E. Robbrecht – SIDC- Royal Observatory of Belgium 8 March 2007 The statistical importance of narrow CMEs Open questions to be addressed by SECCHI Eva Robbrecht,

E. Robbrecht – SIDC- Royal Observatory of Belgium 8 March 2007

The statistical importance of

narrow CMEs

Open questions to be addressed by SECCHI

Eva Robbrecht,David Berghmans, Ronald Van der Linden

SIDC – Royal Observatory of Belgium

Look! Our

capricious

sun!

E. Robbrecht – SIDC- Royal Observatory of Belgium 8 March 2007

What are Coronal mass ejections? Plasma clouds leaving the Sun Observationally defined as a new,

discrete, bright feature moving radially outward in the coronagraphic field of view (Hundhausen 1984, Munro 1979, Schwenn 1985)

Many other bright features observed in white light: waves and shocks

Observational characterisation of CME:

Principal angle Angular width Speed: 100 2000 km/s Mass estimate: 1015 g

Severe projection effects Thomson scattering Parameter measurements Halo CMEs

Empirical cone model

angle

width

Halo CME

E. Robbrecht – SIDC- Royal Observatory of Belgium 8 March 2007

CACTus = software for CME detection

top: Polar transformed C2 imageBottom: CACTus CME detection in green

θ

r

E. Robbrecht – SIDC- Royal Observatory of Belgium 8 March 2007

The CACtus software

t

r

Automated detection of CMEs in time-sequences

Aim of software:

Detect appearance of CME + measure important parameterswidth, angle, speedNEW: Propagation direction!

Application:

- Real-time space weather- Post processing catalog of all events- www.sidc.be/cactus- Available via SolarSoft

Data:

- LASCO C2/C3: Qkl and LZ- COR2 total B: beacon and LZ

(A & B)

Requirements: cadence!

CME speed transit time min. cadence- 500 km/s 4hrs in fov COR2 2 images/hr- 1000 km/s 2hrs in fov COR2 4 images/hr - 2000 km/s 1hr in fov COR2 8 images/hr

E. Robbrecht – SIDC- Royal Observatory of Belgium 8 March 2007

Validation of the method

Very good agreement Sigma ~ 10°

Good agreement for θ < 120 ° Large sigma definition? Halo CMEs

CACTus CACTus

CD

AW

CD

AW

Principal angle Angular width

E. Robbrecht – SIDC- Royal Observatory of Belgium 8 March 2007

Statistical analysis of CMEs during solar cycle 23

CACTus CME catalog: 1997 – June 2006 Data: LASCO C2/C3 CACTus application to whole dataset

CME rate over solar cycle Statistics of CME parameters

E. Robbrecht – SIDC- Royal Observatory of Belgium 8 March 2007

1. CME rate during cycle 23

Conclusions [1]

•Solar Cycle well retrieved!•Nmax=3*Nmin

•Delay of 6-12 monthsWhy?Why?

Observed in several activity indicators

1-4 mth: chromospheric and coronal emission lines

10-15 mth: flare rates

Monthly and monthly smoothed rates

E. Robbrecht – SIDC- Royal Observatory of Belgium 8 March 2007

1. CME rate during cycle 23

Conclusions [2]

•Large discrepancy CACTus - CDAW!

•NCDAW = ½ NCACTus

•Nnarrow = ½ NCACTus

Monthly and monthly smoothed rates

E. Robbrecht – SIDC- Royal Observatory of Belgium 8 March 2007

Statistical analysis of CMEs during solar cycle 23

CACTus CME catalog: 1997 – June 2006CACTus CME catalog: 1997 – June 2006 Data: LASCO C2/C3Data: LASCO C2/C3 CACTus application to whole datasetCACTus application to whole dataset

CME rate over solar cycleCME rate over solar cycle Statistics of CME parameters

E. Robbrecht – SIDC- Royal Observatory of Belgium 8 March 2007

CME width distribution

E. Robbrecht – SIDC- Royal Observatory of Belgium 8 March 2007

CME width

CDAW: lognormal distribution log(θ) ~ N(μ,σ) with μ ≈ 30° CACTus: Power-law distribution 5/3

CME has no typical size! CME process is scale invariant!

Well-known result for other types of magnetic field restructuring: E.g. Flare energy distribution (Crosby et al., 1993)

Occurs frequently in nature: earthquakes, avalanche of snow, epidemic disease, stock market

Why are small events systematically excluded by human? instrumental effect, morphology, `detection saturation’ during solar max?

= 1 order of magnitude10 100

Movie

What are they?

Where are they formed? What is the driver?

Is CME process scale invariant?

E. Robbrecht – SIDC- Royal Observatory of Belgium 8 March 2007

CME latitude distribution

E. Robbrecht – SIDC- Royal Observatory of Belgium 8 March 2007

Latitude difference distribution

E. Robbrecht – SIDC- Royal Observatory of Belgium 8 March 2007

Latitude difference distribution

0

30

6090

-30

-60-90

60

30

-30

0

-60

E. Robbrecht – SIDC- Royal Observatory of Belgium 8 March 2007

Narrow events: Discussion

Are they physically different from “classical CMEs”? Does there exist a smallest CME? i.e. cutoff value Narrow events occur frequently at “quiet sun” latitudes

= Position of (mid-latitude) coronal hole boundaries Number and position vary according to solar cycle Are they the “liliputters” of the global magnetic field

restructuring? i.e. are they gradually untying the magnetic field?

Can they trigger “avalanche” CMEs?

E. Robbrecht – SIDC- Royal Observatory of Belgium 8 March 2007

Conclusions

CME rate follows solar cycle is delayed to w.r.t. sunspot rate: 6-12 months

We find much more outflow due to better instruments and new techniques Discussion on CME concept (cfr. Pluto is not a Planet anymore)

Statistics of CME parameters obtained by CACTus differ significantly from classical CME statistics

Statistical importance of narrow events (< 40°) Neglected by observer Obey the observable CME definition

Power law in CME width parameter power ~ - 1.6 suggests that CME process is scale invariant occur at mid-latitudes and active region latitude