Near-Earth Magnetotail Reconnection and Plasmoid Formation in Connection With a Substorm Onset on 27...

Near-Earth Magnetotail Reconnection Near-Earth Magnetotail Reconnection and Plasmoid Formation in Connection and Plasmoid Formation in Connection With a Substorm Onset on 27 August With a Substorm Onset on 27 August

20012001

S. ErikssonS. Eriksson11, M. Oieroset, M. Oieroset22, D. N. Baker, D. N. Baker11, C. , C. MouikisMouikis33,,

M. W. DunlopM. W. Dunlop4, H. Reme, H. Reme5, R. E. Ergun, R. E. Ergun11, and A. , and A. BaloghBalogh6

11 Laboratory for Atmospheric and Space Physics, University of Colorado at Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder, USABoulder, USA22 Space Sciences Laboratory, University of California at Berkeley, USA Space Sciences Laboratory, University of California at Berkeley, USA33 Space Science Center, University of New Hampshire, USA Space Science Center, University of New Hampshire, USA4 Rutherford Appleton Laboratory, UK Rutherford Appleton Laboratory, UK5 Centre d’Etude Spatiale des Rayonnements, France Centre d’Etude Spatiale des Rayonnements, France6 Imperial College, UK Imperial College, UK

Contact information:

[email protected]

OutlineOutline

IntroductionIntroduction1.1. Tail reconnection and slow-mode shocksTail reconnection and slow-mode shocks2.2. deHoffmann-Teller and Walen analysesdeHoffmann-Teller and Walen analyses

Cluster observations and Walen Cluster observations and Walen analysesanalysesAugust 27 2001 from 03:50 UT to 04:35 UT (post-midnight event)

SummarySummary

Tail Reconnection and Slow-mode Tail Reconnection and Slow-mode ShocksShocks

[Hill, T.W., JGR, 80, 4689, 1975][Feldman et al., JGR, 92, 83, 1987]

• Acceleration in tail reconnection is assumed to take place across a slow-mode shock connected to the diffusion region. Configuration essentially that of Petschek [1964] (above right).



• Slow-mode shocks are defined in ideal MHD by an increased plasma pressure and a decreased B-field strength where the B-field bends toward the shock normal.



• Slow-mode shocks were first observed in the tail by e.g. Feldman et al. [1984, 1987] using the Rankine-Hugoniot jump conditions. Also suggested by Oieroset et al. [2000] who successfully used the Walen analysis on Wind data 60 Re downtail.

M

m

mm BvvM

vD

D(v)V

BvE

V

v,v

BB

n

1

2)()(

HT

HT

(2)(1)

)2()1(

1)(

: minimizingby obtained

0ely validapproximat

is MHDideal that Assuming

velocityframeTeller deHoffmann:

velocitymeasured :

field magnetic measured:,

normalshock :ˆ

deHoffmann-Teller AnalysisdeHoffmann-Teller Analysis

[Khrabrov and Sonnerup, ISSI Sci.rep., 1998]

• The existence of an HT frame indicates the presence of a quasi-stationary coherent pattern of magnetic field and plasma velocity. The HT interval should include data points on either side of the boundary.

M

m

mm BvvM

vD

D(v)V

BvE

V

v,v

BB

n

1

2)()(

HT

HT

(2)(1)

)2()1(

1)(

: minimizingby obtained

0ely validapproximat

is MHDideal that Assuming

velocityframeTeller deHoffmann:

velocitymeasured :

field magnetic measured:,

normalshock :ˆ

deHoffmann-Teller AnalysisdeHoffmann-Teller Analysis

[Khrabrov and Sonnerup, ISSI Sci.rep., 1998]

• A Galilean HT frame transformation allows for the identification and analysis of such coherent structures (e.g. slow-mode shocks) moving past an observing platform.

Walen Analysis as a Test of Walen Analysis as a Test of ReconnectionReconnection

(Not a slow shock since B does not bend toward normal)• Reconnection predicts that

the generated “rotational discontinuity” (finite normal B-field component) propagates away from the diffusion region at a field-aligned phase speed in the HT shock frame and its magnitude is determined by the type and strength of the shock.

1A*A2A

0

*A

A

HT

shock) mode(slow '

use)(magnetopa '

'

'

MMM

BMv

vv

BB

vvv

Walen Analysis as a Test of Walen Analysis as a Test of ReconnectionReconnection

(Not a slow shock since B does not bend toward normal)• The sign of the Walen

slope depends on whether the B-field is parallel or antiparallel to the flow direction.

1A*A2A

0

*A

A

HT

shock) mode(slow '

use)(magnetopa '

'

'

MMM

BMv

vv

BB

vvv

Walen Analysis in the MagnetotailWalen Analysis in the Magnetotail

Walen slope

Oieroset et al., JGR, 105, 25,247, 2000.

• Region I: earthward jet, Bx>0, RW<0• Region II: tailward jet, Bx>0, RW>0

Walen Analyses at Wind (x= -60 Walen Analyses at Wind (x= -60 Re)Re)

Oieroset et al., JGR, 105, 25,247, 2000.

Note that there is no ion composition in the Wind data set and that these slopes were derived assuming 100% H+.

• Earthward jet interval

• Negative Bx

• Walen slope should be positive

Cluster Location August 27 2001Cluster Location August 27 2001

Cluster Observations on August 27 Cluster Observations on August 27 20012001

Density (CODIF)

Plasma (CODIF)

Ion speed (HIA)

[Vx, Vy, Vz]

Alfven Mach numberNote: MA<1

Magnetic field magnitude

A B C

[Bx, By, Bz]

Cluster Observations on August 27 Cluster Observations on August 27 20012001

Density (CODIF)

Plasma (CODIF)

Ion speed (HIA)

[Vx, Vy, Vz]

Alfven Mach numberNote: MA<1

Magnetic field magnitude

[Bx, By, Bz]

Approximate substorm onset in global UV images at ~04:06-04:08 UT [Baker et al., GRL, 2002]

A B C

Comparison with the Substorm of April Comparison with the Substorm of April 24 197924 1979

Overview of ISEE 2 magnetic field (GSE) and plasma data near substorm onset.

[Hones et al.,1986; Feldman et al., 1987]

Bx

By

Bz

beta

Vx

sc1sc3

Bx

By

Vx

Pp

Bz

Comparison with the Plasmoid of April Comparison with the Plasmoid of April 24 197924 1979

Three-dimensional magnetic field structure of plasmoid at substorm onset [from Hones et al., GRL, 1982].

Cluster magnetic fieldhodogram (GSM)

Walen Analyses on August 27 2001Walen Analyses on August 27 2001(A) (A) Tailward Region II Jets 04:00-04:03 UTTailward Region II Jets 04:00-04:03 UT

sc1

sc3

•Positive Bx•Tailward jets•Prediction: Positive Region II Walen slope

Walen Analyses on August 27 2001Walen Analyses on August 27 2001(B) (B) Earthward Region I Jets 04:06-04:10 UTEarthward Region I Jets 04:06-04:10 UT

sc1 04:06-04:08 UT

•Positive Bx•Earthward jets•Prediction: Negative Region I Walen slope

sc3 04:09-04:10 UT

Walen Analyses on August 27 2001Walen Analyses on August 27 2001(C) (C) Earthward Region I Jets 04:26-04:28 UTEarthward Region I Jets 04:26-04:28 UT

sc1

sc3

•Positive Bx•Earthward jets•Prediction: Negative Region I Walen slope

bbvv

B

Bbbvbv

ˆˆ

ˆ whereˆˆ

||

x: blacky: greenz: red

Angle between V and B ….

BA C

Substorm of 27 August Substorm of 27 August 20012001

(A)


(B)


(B)

(C)

Note on Importance of Density Note on Importance of Density for the Walen Slopefor the Walen Slope

itot

ieff

efftot

mnnm

mn

BMvv

0AHT

A mix of 5% O+ ions and 95% H+ results in an effective mass m=1.75mp and a lower Alfven speed, that effectively should increase the Walen slope ….

Impact of m=mp AssumptionImpact of m=mp Assumption

O+ fraction: 0.8% - 4.8%Avg O+ fraction: 1.8%Walen slope=0.73

Assume 100% H+Walen slope=0.65

SummarySummary The Walen test together with the location of The Walen test together with the location of

Cluster north of the neutral sheet confirms Cluster north of the neutral sheet confirms the presence of a slow mode shock on the the presence of a slow mode shock on the tailward side of the near-Earth X-line on tailward side of the near-Earth X-line on August 27, 2001 that most likely accelerated August 27, 2001 that most likely accelerated the ions.the ions.

The Walen test for some earthward jets may The Walen test for some earthward jets may indicate a correct slope (sign), although the indicate a correct slope (sign), although the quality of the HT frame is lower.quality of the HT frame is lower.

The earthward jets seem to be more field-The earthward jets seem to be more field-aligned which implies that ideal MHD (and aligned which implies that ideal MHD (and thus the HT analysis) breaks down.thus the HT analysis) breaks down.

The use of ion composition data from CODIF The use of ion composition data from CODIF improved the Walen slope.improved the Walen slope.

Near-Earth Magnetotail Reconnection and Plasmoid Formation in Connection With a Substorm Onset on 27...

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