Plasma properties in eruptive prominences

Nicolas Labrosse

University of Glasgow, Scotland, UK

With help from Scott Forrest

Motivation

Understanding how the prominence plasma evolves during an eruption can shed light on

CME initiation mechanisms

Link between chromosphere and heliosphere

Outline

Effect of plasma motion on emergent radiation

Non-LTE modelling

Results for the He II 304 Å line

Comparison with SDO/AIA observations

Motivation and Outline

11/06/2013 Nicolas Labrosse - IAU Symposium S300, Paris 2

Theoretical calculations have shown that when solar prominences

move away from the surface of the Sun, their radiative output is

affected via the Doppler dimming or brightening effects. Hyder & Lites (1970), Heinzel & Rompolt (1987), Gontikakis et al (1997), Labrosse et al

(2007, 2008)

Doppler dimming (brightening) is the decrease (increase) in intensity

of a line formed by resonant scattering of the incident radiation from

the Sun due to the radial motion of the plasma.

Mostly strong resonance lines are affected by this effect.

Similar effect used to diagnose solar wind speed Kohl & Withbroe (1982)

Effects of plasma motions on EPs radiation

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The prominence model

•1D plane-parallel vertical slab

Free parameters Gas pressure

Temperature

Column mass

Height above the limb

Radial velocity

Equations to solve Pressure equilibrium, ionisation and

statistical equilibria (SE), radiative

transfer (RT) for H (20 levels)

SE, RT for other elements: He I (29

levels) + He II (4 levels)

The prominence model

Multi-level, multi-line

non-LTE modelling

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Doppler dimming/brightening depends on

•Line formation mechanism

•Strength / shape of incident radiation

•Coupling with other energy states

•Coupling with other lines

Effects of plasma motions on EPs radiation

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V=0 km s-1

V=80 km s-1

V=200 km s-1

V=400 km s-1

5 11/06/20

13 T = 8000 K T = 15000 K

Labrosse et al (2010)

6

He II 304 Å line sensitive to Doppler dimming

line mostly formed by scattering of incident radiation coming from the Sun

Plasma motions in prominences

Nicolas Labrosse - IAU Symposium S300, Paris 11/06/2013 Labrosse et al. (2007)

7

Results (5)

Doppler dimming of He resonance lines stronger if:

Cool plasma

Not too dense

Large temperature gradient in PCTR

Increasing column mass with all other parameters kept constant means more hot material → collisional component becomes more important ⇒ the line is less sensitive to Doppler dimming

Doppler dimming of He resonance lines

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Constant plasma parameters

Question

Is Doppler dimming observed in eruptive prominences?

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9

2010-06-13

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SDO/AIA observations

10

2010-06-13

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SDO/AIA observations

2011-06-10

This study shows that...

Variation of He II 304 intensity with radial velocity

Decreases in some cases, increases in others

Comparison with non-LTE computations

Variation of plasma parameters and Doppler dimming effect explain changes in He II 304 intensity

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Labrosse & McGlinchey (2012)

Eruption of 19 March 2011 observed by AIA

Plasma diagnostics

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Eruption of 19 March 2011 observed by AIA

Plasma diagnostics

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Surface pressure

decreases during

eruption as EP rises

Perspectives

Extreme Ultraviolet Imager

on Solar Orbiter

•Combining with in-situ data out of the ecliptic

•Better understanding of physical conditions within EPs

•Better understanding of links between EPs and dynamic heliosphere

•EUI will monitor the low atmosphere

counterparts of large-scale solar eruptive

events such as CMEs.

•It will ideally be suited to study

prominence eruptions.

•Using both H Ly-α and He II 304 lines will

add constraints on the models.

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Conclusions

•EP plasma parameters obtained

•minimizing differences between observables and model parameters

•New non-LTE models

•Explain intensity variations by changes in plasma parameters

•Are able to reproduce qualitatively SDO/AIA observations

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TAKK!

Royal Astronomical Society

Specialist Discussion Meeting

Friday 21st February 2014

London

The Life of Solar Prominences

Organisers:

Nicolas Labrosse

Duncan Mackay

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