Solar-C and the Sun-Earth Connection
Len Culhane
Mullard Space Science Laboratory
University College London

Some Key Areas for the Sun-Earth Connection• Solar activity, leading to CMEs and flares, and the solar wind are the keys to
the Sun-Earth connection – a subset of the Sun’s role in the Heliosphere• Magnetic flux generated at the bottom of the convection zone emerges throughthe photosphere. Need to:– clarify nature of emerged magnetic structures and flux rope formation– identify sub-photospheric magnetic structures• CME launch process and related magnetic configurations must be understood– on-disc and coronal signatures (filaments, dimming, EIT waves, sigmoids) are important• CMEs remove magnetic helicity from the Sun– a tool for eruption forecasting?

• Interplanetary CMEs (ICMEs) and Magnetic Clouds (MCs) interact with nearEarth environment– clarify their magnetic and compositional relationship to the original CME•

We will briefly outline the above topics in relation to the Solar-C plans
Wednesday 19th November, 2008

Solar-C Science Definition Meeting – ISAS/JAXA2

Flux Emergence at Photosphere•••B - photosphereVelocity - Hα+ ve polarity motion

G Band - photosphereLine Centre - Hα- ve polarity motion

Strauss and Zwann, 1999
courtesy of Lidia van Driel’s UCL
undergraduate lectures!

Emergence of a bipolar plage region- sequence of polarity emergence- Hα filament system: vup < 10 km s-1; vdown< 50 km s-1; 20 min lifetime- opposite polarities move apart: v < 2 km s-1 first half hour; v ~ 1.3-0.7 km s-1 next six hours
Scenario consistent with the emergence of a fragmented Ω-shaped loop
- still connected to the toroidal flux in the dynamo (tachocline) region
See recent Hinode result by Okamoto et al. 2008
Wednesday 19th November, 2008

Solar-C Science Definition Meeting – ISAS/JAXA

Hinode Observation of an Emerging Flux-rope• Okamoto et al., 2008 used a time series of vector fields below a prominence• Horizontal field along polarity
inversion line (PIL) changeddirection• Horizontal field region
was blueshifted• Upper panels show angle
between PIL andhorizontal field- θ positive: normal- θ negative: inverse• Lower panels show schematicof emerging flux-rope

Apr 29 11:40

Apr 30 05:03

Apr 29 15:33

Apr 29 20:14

Apr 30 15:44

May 01 02:02• These are clearly subtle anddifficult observations but
definitive results are needed
4Wednesday 19th November, 2008

Solar-C Science Definition Meeting – ISAS/JAXA

Flux Emergence Below the Surface (Kosovichev, 2007)• Subsurface region of
anomalous flow velocity
suggests emerging
Ω loop• Need to identify fluxrope structures to as
great a depth as possible- ideally to tachocline• Deploy optimum
Helioseismology approach• Compelling results need to be achieved for the solar activity latitude range

Wednesday 19th November, 2008

Solar-C Science Definition Meeting – ISAS/JAXA

CME Launching - Dimming Event of 12-May-1997• Features include:- twin dimming regions- simple magnetic structure- LDE flare GOES class C 1.3- brightening along and shrinkage of northpolar coronal hole boundary- fiament eruption- coronal wave
- full Halo CME- associated magnetic cloud at Earth• Well-studied event (Thompson et al., 1998, Webb et al., 2000, Zhukov and Auchére, 2004,Attrill et al., 2006)
6Wednesday 19th November, 2008

Solar-C Science Definition Meeting – ISAS/JAXA

CME Models• Single class of models
discussed here
- ideal MHD instabilities• Many other energy storage
and release models exist• Kink Instability- occurs when twist in flux rope exceeds a

critical value of 2.5 π (Priest & Hood, 1979)- driven by conversion of twist into writhe- example observed by TRACE in 2004,Nov 10Fan (2005)

Williams et al., (2005)• Torus instability- occurs if the overlying field drops

sufficiently fast with height.
- driven by hoop force of a flux rope
(Lorentz force of a current ring)•

Kink instability may precede Torus eruption
Wednesday 19th November, 2008

Solar-C Science Definition Meeting – ISAS/JAXA

Török & Kliem, (2007) 7

CME Models•

All the models require understanding the competition between magnetic
pressure forces ( expansion) and magnetic tension forces (restraining)•Difficult to tell which model is correct- combination of different models involved?
Expected observational differences between the models are subtle•• Hard to distinguish between e.g. a pre-eruption flux rope ( flux cancellation; Linker et al.,2003 ) and a collection of strongly sheared field lines ( breakout; Antiochos et al., 1999)• After eruption both models have a flux rope
• Flux ropes may also emerge from below the photosphere•

Models are not yet able to predict observable quantities•

Require study of CME acceleration sites, pre-CME structures, pre flare indicators- clarify energy buildup- understand energy release mechanism
8Wednesday 19th November, 2008

Solar-C Science Definition Meeting – ISAS/JAXA

Role of Magnetic Helicity•

Magnetic Helicity, H is a globally conserved quantity that can describe the stress present in
a complex magnetic configuration•Helicity is removed from the corona to the Interplanetary Medium (IPM) by CMEs
– total helicity content of an Active Region may indicate CME productivity or even show threshold
behaviour•

Determine Hr by e.g. linear force-free extrapolation of photospheric field to the corona
where α is determined from a best fit to coronal loops• Hr is then determined from the relation

with summation over the spatial Fourier modes of the extrapolated field
9Wednesday 19th November, 2008

Solar-C Science Definition Meeting – ISAS/JAXA

Compare ΔHcorona with HMagnetic Cloud
AR 7912, 14 Oct. 1995

2-3 days later

beforeCME

afterCMEMC• Remote sensing but global observation- magnetograms + coronal loops + extrapolation-> Δ Ηcorona• Results so far are suggestive but qualitative• In situ but local observation

time (h)- measure three B components + flux rope model-> HMC• For future, use non-linear force-free extrapolation with vector B-field measurements
Wednesday 19th November, 2008

Solar-C Science Definition Meeting – ISAS/JAXA

In-Situ Observations of ICMEs• CMEs are called ICMEs in Interplanetary space• CMEs are observed in situ as transients in IP

space with changes to ambient physicalparameters:- stronger magnetic field showing a

twisted flux rope structure- higher density and lower temperaturethan the surrounding solar wind.

11
Wednesday 19th November, 2008

Solar-C Science Definition Meeting – ISAS/JAXA

In-Situ Observations of ICMEs• Magnetic Field- Strength increase >10 nT.
(Hirshberg & Colburn, 1969)- Smooth rotation of the magnetic field direction(Klein & Burlaga,1982)- Lack of fluctuations(Pudovkin et al., 1979)- Discontinuities at ICME boundaries(Janoo et al., 1998)• Plasma- ~ 50% of ICMEs are associated with IP shocks- Extreme density decrease ≤ 1cm-3 (Richardson et al., 2000)- Proton temperature decrease (Gosling et al., 1973)- Low plasma β (ratio of gas to magnetic pressure)• Magnetic Cloud (MC)- Specialist title given to an ICME when the core can be unambiguously identified (Klein & Burlaga, 1982)12Wednesday 19th November, 2008

Solar-C Science Definition Meeting – ISAS/JAXA

In-Situ Observations of ICMEs• Composition•

The abundances of elements and their charge states tend to rise within ICMEs- characteristic of having originated in the Sun’s Corona.
→ Enhanced α/proton ratio: He2+/H+ > 8%
→ Over 80% of MCs have elevated O andFe charge states: e.g. O7+/O6+ >1→ Occurrence of He+: He+/He2+ > 0.01
→ Enhancements of Fe/O
→ Unusually high ratios of 3He/4HeFe Charge State Distributions observed with ACE•ACE example for near-Earth MC shows:- highest ion stages at front, lower at rear
- coronal followed by chromospheric material•

However this is a simple example- exact composition can be unique (Gloeckler et al., 2005)
Wednesday 19th November, 2008

Lepri et al., (2001)

Solar-C Science Definition Meeting – ISAS/JAXA

13

Relevance of Solar-C• Subset of Sun-Earth connection topics has been reviewed that includes- Search for evidence of existence of flux tubes – above and below the photosphere- CME Launch processes- Measurement and use of magnetic helicity- In-situ registration of arriving ICMEs/MCs• Emerging flux rope studies require high quality vector magnetograms withgood cadence and a field of view greater than AR size to be available in
the AR latitude range• No clear advantage for Plan A• Formation of flux ropes at the tachocline and their passage through theconvection zone
- high latitude observations may allow flow and anomalous velocity studies to tachocline
14• Posible Plan A advantage; SDO/HMI and Plan B abilities to be quantified
Wednesday 19th November, 2008

Solar-C Science Definition Meeting – ISAS/JAXA

Relevance of Solar-C (continued)• CME launch process needs- understanding of the flux rope formation process- identification of role of pre-launch phenomena- observation of the associated disc and low corona signatures- multiple views of CME expansion→ implies a heliospheric imager or coronagraph for Plan A• Plan A and Plan B both have role
- Plan A allows CME tracking by contributing to multiple views- Plan B allows detailed views of the pre-launch processes

15Wednesday 19th November, 2008

Solar-C Science Definition Meeting – ISAS/JAXA

Relevance of Solar-C (continued)• Quantitative magnetic helicity measurements require high quality vector
magnetic field measurements good cadence and a field of view
significantly greater than AR size to be available in the AR latitude range• Automated NLFF magnetic field extrapolation code also required• Assuming SDO AIA/HMI capability exists, no advantage for Plan A- need better understanding of Plan B capabilities• In-situ sampling of ICMEs/MCs at range of latitudes requires- Sensitive magnetometer measurements- Solar wind and ICME electron/proton plasma analyser- Plasma composition measurements by ion mass spectrometer• Plan A sampling advantage if spacecraft has these instruments
Wednesday 19th November, 2008

Solar-C Science Definition Meeting – ISAS/JAXA

16

Thank You

17
Wednesday 19th November, 2008

Solar-C Science Definition Meeting – ISAS/JAXA