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The statistical importance of narrow CMEs

The statistical importance of narrow CMEs. Look! Our capricious sun!. Open questions to be addressed by SECCHI Eva Robbrecht, David Berghmans, Ronald Van der Linden SIDC – Royal Observatory of Belgium. Empirical cone model. width. angle. What are Coronal mass ejections?.

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The statistical importance of narrow CMEs

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  1. The statistical importance of narrow CMEs Look! Our capricious sun! Open questions to be addressed by SECCHI Eva Robbrecht, David Berghmans, Ronald Van der Linden SIDC – Royal Observatory of Belgium

  2. Empirical cone model width angle 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 Halo CME

  3. CACTus = software for CME detection r θ top: Polar transformed C2 image Bottom: CACTus CME detection in green

  4. r t The CACtus software Automated detection of CMEs in time-sequences • Aim of software: • Detect appearance of CME + measure important parameters • width, angle, speed • NEW: 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

  5. Very good agreement Sigma ~ 10° Good agreement for θ < 120 ° Large sigma  definition? Halo CMEs Validation of the method Principal angle Angular width CDAW CDAW CACTus CACTus

  6. 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

  7. 1. CME rate during cycle 23 • Conclusions [1] • Solar Cycle well retrieved! • Nmax=3*Nmin • Delay of 6-12 months • Why? Observed in several activity indicators 1-4 mth: chromospheric and coronal emission lines 10-15 mth: flare rates Monthly and monthly smoothed rates

  8. 1. CME rate during cycle 23 • Conclusions [2] • Large discrepancy CACTus - CDAW! • NCDAW = ½ NCACTus • Nnarrow = ½ NCACTus Monthly and monthly smoothed rates

  9. 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

  10. CME width distribution

  11. 10 100 = 1 order of magnitude 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? What are they? Where are they formed? What is the driver? Is CME process scale invariant? Movie

  12. CME latitude distribution

  13. Latitude difference distribution

  14. 90 60 60 30 30 0 0 -30 -30 -60 -60 -90 Latitude difference distribution

  15. 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?

  16. 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

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