Z.Y. Pu, Z.Y. Pu, J. Wang, X.G. Zhang, Q.G. Zong, S.Y. Fu, L. Xie, J. Wang, X.G. Zhang, Q.G. Zong, S.Y. Fu, L. Xie, C.J. Xiao, X.G. Wang C.J. Xiao, X.G. Wang (Peking University, China)(Peking University, China)

M.W. Dunlop (M.W. Dunlop (Space Sciences Division, RAL, Oxford, UKSpace Sciences Division, RAL, Oxford, UK)) P. Escoubet (P. Escoubet (ESA/ESTEC, Noordwijk, NetherlandsESA/ESTEC, Noordwijk, Netherlands))

Magnetic Reconnection Magnetic Reconnection at the Magnetopause: at the Magnetopause:

New Results from Double Star New Results from Double Star & Cluster Observations& Cluster Observations

● New results of magnetic reconnection New results of magnetic reconnection (MR) from Double Star & Cluster (MR) from Double Star & Cluster observations observations ● SummarySummary

● IntroductionIntroduction

OutlineOutline

1. Introduction1. Introduction

Magnetic Reconnection Magnetic Reconnection (MR)(MR)

MR is a fundamental process in plasmas by MR is a fundamental process in plasmas by which the B field topology changes and which the B field topology changes and connections of particles with the field are re-connections of particles with the field are re-arranged. arranged. MR is the major process responsible MR is the major process responsible for energy transport in space plasmas.for energy transport in space plasmas.

X-line-

MR at the Magnetopause (MP)MR at the Magnetopause (MP)Dungey (1961,1963)Dungey (1961,1963)

IMF southwardIMF southward

IMF northwardIMF northward

★

★

★

Observations of Quasi-Steady and Observations of Quasi-Steady and Transient MR at the Transient MR at the MP MP

● ISEE 1/2 detected quasi-steady MR at the ISEE 1/2 detected quasi-steady MR at the dayside MPdayside MP (Paschmann et al. 1979)(Paschmann et al. 1979)● ISEE 1/2 & HEOS-2 identified impulsive MR ISEE 1/2 & HEOS-2 identified impulsive MR (FTEs) (FTEs) (Russell & Elphic, 1978; Haerendel et al. 1978)(Russell & Elphic, 1978; Haerendel et al. 1978)

quasi-steady MR quasi-steady MR Flux transfer events (FTEsFlux transfer events (FTEs))

X-line-

Importance of MR at Importance of MR at thethe MP MP

MR at the MP is the major mechanism MR at the MP is the major mechanism responsible for the solar wind eresponsible for the solar wind energy, nergy, plasma and magnetic flux transports into plasma and magnetic flux transports into the magnetosphere.the magnetosphere.

Outstanding QuestionsOutstanding QuestionsBefore launching of Double Star (DS), there Before launching of Double Star (DS), there were ongoing debates and studies on a were ongoing debates and studies on a number of outstanding problems. DS-Cluster number of outstanding problems. DS-Cluster coordinated measurements provide a unique coordinated measurements provide a unique opportunity to study these key questions.opportunity to study these key questions.

Cluster

TC-1

●●Anti-Parallel vs Component MR?Anti-Parallel vs Component MR? Where MR is initiated at the dayside MPWhere MR is initiated at the dayside MP? Anti-parallel ? Anti-parallel MR at high-latitude, or component MR near the sub-solar MR at high-latitude, or component MR near the sub-solar point?point? ( (e.g., e.g., Karimabadi et al., 2005; Trattner et al., 2005))

Some observations were in favor of the former, others Some observations were in favor of the former, others agreeed more with the latter agreeed more with the latter (e.g., (e.g., Petrinec et al., 2004; Petrinec et al., 2004; Retino` et al., 2005; ; Kim et al., 2002; Chisham et al., 1999)

anti-parallel MR Component MR (Crokker,1979; Luhmann et (Crokker,1979; Luhmann et al., 1984)al., 1984)

((Gonzalez and Mozer, 1974; Gonzalez and Mozer, 1974; Sonnerup, 1974; Cowley, 1976)Sonnerup, 1974; Cowley, 1976)

IMF

● Global Global ConfigurationConfiguration of the X- of the X-Line at the MP ?Line at the MP ?

Moore & Fox Moore & Fox (2002)(2002)

X-lineA Null

●

●

B Null

Law and Finn Law and Finn (1990)(1990) Wang Wang (1996)(1996)

Various global patterns were suggested based on Various global patterns were suggested based on modeling, theoretical and observational studies modeling, theoretical and observational studies

Fuselier et Fuselier et al.(2002)al.(2002)

X-lines

●● Global View of Global View of Formation and Formation and Motion of FTEs ?Motion of FTEs ?

(From Owen et al(From Owen et al.)Paschmann (2002)Paschmann (2002)

Magnetosheath(MSH)

Magnetosphere(MSP)

Double Star MissionDouble Star Mission

Double StarDouble Star TC-1was TC-1was launched into an orbit launched into an orbit of 570 km of 570 km 13.4 R13.4 REE, , inclined at 28.5inclined at 28.5oo. .

Conjunctions between Cluster Conjunctions between Cluster and Double Starand Double Star

Cluster

TC1

During Jan. to April, Cluster and TC-1 During Jan. to April, Cluster and TC-1 have apogees in dayside solar wind, have apogees in dayside solar wind, suitable for coordinated observations of suitable for coordinated observations of MR at the dayside MP. MR at the dayside MP.

II. New results of MR from Double II. New results of MR from Double Star & Cluster observations Star & Cluster observations ● Convincing in situ evidence for component Convincing in situ evidence for component MR near the sub-solar poiMR near the sub-solar point nt (IMF B(IMF Byy 0) 0) ● Simultaneous occurrence of Simultaneous occurrence of anti-parallel and anti-parallel and component MR under similar IMF conditions component MR under similar IMF conditions (IMF B(IMF Byy 0) 0) ● Global extent & Global extent & configurationconfiguration of the X-Line at the MPof the X-Line at the MP●● Global view of Global view of formation formation and motion of FTEs and motion of FTEs

Data ProcessingData Processing Vjet = Vobserved – Vbackground

Definition of Vbackground

Criterion of event selectionCriterion of event selection::|V|Vjetjet| > 250 km/s| > 250 km/s

Duration > 30 sDuration > 30 sRelatively steady IMF clock angleRelatively steady IMF clock angle

(Pu et al. 2007)

(Zhang, 2007) More than 1500 events were selected

Event Selection & MR Site Event Selection & MR Site DeterminationDetermination

BN

BN

VVLL & B & BNN reversals reversals Walen testWalen test

Hall effect Hall effect (Oieroset et al., 2001)(Oieroset et al., 2001) Plasma mixing Plasma mixing (Zhang, 2007)(Zhang, 2007)

(Paschmann, (Paschmann, 2002)2002)

Criteria for Component MRCriteria for Component MR

BSP

BSH

y

z

Three types for Component MR : (1) Three types for Component MR : (1) the shear angle the shear angle across the local MP at the MR siteacross the local MP at the MR site is noticeably < 180is noticeably < 180oo ; ; (2) (2) a guide field is present inside the a guide field is present inside the diffusion region; (3) diffusion region; (3) The The IMF BIMF Bzz in the adjacent magnetosheath in the adjacent magnetosheath is positive.is positive.

0o

180o

● Convincing In Situ Evidence for Convincing In Situ Evidence for Component MR Near the Sub-Solar PointComponent MR Near the Sub-Solar Point

Bx0

60

0

1

110

10

100

-100

40 BzBy

N

T

VyVz

MTH MSP

MP

Shear Angle

Sheath

20

-20

Vx

◆ ◆ Case studies: Case studies: Component MR Component MR on 2004-03-26 on 2004-03-26 TC-1 at ~(10.4, -2.2, -1.4) RTC-1 at ~(10.4, -2.2, -1.4) REE; ; IMF BIMF Bzz >0; Shear angle ~60 >0; Shear angle ~60oo

Sphere

(Pu et al. 2005a)(Pu et al. 2005a) 09:46:20-09:47:3009:46:20-09:47:30 UTUT 09:41:00-09:43:55 UT09:41:00-09:43:55 UT

C=0.9502 C=0.9768

Y=-0.74X+4.84 Y=-0.82X+2.84

Flow reversal

““the direction of the flows, the direction of the flows, northerly (southerly) for TC-1 northerly (southerly) for TC-1 locations north (south) of the locations north (south) of the X-line, was consistent with an X-line, was consistent with an X-line through the sub-solar X-line through the sub-solar point”point” (Paschmann , 2008) (Paschmann , 2008) .

◆◆ Statistical studies Statistical studies with various IMF clock angleswith various IMF clock angles

Most ⊥to jetsPossible X-line

Paschmann (2002)

Picture fromcomponent MR hypothesis

Pu et al.(2007)A statistical study of 176 jet events from TC-1 observations for dawnward IMF

Most ⊥to jets

A statistical result from TC-1 observations for duskward IMF (Zhang, 2007)

♦(6.1,-3.3,5.5) RE6

(3.5,-7.3,-4.6) RE6

● Y

Cluster

TC-1

Z

(Dunlop et al., 2005)(Dunlop et al., 2005)

●● Global view of Global view of formation formation and motion of FTEs and motion of FTEs

(06 April 2004)(06 April 2004)

DSP (-/+) Cluster (+/-)FTEs ObservationsFTEs Observations

BN bipolar: Cluster (+/-), TC-1 (-/+)

IMF

X-line

FTEs are formed via FTEs are formed via component MRcomponent MR at the low-at the low-latitude dayside MP latitude dayside MP in pairsin pairs, , and moved from the and moved from the source region poleward and dawnward/duskward.source region poleward and dawnward/duskward.

Colling

dH-T dH-T

(Colling et al. 2000)

Global view of FTEs motion and geometryGlobal view of FTEs motion and geometry (Xiao et al. 2005; Pu et al., 2005b; Wang et al2006)(Xiao et al. 2005; Pu et al., 2005b; Wang et al2006) 。。

◆Cluster★ TC1

Highlights of Cluster-Double Star coordinated Highlights of Cluster-Double Star coordinated observation observation (Escoubet et a., 2005)(Escoubet et a., 2005)

● Simultaneous Occurrence of Simultaneous Occurrence of Anti-Anti-Parallel and Component MR under Parallel and Component MR under Similar IMF Conditions (IMF BSimilar IMF Conditions (IMF Byy 0) 0)

◆◆ Component MR: Originated at the low latitudes Component MR: Originated at the low latitudes near the sub-solar point; the MR structures can also near the sub-solar point; the MR structures can also be seen in high-latitudes be seen in high-latitudes

◆◆Anti-parallel MR: Operating in high-latitudes Anti-parallel MR: Operating in high-latitudes and dawn/dusk flanksand dawn/dusk flanks Signatures:Signatures: Null points; jets parallel and anti-parallel Null points; jets parallel and anti-parallel to B fields in the magnetosheath and magnetosphereto B fields in the magnetosheath and magnetosphere, , respectively respectively

Event Overview IMF duskward

Cluster

TC-1 FTE: component MR Cluster MR: anti-parallel

09:4110:37

BL

BM

BN

BN

BL BM

IMF Clock angle

TC-1

◆◆Simultaneous Occurrence of anti-parallel Simultaneous Occurrence of anti-parallel and component MR on 25 Feb, 2005and component MR on 25 Feb, 2005

(Dunlop et al., 2009)

Anti-parallel MR at high-latitudeAnti-parallel MR at high-latitude

Cluster 3 (6.4,2.6,6.8) RE, GSM

BL BM

BN

VL VM

VN

N

T

Null

A

B

Null point reconstruction at high latitude MP (Dunlop et al., 2009)

Feb 25, 2005

5:205:004:00 4:20 4:40DS FTEs Cluster anti-

parallel MR

Cluster

Reversal of jet flow, parallel/anti-parallel to the B in the MSH/MSP

Reversal of VL

Anti-parallel MR at high-latitudeAnti-parallel MR at high-latitude

Component MR

BL

BM

BN

Event Overview IMF dawnward

◆◆Simultaneous Occurrence of anti-parallel Simultaneous Occurrence of anti-parallel and component MR on 06 April, 2004and component MR on 06 April, 2004

Reversal of BN

BNBM

BL

VN VL

VM

Fast flow

N

T

Mixing of MSH & MSP plasmas

(Wang et al.,2008)

A

aa

X line

★Cluster

BN

◆ ◆ 180 (±22.5) 180 (±22.5) IMF (147 events IMF (147 events) )

▲ Fast jet flows are observed at almost all locations on the MPFast jet flows are observed at almost all locations on the MP▲ Most of the jet flows are basically in Z-direction.Most of the jet flows are basically in Z-direction.▲ X-line is basically lying in the Y-direction. X-line is basically lying in the Y-direction.

Z(RE) Z(RE)

Y(RE) Y(RE)

20

-20

10

10

-10-10

-20

00 X-line

●● Global Extent & Global Extent & ConfigurationConfiguration of the X-Line at the MPof the X-Line at the MP

◆◆ Dawnward IMF Dawnward IMF (468 events)(468 events)

▲ S-shape X-line; S-shape X-line; Similar to the previous results ( Pu et al., 2007) ▲ More extended

Z(RE) Z

Y(RE)Y

20

-20

10

-10

0X-line

20100-20 -10

◆ ◆ Duskward IMF Duskward IMF (244 events) (244 events)

▲ Well reconstructed S-shaped X line

Z(RE)Z

Y(RE) Y

20

-20

10

-10

0

20100-20 -10

X-line

◆◆ 135° IMF (158 events)135° IMF (158 events)

▲ X-line elongated to the flank regionsX-line elongated to the flank regions▲ Potential anti-parallel MR outflow in the flankPotential anti-parallel MR outflow in the flank

Z(RE)

Y(RE)

20

-20

10

-10

0

20100-20 -10

Z

Y

X-line

◆◆ -135° IMF (343 events)-135° IMF (343 events)

Z(RE)

Y(RE)

20

-20

10

-10

0

20100-20 -10

Z

Y

X-line

▲ X-line elongated to the flank regionsX-line elongated to the flank regions▲ Potential anti-parallel MR outflow in the flankPotential anti-parallel MR outflow in the flank

● ● Dependence of X-line orientation Dependence of X-line orientation on the IMF Clock Angleon the IMF Clock Angle

θ = 0.24 ( A_IMF – 180o ) + 91o Component MR at Low-latitudes

Rotation of X-Line orientations with different IMF clock angle: Titled angle of X-lines

IMF clock angle

(Zhang, 2007)

III. SummaryIII. Summary(1) CComponent MR dominants at the low-omponent MR dominants at the low-latitude MP latitude MP when IMF Bwhen IMF Byy0 and occurs (there) 0 and occurs (there) for both IMF Bfor both IMF Bzz< 0< 0 and Band Bzz > 0; while in high- > 0; while in high-latitudes, both anti-parallel and component MR latitudes, both anti-parallel and component MR were observed.were observed. “There is no requirement that the shear angle between the magnetic fields on the two sides of the current layer must be 180; it can be 90 or even considerably less. This is particularly relevant for the MP magnetopause, where there are always locations at which the fields are anti-parallel, regardless of the IMF direction, but nature does not appear to prefer those locations”. [From Paschmann (2008)]

(2) (2) FTEsFTEs are formed are formed via component via component MRMR at the low-latitude dayside MP at the low-latitude dayside MP in in pairs, pairs, and moved from the source and moved from the source region poleward and dawnward/ region poleward and dawnward/ duskward.duskward.

◆Cluster

★TC1

(3) (3) Simultaneous occurrence ofSimultaneous occurrence of component and component and anti-parallel MR anti-parallel MR at the low- and high-latitude at the low- and high-latitude MP/ flanks respectively indicates that a large area MP/ flanks respectively indicates that a large area of MP is open for IMF Bof MP is open for IMF Bzz< 0. The < 0. The MR region MR region extens across most of the dayside MP, extens across most of the dayside MP, from from low-latitudes near the subsolar point, to dayside low-latitudes near the subsolar point, to dayside high-latitudes and the dwanside/duskside flank.high-latitudes and the dwanside/duskside flank.

Moore & Fox (2002)Moore & Fox (2002)

Pu et al. (2007)

Duskward IMF

Dawnward IMF

(4) DS & Cluster coordinated measurements DS & Cluster coordinated measurements support the support the 3D3D S Separator MR Model eparator MR Model that a large-that a large-scale X-line joins nulls in opposite polar regions scale X-line joins nulls in opposite polar regions and extends across the dayside MP. The dayside and extends across the dayside MP. The dayside separator line displays properties of both anti-separator line displays properties of both anti-parallel and component MR, with ‘anti-parallel’ parallel and component MR, with ‘anti-parallel’ and ‘component’ being the local features of MR and ‘component’ being the local features of MR near nulls and separator, respectively. near nulls and separator, respectively.

X-lineA Null

●

●

B Null

Law and Finn Law and Finn (1990) (1990)

Wang (1996)Wang (1996)

Dorelli et al. (2007)

X-line

X-line ~Separator

Thanks! Supported by the NSFC Key Programs (No. Supported by the NSFC Key Programs (No. 4073105640731056 ) )

and China Key Research Project (No. G200000784). and China Key Research Project (No. G200000784). The authors thank PIs of Cluster and Double Star Missions The authors thank PIs of Cluster and Double Star Missions

for supporting the data.for supporting the data.

Conjunctions between Cluster Conjunctions between Cluster and Double Starand Double Star

From Jan. to Apr. 2004, From Jan. to Apr. 2004, 2121 MP MP crossings crossings within 1 h within 1 h and and 44 within 15 min.within 15 min.

Cluster

TC1