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

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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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3 4

Flux rope CMEs and their internal structure

Magnetic flux ropes

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•  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

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CMEs are not just explosions on the Sun but eruptions of magnetic flux ropes.

Five-part CME structure

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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

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•  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

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•  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

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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

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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

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•  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!