1. Understanding the Origin of the Slow Solar Wind by Linking Remote and In Situ Observations
Nicholeen Viall
NASA/GSFC
In collaboration with : Larry Kepko, Spiro Antiochos, Sue Lepri, Angelos Vourlidas, and Jon Linker

2. Connecting the Sun to the Heliosphere
August 1, 2008
Pseudostreamer and helmet streamer
Which solar structures become structures in the Heliosphere?
Success with large-scale (e.g. CIRs; CMEs), but not for smaller-scales

3. Success indirectly linking solar structures to heliosphere (in situ) on smaller scales
~tens of minutes up to a few hours
~100 Mm up to a few thousand Mm radial length scale
‘small’ – compared to current heliospheric imager resolution and in situ composition measurements
‘large’ – compared to turbulence (energy containing scales) and Earth’s magnetosphere/space weather
I’m going to talk about some
Solar Orbiter will finally give a DIRECT link of these smaller scale sizes

4. Connecting helmet streamer structures and in situ structures in the Heliospheric Current Sheet
In situ at 1 AU
Viall & Vourlidas 2015
Kepko, Viall, Antiochos, Lepri,
Kasper, Weberg 2016
Left –STEREO images of helmet streamers creating density structures; FFTs show a characteristic ~90 minute timescale
Helmet streamers have long been known to be highly dynamic (e.g hours ‘Sheeley blobs’; Rouillard et al; Sanchez-Diaz et al.)
Indirect (not even from same time) link of Helmet streamer-> HCS structures

5. Flying Through a Train of Density Structures
Heat flux shows Heliospheric current sheet (HCS) crossing
Proton density changes coincide with changes in alphas, C, O, charge state (no V change) – solar origin
Specially processed, high time resolution ACE composition; typical resolution averages over these structures, and leads to incorrect interpretation of ‘steady’ slow solar wind
We observed perdiocid density structures in situ
Note ‘periodic’ = characteristic time scale, these are not waves
Kepko, Viall, Antiochos, Lepri,
Kasper, Weberg 2016

6. Flying Through a Train of Density Structures
Heat flux (strahl) and B field changes associated with structures (one structure in the train is a flux rope!) this indicates magnetic reconnection (S-web)
HCS are well known to contain structures created through magnetic reconnection (Crooker; Suess; Rouillard)
We observed perdiocid density structures in situ
Note ‘periodic’ = characteristic time scale, these are not waves

7. Is the HCS/Helmet streamer a special boundary where solar wind transients are injected into an otherwise steady solar wind?
S-web says there are other locations
Our previous in situ solar wind work says there are other locations [Viall et al. 2008]
We set our undergrad summer interns loose to find solar wind structures with composition signatures that were NOT at the HCS
We see periodic proton density structures in 70-80% of slow solar wind, suggesting that such structures are a substantial component of the ssw. If this is true, then we should see proton density structures (with compositional changes confirming solar source) not only at the HCS crossing, but other places as well.

8. PFSS as viewed by STEREO A
August 2008
HCS is aimed south of Earth; pseudostreamer is aimed north
PFSS as viewed by STEREO A
That eclipse image from first slide and spiro

9. Images and in situ data show pseudostreamer continually releases ‘blobs’, ‘puffs’ and structured solar wind
Still circumstantial; indirect

10. HI1 images show pseudostreamer continually releases ‘blobs’, ‘puffs’ and transient solar wind structures
DeForest processed HI1 – on STEREO/SECCHI webpage

11. 250 km/s (Faster ones are 400 km/s)
Time-distance plots show continuous release of transient structures from pseudostreamer
250 km/s (Faster ones are 400 km/s)
Like Jmaps

12. 250 km/s (Faster ones are 400 km/s)
Time-distance plots show continuous release of structures from pseudostreamer
250 km/s (Faster ones are 400 km/s)

13. In situ, Wind/ACE observe a stream interface, many slow
In situ, Wind/ACE observe a stream interface, many slow wind structures, and no HCS
Ace C & O
Ace C6+/C5+ Charge State
14 days without a HCS
Slow wind shows highly structured proton density, alpha, carbon, oxygen, charge state - solar source
T sector
A sector
Two traces are 3DP and SWE

14. Two-day zoom-in shows series of ~2.5 hour structures
Alphas and C and O track one another with similar ~2.5 hr variation: structures are from solar source
Typical hour cadence would have lead to false conclusion of steady solar wind
Define boundaries based on compositional changes

15. Magnetic reconnection releases coronal loops with different heating histories
Composition boundaries generally correspond to B field tangential discontinuities and rotations, but not in a predictable orientation/way [see also Viall et al alpha event]
Two heat flux drop outs in the train of periodic density structures are signs of connectivity changes to very long field lines (e.g. through interchange rxn to flux ropes; Chollet et al. Pagel et al)
Laming talk

16. PFSS as viewed by STEREO A
Images and PFSS show HCS is depressed and aimed south of Earth; pseudostreamer directed north of Earth
PFSS as viewed by STEREO A
So what exactly are we mapped to at 1 AU?

17. In situ Event Maps to Complex S-web Arcs
Predictive Science Inc

18. Conclusions
Images show helmet streamer and pseudostreamer are highly dynamic, continuously producing slow wind ‘blobs’, ‘puffs’ and structures
In situ observation of highly structured slow solar wind at 1 AU from S-web arc and helmet streamer
Structure in proton density, alpha, carbon, oxygen, charge state, and B, but NOT velocity is a test on all models of slow solar wind
Solar structures -> in situ structures
Magnetic reconnection necessary; something like reconnection at the S-web is needed to explain observations

19. Prediction for Solar Orbiter: There is no such thing as ‘the steady solar wind’
No such thing as steady solar wind, just like in magnetosphere they learned (with better data) that there is no such thing as steady magnetospheric convection. Magnetic fields always store and then release energy.
Solar orbiter will finally be able to make DIRECT link between solar source and heliospheric structures
Key is to get high time resolution composition + modeling
Crooker et al.