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Flux ropes in space plasmas Alexey Isavnin
Department of Physics University of Helsinki, Finland
Lectio praecursoria, 14 August 2014
“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
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
Space weather
2/18
Space weather describes the conditions in space that affect Earth and its technological systems
Space weather. Spectacular…
3/18
Space weather. Spectacular…
4/18
Space weather. Spectacular but hazardous
5/18
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.
Space weather. How does it work
7/18
1 2
3 4
Flux rope CMEs and their internal structure
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
Coronal mass ejection
9/18
CMEs are not just explosions on the Sun but eruptions of magnetic flux ropes.
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.
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.
Evolution of solar flux ropes
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
Tracking a flux rope requires several tools
13/18
0 Rs 5 Rs 20 Rs 1 AU
solar disk observations coronagraph imaging in-situ measurements
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.
Evolution of magnetospheric flux ropes
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.
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.
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.
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.
Thanks for your attention!