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Graduate seminar (2014)
1. Flux ropes in space plasmas
Alexey Isavnin
Supervisors: Emilia Kilpua, Hannu Koskinen
University of Helsinki, Finland
Graduate seminar series 2014, March 24
2.
3. Outline
• Space weather: Sun–Earth connection, its mechanism and
effect on us
• Coronal mass ejections: multipart configuration and
embedded flux ropes
• Evolution of solar flux ropes: deflections and rotations
• Magnetospheric flux ropes: evolution and substorm dynamics
1/31
8. Space weather. How does it work
6/31
Coronal mass ejections (CMEs) are the drivers of the strongest magnetospheric storms.
Geoffective CME is the one that caused geomagnetic disturbance.
11. Magnetic flux ropes
8/31
• Local cylindrical geometry
• Helical magnetic field lines with zero twist in the core and
increasing with the distance from the axis
• Maximum magnetic field strength along the axis
14. CME observations
11/31
CME can be observed in white-light or EUV from several viewpoints and in
situ by a spacecraft it encountered. A flux rope measured insitu is known as
magnetic cloud (MC).
15. Five-part CME structure
12/31
The dark cavity represents the flux rope. Bright core is the prominence
material. Faint loop is the signature of a shock wave driven by the CME.
17. Five-part ICME structure
14/31
Front, rear and MC regions consist from physically different plasma, i.e.
originate from different physical processes or regions near the Sun.
18. Conclusions
15/31
• CMEs and ICMEs are both multipart structures with five
distinct parts distinguishable.
• Flux rope occupies the dark cavity area of a CME observable in
white light.
• Front and rear MC parts originate near the Sun and correspond
to piled-up material (bright loop) in front of the flux rope and
prominence material (bright core), respectively.
• Sheath region region form during fast CME propagation and
occupies the region of diffusive emission.
20. Flux rope evolution
• Expansion
• Longitudinal deflection
• Latitudinal deflection
• Rotation
• Distortion
Motivation: Change of flux rope orientation can result in change of
geomagnetic effectiveness. Important for space weather
forecasting.
16/31
21. Tracking a flux rope requires several tools
17/31
0 Rs 5 Rs 20 Rs 1 AU
solardiskobservations coronagraphimaging in-situmeasurements
22. 18/31
Eruptiveprominence
0 Rs 5 Rs 20 Rs 1 AU
Post-eruption arcades or eruptive prominences give idea about
geometrical orientation of the flux rope in the lower corona.
Flux rope signatures in the lower corona
23. 19/31
0 Rs 5 Rs 20 Rs 1 AU
Coronagraph observations of flux ropes
Forward modeling of ejected flux ropes gives an estimate of their
orientation in the inner heliosphere.
24. 20/31
0 Rs 5 Rs 20 Rs 1 AU
In-situ measurements as a constraint
Local orientation of the flux rope invariant axis is only a constraint for its
global orientation.
MagneticfieldmapbyGrad-Shafranov
reconstruction
25. 21/31
0 Rs 5 Rs 20 Rs 1 AU
Flux rope propagation through MHD solar wind
We propagate the flux rope in 3D through MHD-simulated solar wind
using in-situ measurements as a constraint.
27. Deflection towards equatorial plane
23/31
FluxropeglobalaxisdirectionduringitstravelfromtheSunto1AU.
0 Rs
5 Rs
20 Rs
1 AU
28. Rotation relative to heliospheric current sheet
24/31
Fluxropeorientationsuperimposedonvelocity(top)andmagneticenergydensity
(bottom)mapsat1AUfortwoevents.
29. Conclusions
25/31
• Flux ropes continuously deflect towards the solar equatorial
plane during their travel from the Sun to 1 AU.
• Flux ropes rotate while getting approximately aligned with
heliospheric current sheet.
• Geometrical evolution of ejected flux ropes in the inner
heliosphere was found to be caused by magnetic interaction
with Parker-spiral-structured solar wind.
• 60% of flux evolution happens during the first 14% of their
travel distance from the Sun to 1 AU.
31. Magnetospheric substorm dynamics
26/31
1. Energy from the solar wind due to interaction with magnetic
structures within is stored as excess magnetic flux in the
magnetosphere.
2. A reconnection site (X-line) is formed in the magnetotail.
3. During the explosive substorm reconnection part of excess
energy is released tailwards and part is dissipated in the
ionosphere increasing auroral luminosity.
32. Plasmoid formation
27/31
Plasmoid is a flux-rope-like structure formed between N2 and N3 X-lines. It
carries away the excess energy from the magnetosphere.
33. Multiple X-line reconnection
28/31
Due to plasma instabilities multiple X-lines can be dynamically generated
at the near-Earth reconnection site. Flux ropes formed in between the X-
lines can be released both tailwards and Earthwards.
34. Sequential tailward flux ropes
29/31
An example of a chain of six flux ropes released sequentially tailwards
during just 45 minutes.The sixth flux rope had a larger tilt, speed, core field
and size, and corresponded to the change of solar wind conditions and
formation of new reconnection site.
35. Earthward moving flux ropes
30/31
Earthward moving flux ropes are often registered in far tail and very rarely
in the near tail.The reason is continuous deterioration due to anti-
reconnection process.
36. Conclusions
31/31
• Multi-X-line sites are dynamic regions and result from plasma
instabilities. Flux ropes can be formed and ejected sequentially
from these areas both tailwards and Earthwards.
• The properties of released flux ropes reflect solar wind
conditions and their change correspond to reconfiguration of
the magnetosphere.
• Earthward moving flux rope get deteriorated due to anti-
reconnection and eventually degrade into dipolarization
fronts.
