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The Structure of the HPS
The in situ Density Story Nicholeen Viall NASA GSFC
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Streamers Continuously Produce Periodic Density Structures
Viall & Vourlidas 2015 Viall et al. 2010 Streamers are highly dynamic, creating density variability in the form of periodic density structures Characteristic Periodicity ~ 90 minutes; Characteristic sizes ~ 1000 Mm Seen further out in HI1 too In situ they occur all the time (70% to 80% of slow solar wind, Viall et al. 2008) At May SPP SWG, showed density structures associate with helmet streamers (SECCHI images) and at the HCS (in situ Wind/Ace)
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Flying Through a Train of Periodic Density Structures
HSC crossing filled with train of ~90 minute periodic density structures Velocity ~constant Alphas, C, O, charge state and B (classic flux rope!) together indicate magnetic reconnection (S-web) in solar corona created these structures Kepko, Viall, Antiochos, Lepri, Kasper 2016
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We set our undergrad summer interns loose to find density structures with composition signatures that were NOT at the HCS
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Wind/ACE see SI and periodic density structures with no HCS
Towards sector Away sector Interesting proton density structures Aug Well separated from SI Velocity constant at ~320 km/s 14 days without a HCS
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Two-day Zoom-in on Periodic Density Structures
Multi-scale event ~12 hour proton enhancements anticorrelated with a ~12 hour alpha enhancement ~3 hour periodic density structures with alpha composition signatures
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Use STEREO to Piece Together 3-D Picture and ID Solar Source
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STEREO B sees ~3 hr periodic density structures at (rotationally adjusted) same time as Wind/ACE
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STEREO A ALSO sees periodic density structures at (rotationally adjusted) same time as Wind/ACE
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Solar source (not at the HCS) continuously released density structures for at least 6 days
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Look to The Sun ~ 5 days Prior
Closest to viewing Earth-Sun line Helmet streamer is depressed, consistent with no HCS crossing
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PFSS as viewed by STEREO A
PFSS confirms HCS is depressed and aimed south of Earth PFSS as viewed by STEREO A PFSS as viewed by STEREO B Closest to viewing Earth-Sun line
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Neither helmet streamer nor Pseudostreamer plasma directed towards ecliptic
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Antiochos et al. 2011 Periodic Density Structures Stream Interface
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Highly variable/structured slow solar wind density at 1 AU; characteristic plasma release ~ a few hours Alpha composition signatures confirming solar source of variability Solar source of periodic density variability persists for at least 6 days Neither helmet streamer/HCS nor pseudostreamer seems to be the source… Need full 3-D topology (e.g. reconnection at S-web corridors) to explain Immediate Future: High res ACE composition from Sue; statistics on SECCHI periodicities from pseudostreamer and helmet streamer at that time SPP Future: These structures ~1000 Mm too small to follow in imagers from release to S/C impact. Will see rxn.
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30 Minute Periodic Density Structures with Alpha/Proton Abundance Ratio Changes
a) A clear 30-minute (~850 Mm) periodic number density structure b) Detrended time series to identify more clearly the 30-minute periodicity - they are in anti-phase (no ACE yet) Viall et al., 2009
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