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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
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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.
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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.
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Swedish National Graduate School of Space Technology
The magnetosphere and Cluster spacecraft orbit
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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
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Results from 3D analysis
To be coupled with data from the Cluster spacecraft*
*Grammatical notation: One spacecraft, several spacecraft
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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)
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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
)
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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
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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.
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