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Welcome
• Purpose: – To facilitate interaction among colleagues in
space science in the New England Area (UNH, SAO/CfA, BU, MIT, Hanscom/AFRL, Haystack, Dartmouth )
– To leverage these interactions for initiating new, cross-disciplinary and far-reaching projects
• Meetings:– quarterly meetings
• Introductions (Affiliation/Interest)
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Questions• To what extent can reconnection account for heating otherwise
attributed to turbulent dissipation in the solar wind?• To what extent is the rate of reconnection controlled by macroscopic
boundary conditions as opposed to kinetic-scale processes?• To what extent do observations of reconnection in the solar wind bear
upon the issue of coronal heating?• To what extent does quasi-steady reconnection occur in the
magnetosphere and the solar atmosphere?• Does reconnection necessarily produce particle (as opposed to plasma)
acceleration? If not, why not• In what essential ways is guide field reconnection fundamentally
different from anti-parallel reconnection?• What causes extended X-lines?• What distinguishes "explosive" reconnection?• Why does reconnection prefer low plasma beta?
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Discussion
• To what extent can reconnection account for heating otherwise attributed to turbulent dissipation in the solar wind?
• To what extent do observations of reconnection in the solar wind bear upon the issue of coronal heating?– How do observed events contribute to a heting rate?– We are not seeing all the events?– The finer the data, the more events are found (but are they
real reconnection events)– What heating rate do we need? (couple times 10^3 J/(kg s)– High speed wind heated more than slow wind (Vasquez
paper , 2007)– DO all the particles find their way to the current sheet
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Discussion
• Run S/C through simulations to see how they compare to observations
• How much of the heating occurs at unresolvable scales?
• We are within an order magnitude of the observational scales we need to resolve the recon. Structures– Rapid plasma measurements on the oder
of the gyrofrequency (convected) .. 10 Hz?
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Discussion• Relation of outward/inward propagating modes• Fast wind mostly outward propagating .. This may partially
explain why we see fewer rec. events in fast wind• Braiding• Most of the discontinuities/current sheets are not
reconnecting– Is it possible we see current sheets, but not the exhaust– What is the length of the diffusion region
• What is special about the reconnection events we observe– Beta is important (beta typically low in reconnection events)
• What do we know about the rate at which reconnection proceeds from the Sun– Is fast wind just less evolved
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Discussion
• Tpar larger than Tper in exhaust• Slowing of the jet gives rise to heating• Evidence of wave-particle interaction
(resonance .. Higher Tper) in the corona condradicts heating from reconnection
• Rate of holes rises exponentially below beta = 1 (firehose instability may play a limiting role for beta > 1)
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Discussion
• How does reconnection in the solar wind bear upon reconnection in the corona?– Steps: current sheets occur in closed fields
• 5-10 Rs .. How important are current sheets there
– Borovsky structures in solar wind appear to be related to source structure (granulation/supergranulation) .. Or is this in situ development .. Fossil coronal structure
– Do we see source structures from the Sun– How can we connect them?
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Discussion
• Is the rate of reconnection set by the micro or macrophysics? (which is the dog and which is the tail?)– What determines the explosiveness of the
event?– What controls the intermitence?– Length of the current sheet is a telling
factor– Both macro and microphysics contribute to
setting the timescale (rate) of reconnection
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Discussion
• CME - plasmoid comparison demonstrates that the onset scenario can operate in different regimes– Comparison of length scales (ion intertial, plasma
and gyroradii are very different)– The similarity of phenomena (plasmoids,
Supraarchade downflows, bursty bulk flows) suggests that the driving conditions are fundamental to the overall response of the conditions
– Tearing mode instability (enhanced) may be key
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Discussion
• Thermal Electrons do not show evidence of heating in the diffusion region [Egdal]. This is consistent with Jack’s observations
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Discussion
• Is reconnection always bursty .. Or can it be steady? [Forbes]– Gosling has shown us a lot of steady reconnection
events– Flux Transfer Events non-steady [1 every 8 minutes]– Bursty Bulk Flows non-steady– Is the burstyness controlled by variability in the
driving or the microphysics?– Takes an Aflven wave about 10 hours to move
along an observed X-line [6 Rs .. Va ~ 50 km/s]– Is reconnection inherently patchy? Global
reconnection rate sum over patches• Jack believes the answer is no
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Looking Forward
• Multi-spacecraft studies• What are the possibilities for imaging?• Can we make more of our existing
observations– Theory and observations .. Bringing these
together more tightly
• Instrumentation capable of higher resolution measurements .. Electrons, ions, composition
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Today’s Agenda
– 11-11:15 congregate– 11:15-12:15 Reconnection Observed:
Gosling– 12:15-1:30 Lunch– 1:30-3 PM Panel Discussion – 3- 5 PM Informal Discussion/Meeting
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