Description of the objective:
Solar observations show that the elemental composition, temperatures and thus the charge states of large coronal loops outside of coronal holes are similar to the composition of the slow solar wind (Feldman et al. 2005; Baker et al., 2013; Brooks et al., 2015). Loop source models require that the foot-points of open field lines are interspersed with large loops outside coronal holes (Fisk et al., 1999; Fisk and Schwadron, 2001). Interchange reconnection between open field lines and loops (along topological boundaries: quasi-separatrix layers, including coronal nulls, e.g. van Driel-Gesztelyi et al., 2012) releases the material stored on the loops and generates the slow wind. Observations indicate the legs or tips of the helmet streamer, loops near active regions, and 80-300 Mm loops may all contribute to the slow wind. The challenge is to associate definitively the features and structures in the slow wind with the morphology of the coronal complex. A loop origin for the slow wind would show sharp interfaces and characteristic variations that can be correlated to the remotely observed sources. Other interesting aspects to be explored include the existence of narrow regions of open field lines between multiple closed field configurations within the streamer belts (Noci et al., 1997; Wang et al., 2000; Noci and Gavryuseva, 2007), slow wind coming from small coronal holes near or inside active regions (Wang, 2017, 10.3847/1538-4357/aa706e) vs from open magnetic flux rooted in active regions (Liewer et al., 2004, 10.1007/s11207-004-1105-z), the differences with the solar activity maximum when the slow wind appears to emanate rather from small coronal holes and active regions (e.g. Neugebauer et al., 2002), the possibility of turbulent reconnection (Rapazzo et al., 2012), the quasi-steady flow from streamer legs (Suess and Nerney, 2006), the transient contribution to the slow wind from parcels of plasma escaping from the streamer core (Suess et al., 2009), explore the sharp interfaces in the slow wind indicative of loop origin, observe the fans at the edge of active regions.
Remarks:
- This objective corresponds to different kinds of structures (helmet streamer, loops near active regions, streamer core, belts, edge of active regions...). These will be different targets observed by the same SOOP.
- As for all solar wind origin objectives, we need to compare the elemental composition, temperatures and charge states of large coronal loops to the in situ slow wind ones (Feldman et al., 2005; Baker et al., 2013; Brooks et al., 2015).
- Several days of observations of a large region surrounding an emerging active region are required, it is probably interesting to observe during a full window for studying the abundance of active regions.
- Observations near the perihelion are preferred for an increased resolution and a higher probability for connectivity.
- For the high-resolution observations, EUI needs to support SPICE with at least one or a few high-resolution frames for each SPICE raster.
- As for all solar wind connectivity objectives, an EMC Quiet period is needed some hours after the remote sensing observations. Note, however, that this is not easy to effectively plan in practice since this would decrease the duration of the remote sensing observation of the active region.
- Parker Solar Probe joint observations at a radial alignment would be beneficial, especially if PSP happens to be at its perihelion.
- Reconnection events at the boundaries of a coronal hole caused by the emergence of a new active region occur on timescales of the order of 1 hr (Rappazzo et al. 2012). Edmondson et al. (2010) also found timescales of the order of 1-2 hr for interchange reconnection processes between an active region loop and an adjacent coronal hole. The typical network supergranule reconfiguration time is of the order of 1-2 days. This timescale can also be adopted as the reconfiguration time of the global magnetic field lines. The magnetic dipole emerging rate in coronal holes is 1-2/day (Abramenko et al. 2006). Schrijver at al. (1998) found that flux concentrations are enhanced and disappear with a characteristic timescale of about 1.5 days. Fisk and Schwadron (2001) state that the characteristic time for a change in the open flux, due to reconnection with loops at low latitudes, is about 36-38 hr. On the other hand, Antiochos et al. (2011) describe the large-scale field evolution as approximated to a sequence of topologically smooth quasi-steady states (quasi-steady models). Therefore we are facing with phenomena occurring on timescales ranging from about 1 hr, if we consider a single active region, to about 36 hr, when we consider the global coronal magnetic field. On this basis, a PHI cadence of 6 hr is enough for investigating interchange reconnection phenomena at a global scale (larger than the active region FoV). A shorter cadence (about 1 hr) might be required to investigate at high spatial resolution interchange reconnection phenomena between an active region and an adjacent coronal hole.
This objective is addressed by the SOOP L_SMALL_HRES_HCAD_Slow-Wind-Connection. The similar SOOP L_SMALL_MRES_MCAD_Connection-Mosaic can be used if we want to cover a wider area around the active region with lower resolution, in particular for the SPICE FoV.
Relevant SOOPs:
L_SMALL_MRES_MCAD_Connection-Mosaic
L_SMALL_HRES_HCAD_Slow-Wind-Connection
L_BOTH_HRES_LCAD_CH-Boundary-Expansion
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van Driel-Gesztelyi et al. 2012:
Rappazzo et al. 2012 (turbulent interchange reconnection):
Quasi-steady flow from streamer legs? (Suess and Nerney, 2006) (should we move this to the streamer blobs section and treat the streamers in one sub-objective whether it is about blobs or legs?)
The model returns values for the flow speed and stream tube geometry (spreading) between the base and a few solar radii. The flow speed is consistent with there being no measurable outflow below 2.5 R and an outflow of 100 km/s at 5 R.
References:
Brooks, D.H., et al., 2015, Full-Sun observations for identifying the source of the slow solar wind, Nature Communications, 6:5947.
Rappazzo, A. F., et al., 2012, Interchange reconnection in a turbulent corona, ApJ, 758, L14.
Suess, S.T. and Nerney, S., 2006, Flow speed inside the brightness boundary of coronal streamers, GRL, 33, L10104.