1. SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad “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

2. SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad The January 10-11, 2005 CME (LASCO/C2 images) (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 R ʘ )=320 km/s Accelerating: a ~ 4.5 m/s 2 During/after the event: Outflows along two lateral streamers UVCS slit

3. SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad 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. SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad (from http://ccmc.gsfc.nasa.gov/ ) The magnetic configuration East limb West limb CME outflow 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) Outflows along streamers possibily induced by the CME propagation. …through which physical processes?

5. SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad Streamer CS reconnection (from Zhang, Wang & Hu, ApJ 2006) 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 Barta, Vrsnak & Karlicky, 2007) Elongated CS becomes unstable via CS tearing The CME propagation may induce reconnection in the lateral streamer CS → outflows!

6. SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad 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: By measuring densities and geometrical properties of CSs from WL the rec. rate M in can be estimated

7. SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad 2) From LASCO/C2 images we measured various CS geometrical properties The CS reconnection rate    down  up 1) From daily LASCO/C2 pB images we computed densities n e along different radials inside and outside coronal structures → average n e (in) / n e (out) ~ 2 What happened at earlier times? At earlier times CS reconnection is Petscheck-tipe with Reconnection rate decreases with time; reconn. region elongates towards a Sweet-Parker-tipe.

8. SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad UVCS observations UVCS slit Slit center: 35°S (latitude interval: 3°N – 64°S) Spatial resolution: ~ 3·10 4 km Time interval: 10/12, 08:29 → 11/12, 07:33 UT (23 hours) Time resolution: 2 min Detected spectral lines: Ly- , Ly-  and lines from O VI, Si XII, Al XI ions. Si XII and Al XI lines due only to collisional ex. → O VI and H lines due both to radiative and collisional excitation → (Doppler dimming) Line intensities show mainly the south- ward streamer: apparently no significant intensity variations. Slit center Average subtracted line intensities reveal a much more complicate evolution What is their interpretation?

9. SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad UV line intensity evolution CME front CME core? Two converging features From OVI line intensity we identify: 1) CME front 2) CME core (?) 3) Two converging features inside the southward streamer UVCS slit field of view Interpretation: during the CME transit in the UVCS field of view we observe inflows towards the reconnecting streamer CS First direct observation in UVCS!

10. SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad CS properties at UVCS From the inclination of O VI converging features: v in = 3 – 4 km/s INFLOW CS thickness From the width of the post-reconne- ction feature  = 10 5 km From the h vs t curve of the X point extrapolated at UVCS v out  = 16 km/s The CS reconnection rate is m 2 s -1 The CS magnetic diffusivity is For comparison: Related to turbulence in the tearing CS (hyperresistivity)? (J. Lin 2007) anclCS , 

11. SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad CS physical parameters From UV line intensities we estimate n e using the ratio technique: from where Knowing v out, L, R obs we computed n e = n e (T e ) curves. Given n e (T e ), we derive T e that better reproduce the observed I(SI XII ) and I(Al XI ) n e (cm -3 )T e (K) Corona 4·10 6 1.2·10 6 Pre-rec 6.5·10 6 1.8·10 6 Rec 7.2·10 6 2.2·10 6 Main 7.6·10 6 2.5·10 6 Pre-rec Rec Main O VI 10 · Al xi Si xii O VI Al xi Si xii 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. SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad 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. SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent SOHO-20 “Transient events on the Sun and In the Heliosphere” – August 28, 2008, Ghent “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad “Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad This interpretation is confirmed by extrapolating LASCO h vs t curves down to UVCS altitudes