Reconnection Exhausts Observed by Wind in March 2006

1. Reconnection Exhausts Observed by Wind in March 2006

2. Reconnection Exhausts Observed by Wind in March 2006 V 1-hr avgs. B  

3. Oppositely Directed Exhausts From a Common Reconnection X-Line Similar signatures observed at ACE, Geotail and STEREO B.

4. A Reconnection Exhaust in the Turbulent High-Speed Wind

5. Why is reconnection quasi-stationary? Pressure gradients associated with rarefaction produced by the outflow of plasma from diffusion region sustain reconnection by continually accelerating new plasma and magnetic field into the diffusion region. Why are some reconnection X-lines so long? In 2D (no guide field) short initial X-line expands at significant fraction of Alfven speed (Shay et al.; Lapenta et al.). - Owing to pressure gradient in X-line direction? In presence of strong guide field X-line expansion might proceed at electron thermal speed (Drake, Lapenta: private communication). Not clear why.

6. Results of Survey of 1358 Hours (56.6 Days) of Turbulent, High-Speed (> 600 km/s) Wind Data Only a very small fraction of resolved current sheets contain reconnection exhausts. 34 reconnection exhausts identified (~0.6 events/day). All but 3 of the exhausts were embedded within outward propagating Alfvenic fluctuations. 88% of the exhausts had local widths < 4 x 104 km (~40 ion inertial lengths), corresponding to crossing times < 66s. Local field shear angle, : 26˚ <  < 160˚; <> ~ 90˚. <> ~1.0 85% of  values fall between 0.4 and 2.0. Current sheets and exhausts in turbulent wind have relatively small spatial extents.

7. Simultaneous Wind and ACE Magnetic Field Measurements Spacecraft separation was 7.55 x 105 km, mostly in gse-y direction. ACE and Wind observed different current sheets during this 4-hr interval. Current sheets, and thus also reconnection X-lines, in turbulent high-speed wind are generally far less extensive than in low-speed wind and in ICMEs.

8. The Larger Picture 3-s data - gse coordinates Reconnection is one way by which turbulence is dissipated and the solar wind is heated far from the Sun. Reconnection exhausts observed at a relatively small fraction of all current sheets present in the turbulent, high-speed wind. Questionable if reconnection is a major way by which turbulence is dissipated, but the jury is still out on that.

9. 2D MHD Simulation of Symmetric Undriven Reconnection Courtesy of M. Hesse Note:Reconnection produces a pair of oppositely directed plasma jets. After initialization, reconnection is sustained by flow into rarefaction. The original current sheet becomes bifurcated.

10. Exhaust Widths as a Function of Heliocentric Distance Exhausts narrower than 1-2 x 105 km typically are not resolved by plasma instrument on Ulysses. Exhaust widths do not vary significantly with heliocentric distance. Exhausts broader than ~2 x 106 km have not yet been observed at any heliocentric distance.

11. An Anti-Sunward-Directed Exhaust at the Heliospheric Current Sheet 273 eV electrons Suprathermal Electron Strahl Reconnection occurs at the HCS, but relatively rarely.

12. Strahl Disappearance and An Asymmetric Halo at the HCS: Evidence for Magnetic Disconnection From the Sun Demonstrates magnetic connection across the exhaust and magnetic disconnection from Sun.

13. Oppositely Directed Jets From a Reconnection Site Davis et al. Provides strong confirmation that these events are product of local, quasi-stationary reconnection in solar wind. Confirms presence of strong guide field in many of these events. Dimensionless reconnection rate ~.03.

14. 3 S/C Observations of the 2 Feb. 2002 Exhaust Phan et al. Geometry of the Observations INFER: Reconnection X-line extended at least 390 Re (~2.45 x 106 km). Reconnection persisted for at least 2.5 hours. Extended X-lines and quasi-stationary reconnection are common in solar wind (at least 28 similar events in ACE and Wind data sets).

15. Measurements of X-line lengths and reconnection durations, along with reconnection rates, determine how much magnetic flux is reconnected in an event. Why is reconnection quasi-stationary? Pressure gradients associated with rarefaction produced by the outflow of plasma from diffusion sustain reconnection by continually accelerating new plasma and magnetic field into the diffusion region. Why are X-line lengths so long? In 2D (no guide field) short initial X-line expands at significant fraction of Alfven speed (Shay et al,; Lapenta et al.). In presence of strong guide field X-line expansion might proceed at electron thermal speed (Drake, Lapenta: private communication).

16. Events 2 and 3: A Pair of Roughly Oppositely Directed Reconnection Exhausts Within the ICME and Bounding a Magnetic Filament

17. Simultaneous Wind and ACE Magnetic Field Measurements Spacecraft separation was 7.55 x 105 km, mostly in gse-y direction. ACE and Wind observed different current sheets during this 4-hr interval. Current sheets, and thus also reconnection X-lines, in turbulent high-speed wind are generally far less extensive than in low-speed wind and in ICMEs.

18. Solar Wind Electrons Suprathermal Electron Pitch Angle Distribution 1-D Electron f(v) Vsw = 400 km/s Suprathermal electrons are nearly collisionless and travel 1 AU in ~2-5 hours. They reveal field topology.

19. Measurements of X-line lengths and reconnection durations are important because: They inform us of the overall spatial and temporal scale size of the reconnection process, They contrast with the view that reconnection is fundamentally highly localized in space and time, and 3) Along with reconnection rates, they determine how much magnetic flux is reconnected in an event.

20. S/C Geometry and Heliospheric Environment of the 11 March 2007 Event ACE Reconnection Exhaust STEREO A and B were separated by 1215 Re.

21. Reconnection Exhausts and the Local Magnetic Shear and External Proton Beta Reconnection in solar wind occurs almost exclusively in low beta plasma. Indicates guide field reconnection is common.

22. Some Statistics From the First 49 Exhausts Identified in the ACE data Many of the events observed in association with ICMEs. Only a few events identified at the HCS.

23. Exhaust Encounters Along Ulysses’ Orbit Reconnection exhausts have been identified at all heliocentric distances and latitudes sampled by Ulysses (and Helios), but only once within high-speed streams from coronal holes.

24. Environment Surrounding a Brief Accelerated Flow Event in the Solar Wind ACE 272 eV Pitch Angle Distribution A brief interval of accelerated flow (red arrows) was associated with a large field shear separating distinctly different plasma regimes. It probably occurred at the interface between two ICMEs. Many, but certainly not all, such brief accelerated flow events are associated with ICMEs.

25. Magnetic Field and Flow Velocity Changes Associated with the 23 November 1997 Event The accelerated flow filled a large (149˚) change in field orientation. The current sheet was bifurcated with an intermediate field orientation in the center. V,B changes were anticorrelated at leading edge and correlated at trailing edge of exhaust. Thus the accelerated flow was bounded by Alfven waves propagating antisunward in opposite directions along B. This is the characteristic signature by which we identify reconnection exhausts in the solar wind.

26. Other Aspects of the 23 November 1997 Event Exhaust The plasma states on opposite sides of the event were distinctly different, but both were characterized by low proton beta. Overall transitions from outside to inside the exhaust were slow-mode-like on both sides. (Exceptions occur in some events and not true in general for electrons.) We have now identified more than 250 accelerated flow events of this same general nature in ACE, Ulysses, Helios and Wind solar wind data.

27. Details of the 2 Feb. 2002 Reconnection Exhaust at Wind in Boundary Normal Coordinates Phan et al. Flow speed change agreed with Walen condition. Change in normal speed ~5 km/s. Implies Vin ~ 2.5 km/s and low reconnection rate. Reconnection was not obviously driven by the external flow (a general result).

28. An Expanded View of the 10/3/2000 Reconnection Exhaust Exhaust The large proton temperature and temperature anisotropy was associated with interpenetrating beams along B. Reconnection exhausts typically occur at relatively large shears in B separating solar wind regions having distinctly different plasma and field conditions but always having low proton beta.

29. Reconnection Exhausts in the Solar Wind Exhaust 2D projection A reconnection jet or exhaust is identified as roughly Alfvenic accelerated plasma confined to a field reversal region. Current sheet is typically bifurcated (double step). Changes in V and B are anti-correlated at one edge and correlated at the other, indicates Alfven waves propagating in opposite directions along reconnected field lines.

33. Counterstreaming Suprathermal Electrons and CMEs in the Solar Wind

34. An Anti-Sunward-Directed Exhaust at the Heliospheric Current Sheet Suprathermal Electron Strahl Reconnection occurs only rarely at the HCS.