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