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

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

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

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. 6-12 hours ‘Sheeley blobs’; Rouillard et al; Sanchez-Diaz et al.) Indirect (not even from same time) link of Helmet streamer-> HCS structures

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

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

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.

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

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

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

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

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)

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

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

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. 2009 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

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?

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

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

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.