FRi3D: a novel 3D model of CMEs

1. FRiƐD: a novel 3D model of CMEs
Alexey Isavnin
University of Helsinki

2. Why model CMEs in 3D?
1. Space weather forecasting in relation to CMEs
includes prediction of both arrival time and magnetic
field.
2. In-situ magnetic field and arrival time depend on
geometry of the encounter with a CME.
3. CMEs experience global 3D deformations that alter
their local properties.

3. ●
Reasonable 3D geometry
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Support for typical deformations
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Expansion
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Deflection
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Rotation
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”Pancaking” due to radial expansion
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Skew due to solar rotation
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Front flattening (fast CMEs)
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3D magnetic field configuration
What a CME model should be capable of?
Common approach: focus on one or two characteristics
of CME structure and evolution and neglect all the others.
Solution: let's merge all the major aspects of CMEs
into a single model: Flux Rope in 3D or FRi3D.

4. Starting with simplified hydrodynamic description:
magnetic slingshot in a radial outflow.
Balance of hydrodynamic forces and magnetic tension
provides an estimate for the shape of a CME.
Figuring out the shape of CME

5. Figuring out the shape of CME
The solution supports front flattening with a single parameter.

6. ”Pancaking” and rotational skew can be easily introduced
via geometric transformations.
”Pancaking” and rotational skew
”pancaking” rotational skew

7. The shell is continuously analytic and supports deformations.
3D shell of the FRi3D model
front flattening ”pancaking” rotational skew

8. Classical Lundquist representation: twist increases towards
the edge of a flux rope going to infinity.
Twist of magnetic field-lines in a flux rope

9. The twist in flux-rope CMEs is low and constant
contradictory to the Lundquist solution
center edge
Hu et al., 2015
Lundquist solution
Twist of magnetic field-lines in a flux rope

10. FRi3D with constant twist and flux conservation

11. Cross-section of the FRi3D model
FRi3D model MHD simulations
FRi3D reproduces pancaking similarly to MHD simulations.

12. Synthetic in-situ measurements of magnetic field
cross through the apex

13. Fitting FRi3D to a real CME: white-light

14. Fitting FRi3D to a real CME: in-situ
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only pancaking expansion
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completely independent
from remote observations
Results
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deflection and rotation
towards equatorial plane
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slight overexpansion

15. Fitting FRi3D to a real CME: in-situ

16. Comparison with Grad-Shafranov reconstruction
GS reconstruction FRi3D model
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unrealistic circular shape
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underestimated impact distance
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realistic pancaked shape
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larger imact distance

17. Outlook
FRi3D can be applied to any white-light and in-situ
observations, which gives numerous possibilities
for future studies:
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non-trivial geometries of spacecraft-CME encounters, e.g.,
through the leg of a CME
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multi-spacecraft and spacecraft line-up events → CME
evolution, space weather forecasting
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3D fits of heliospheric imager data → space weather
forecasting, for L5 missions especially
●
input to MHD simulations → CME evolution, CME-CME
interaction