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“Reconnection along a streamer Current Sheet induced by a CME expansion”

“Reconnection along a streamer Current Sheet induced by a CME expansion” A. Bemporad 1 , G. Poletto 1 , F. Landini 2 , M. Romoli 2 1 INAF – Arcetri Astrophysical Observatory 2 University of Florence, Astronomy Department. UVCS slit. UVCS slit. UVCS slit. The January 10-11, 2005 CME.

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“Reconnection along a streamer Current Sheet induced by a CME expansion”

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  1. “Reconnection along a streamer Current Sheet induced by a CME expansion” A. Bemporad1, G. Poletto1, F. Landini2, M. Romoli2 1INAF – Arcetri Astrophysical Observatory 2University of Florence, Astronomy Department

  2. UVCS slit UVCS slit UVCS slit The January 10-11, 2005 CME (LASCO/C2 difference movie) • Before the event: • Streamer complex in the West limb • The event: • CME first appear.: 10/12, 18:36 UT • Slow CME: v(20 Rʘ)=320 km/s • Accelerating: a ~ 4.5 m/s2 • During/after the event: • Outflows along two lateral streamers (LASCO/C2 images)

  3. Outline • Coronal background magnetic configuration • LASCO data: post-CME evolution of a streamer CS • UVCS data: evolution of CS physical parameters • during reconnection • Conclusions

  4. East limb West limb outflow outflow Outflows along streamers possibily induced by the CME propagation. …through which physical processes? (from http://ccmc.gsfc.nasa.gov/ ) The magnetic configuration CME • On December 10-11 a system of ARs is crossing the West limb (GOES/SXI) • Photospheric fields show a quadrupolar configura-tion at the West limb • Visible also in extrapolated magnetic fields (PFSS)

  5. (from Barta, Vrsnak & Karlicky, 2007) • Elongated CS becomes unstable via CS tearing The CME propagation may induce reconnection in the lateral streamer CS → outflows! Streamer CS reconnection • Some CME models (as the magnetic breakout model by Antiochos, Lynch, MacNeice et al.) requires a quadru-polar magnetic configuration. • The two CS reconnection model (Zhang, Wang, Hu) considers a flux rope coexisting with two CS, a vertical one below it and a transverse one above it. (from Zhang, Wang & Hu, ApJ 2006)

  6. By measuring densities and geometrical properties of CSs from WL the rec. rate Min can be estimated CS seen in LASCO (from M. Aschwanden, Springer 2004) Basic 2D models for magnetic reconnection: 1) Sweet-Parker: , SLOW; 2) Petschek: , FAST(3 orders of mag. faster) For both models:

  7. qdown d D qup 2) From LASCO/C2 images we measured various CS geometrical properties • At earlier times CS reconnection is Petscheck-tipe with • Reconnection rate decreases with time; reconn. • region elongates towards a Sweet-Parker-tipe. The CS reconnection rate 1) From daily LASCO/C2 pB images we computed densities ne along different radials inside and outside coronal structures → average ne(in) / ne(out) ~ 2 What happened at earlier times?

  8. UVCS slit Slit center • Line intensities show mainly the south- • ward streamer: apparently no significant • intensity variations. • Average subtracted line intensities reveal a much more complicate evolution • What is their interpretation? UVCS observations • Slit center: 35°S (latitude interval: 3°N – 64°S) • Spatial resolution: ~ 3·104 km • Time interval: 10/12, 08:29 → 11/12, 07:33 UT (23 hours) • Time resolution: 2 min • Detected spectral lines:Ly-b, Ly-g and lines from OVI, SiXII, AlXI ions. • SiXII and AlXI lines due only to collisional ex. → • OVI and H lines due both to radiative and collisional excitation • → (Doppler dimming)

  9. UVCS slit field of view CME core? Two converging features CME front Interpretation:during the CME transit in the UVCS field of view we observe inflows towards the reconnecting streamer CS UV line intensity evolution From OVI line intensity we identify: 1) CME front 2) CME core (?) 3) Two converging features inside the southward streamer First direct observation in UVCS!

  10. INFLOW h >> h h , CS cl an CS properties at UVCS CS thickness INFLOW From the inclination of OVI converging features: vin = 3 – 4 km/s • The CS reconnection rate is From the h vs t curve of the X point extrapolated at UVCS vout= 16 km/s • The CS magnetic diffusivity is From the width of the post-reconne-ction feature d= 105 km m2s-1 For comparison: Related to turbulence in the tearing CS (hyperresistivity)? (J. Lin 2007)

  11. Knowing vout, L, Robs we computed ne= ne(Te) curves. Given ne(Te), we derive Tethat better reproduce the observed I(SIXII) and I(AlXI) Pre-rec Main Rec CS physical parameters From UV line intensities we estimate neusing the ratio technique: from where OVI OVI Sixii 10·Alxi Alxi Sixii • Density in pre-reconnection CS is ~ 2 • larger than in the surrounding corona • CS density increases with time by a • factor ~2.6 during reconnection • Temperature increases by ~50%

  12. Summary • The December 10, 2005 CME occurred in a quadrupolar background corona: outflows are associated along north- and southward streamers. • We interpreted outflows as a consequence of reconnection along the streamer CS induced by the CME. • From LASCO data: evolution of reconnection rate, transition from Petschek to Sweet-Parker regime. • From UVCS data: first detection of magnetic reconnection in UVCS; CS diffusivity much larger than expected (hyperresistivity?). • During reconnection the CS to corona density contrast increases by ~2.6, temperature increases by 50%.

  13. This interpretation is confirmed by extrapolating LASCO h vs t curves down to UVCS altitudes

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