Flux ropes in space plasmas Alexey Isavnin Department of Physics University of Helsinki, Finland Lectio praecursoria, 14 August 2014
Aug 16, 2015
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
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Space weather
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Space weather describes the conditions in space that affect Earth and its technological systems
Space weather. Spectacular…
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Space weather. Spectacular…
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Space weather. Spectacular but hazardous
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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
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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.
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Tracking a flux rope requires several tools
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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
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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!