Swedish National Graduate School of Space Technology

Cluster multi-spacecraft measurements: applications on transition layer development and location of the

reconnection site

Lars-Göran Westerberg1, Hans O. Åkerstedt1 and Hans Nilsson2

1Division of Fluid Mechanics

Luleå University of Technology2Swedish Institute of Space Physics, Kiruna

Swedish National Graduate School of Space Technology

Outline

• Introduction

- Objective of present paper.- The magnetosphere and Cluster spacecraft orbit.- Magnetic reconnection and the Cluster mission.

• Cluster in situ measurements coupled with a 3D analysis.

• Conclusions and future work.

Swedish National Graduate School of Space Technology

Objective of present paper

Combine results from a 3D analysis covering the plasma flow near a reconnection site with in situ Cluster observations, in order to study:

Development of the magnetopause transition layer.

Values on the anomalous transport coefficients (ν + ηd), where ν is the kinematic viscosity and ηd the magnetic diffusivity.

Also estimate the distance from the observing spacecraft to the reconnection site.

Swedish National Graduate School of Space Technology

The magnetosphere and Cluster spacecraft orbit

Swedish National Graduate School of Space Technology

Magnetic reconnection

• Main mechanism for the transfer of mass and momentum in space and astrophysical applications.

• Magnetic field seize to be frozen in the plasma. The resistivity is locally finite.

Credit: European Space Agency

Swedish National Graduate School of Space Technology

Results from 3D analysis

To be coupled with data from the Cluster spacecraft*

*Grammatical notation: One spacecraft, several spacecraft

Swedish National Graduate School of Space Technology

y

z

x

Cluster spacecrafts

Magnetopause

~8 RE

~9 RE

Earth

Bow shock

zx

Magnetosheath

y

Sub-Solar point

a

b

c

sc1

sc4

sc3

-0.5 0 0.5 1-0.1

0

0.1

0.2

0.3

y (RE)

z

(RE)

-0.5 0 0.5 1-0.1

0

0.1

0.2

0.3

x (RE)

z

(RE)

sc1

sc4

sc3

sc1

sc4

sc3

Joint position on the 13th of January 2002

Sub-solar region

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Cluster sc1 data during 14:50-15:50

Time (UT)

Swedish National Graduate School of Space Technology

70

90

110

130

150

170

190

210

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5-30

-25

-20

-15

-10

-5

0

5

10

15

Results from Cluster and theory

x (RE)

B (

nT)

V (

km/s

)

Swedish National Graduate School of Space Technology

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.5

1

1.5

2

2.5

3

3.5

4

(distance to reconnection line)

y

z Z

x

UHT

reconnection line

Z0

satellite

a

Z (Distance from reconnection site)

b

δ(Z)

sc4 sc3 sc1

Location of reconnection line and transition layer development

Solid line: Theoretical expression. Cross marks: Measured thickness by respective spacecraft

Swedish National Graduate School of Space Technology

Conclusions and future work

Maximum value of anomalous transport coefficients ~ 104 km2/s.

Cluster satellites pass the magnetopause ~ 0.5 RE

from the reconnection site.

Magnetopause transition layer increases when moving away from the reconnection site.

Enhance the data analysis – statistical study of magnetopause crossings.

Develop the theory by including Hall terms as non-ideal effects.

Swedish National Graduate School of Space Technology

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