • Other instruments: EUI for context, PHI, METIS, SWA and MAG
      • 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.

 

References:

 

Rouillard et al., 2011, The solar origin of small interplanetary transients, ApJ, 734, 7.

Sheeley and Rouillard, 2010, Tracking streamer blobs into the heliosphere, ApJ, 715, 300.

Sheeley et al., 2009, The structure of streamer blobs, ApJ, 694, 1471.

Sheeley et al., 1997, Measurements of flow speeds in the corona between 2 and 30 Rs, ApJ, 484, 472.

Viall et al., 2009, GRL, 36, L23102.

Viall et al., 2008, JGR, 113, A07101.

Viall et al., 2010, Sol. Phys., 261, 175.

Viall, N.M., and Vourlidas, A., 2015, Periodic density structures and the origin of the slow solar wind, ApJ, 807, 176.

Wang Y.-M. and Sheeley N. R., 2006, Observations of flux rope formation in the outer corona, ApJ, 650, 1172.