Lectio Praecursoria from PhD defence at University of Helsinki in 2014.

1. Flux ropes in space plasmas
Alexey Isavnin
Department of Physics
University of Helsinki, Finland
Lectio praecursoria, 14 August 2014

2. “If I had to choose a religion, the Sun as the
universal giver of life would be my god.”
Napoleon Bonaparte
“Neither the Sun nor death can be looked at
steadily.”
François La Rochefoucauld

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
1/18

4. Space weather
2/18
Space weather describes the conditions in space that affect Earth
and its technological systems

5. Space weather. Spectacular…
3/18

6. Space weather. Spectacular…
4/18

7. Space weather. Spectacular but hazardous
5/18

8. Space weather. How does it work
6/18
Coronal mass ejections (CMEs) are the drivers of the strongest geomagnetic
storms. Geoffective CME is the one that caused geomagnetic disturbance.

9. Space weather. How does it work
7/18
1 2
3 4

10. Flux rope CMEs and their internal structure

11. Magnetic flux ropes
8/18
• 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

12. Coronal mass ejection
9/18
CMEs are not just explosions on the Sun but eruptions of magnetic flux ropes.

13. Five-part CME structure
10/18
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.

14. Conclusions
11/18
• 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 ICME 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.

15. Evolution of solar flux ropes

16. Solar flux rope evolution
• Expansion
• Deflection
• Rotation
• Distortion
Motivation: Change of flux rope orientation can result in change of
geomagnetic effectiveness. Important for space weather
forecasting.
12/18

17. Tracking a flux rope requires several tools
13/18
0 Rs 5 Rs 20 Rs 1 AU
solardiskobservations coronagraphimaging in-situmeasurements

18. Conclusions
14/18
• Flux ropes continuously deflect towards the solar equatorial
plane during their travel from the Sun to the Earth’s orbit.
• 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 rope evolution happens during the first 14% of
their travel distance from the Sun to 1 AU.

19. Evolution of magnetospheric flux ropes

20. Magnetospheric substorm dynamics
15/18
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.

21. Plasmoid formation
16/18
Plasmoid is a flux-rope-like structure formed between N2 and N3 X-lines. It
carries away the excess energy from the magnetosphere.

22. Multiple X-line reconnection
17/18
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.

23. Conclusions
18/18
• 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.

24. Thanks for your attention!