1. Observations on Current Sheet and Magnetic Reconnection in Solar Flares Haimin Wang and Jiong Qiu BBSO/NJIT

2. Background  Magnetic reconnection at low corona is the drive of flares. Recent observations have provided indirect evidence of magnetic reconnection as depicted by the standard (eruptive) flare model.  The rate of magnetic reconnection may be derived from flare observations using sound assumptions and approximations.  Current sheet is the most important structure in the magnetic reconnection process.

3. How do scientists “observe” magnetic Reconnection and Current Sheet, the driver of solar flares?

4. “observe” magnetic reconnection in a standard flare configuration (Courtesy of Terry Forbes )

5. flare loop arcade and two ribbons in EUV TRACE Fe 19.5nm

6. two-ribbon flare observed in different wavelengths

7. YohkohSoHORHESSI Loop-top hard X-ray source (Masuda et al. 1994) and super-hot source (Tsuneta 1997) High-temperature structure indicative of current sheet (Ko et al. 2003) Hard X-ray sources at two ends of RCS (Sui et al. 2003). High temperature ridges along outer loops (Tsuneta 1996) Evidence of chromospheric evaporation (Czaykowska et al. 1999) Soft X-ray jets (Shimizu 1994, 1995) Signatures of magnetic reconnection and Current sheet in the corona: satellite observations

8. Here put a couple of figures from satellite Observations. Masuda flare: hard X-ray source above the loop top (Masuda et al. 1994) YOHKOH

9. soft X-ray jet as indication of reconnection outflow (Shimizu 1994) soft X-ray high temperature ridges along outer or newly formed loops (Tsuneta 1996) YOHKOH

10. high temperature structure indicative of current sheet (Ko et al. 2003) X-ray sources at two ends of current sheet (Sui et al. 2003)   SOHO RHESSI

11. The rate of magnetic reconnection can be inferred from some sorts of observations using sound assumptions and approximations.

12. Magnetic reconnection is the driver of solar flares.  Magnetic reconnection rate is deduced by measuring expansion of flare ribbons across magnetic fields.  E field corona surface

13. Physical approach : Forbes & Lin (2000) Ec: electric field along the reconnecting current sheet (RCS) at the corona V 11 l

14. M1.0 flare on 2000 September 12

15. Ribbon 1 Ribbon 2 electric field (V/cm) voltage drop (Mx/s)

16. magnetic reconnection rate and flare emission 11 12 13 14 hr.8.6.4.2.0 4321043210 flare soft X-ray emission rate E field (V/cm) flux rate (1e+18 Mx/s)

17. X1.6 flare on 2001 October 19

18. Electric field (v/cm) Voltage drop (Mx/s) Ribbon 1 Ribbon 2

19. flux rate (1e+18 Mx/s) 16:20 16:30 16:40 16:50 17:00 E field (V/cm) flare microwave emission at 10 GHz 64206420 7.5 5.0 2.5 0.0 Magnetic reconnection rate and flare non-thermal emission

20. rate of total magnetic flux reconnected E field flare flux rate E field flare Either way, it evolves along with flare high-energy emission. two ways to measure the magnetic reconnection rate 11 12 13 14 16:10 16:20 16:30 16:40 16:50 17:00 event 1 event 2 7.5 5.0 2.5 0.0 0.8 0.4 0.0

21. They are all driven magnetically. Coronal mass ejections are often accompanied by filament eruptions and flares.

22. correlation between mass flight and flare emission (Zhang et al. 2001)  CME flare  In some flare-CME events, acceleration of CMEs and magnetic reconnection that drives flares are closely related.

23. (Lin et al. 2004) CME filament two-ribbon flare A schematic flux rope model for CME and flare

24. mass acceleration magnetic reconnection flare emission

25. Strong Correlation Between Magnetic Reconnection Rate and Filament Acceleration (Jing et al., 2004, Ap.J. to be submitted)

26. Weaker Correlation Between Magnetic Reconnection Rate and CME Acceleration (Jing et al., 2004, Ap.J. to be submitted)

27. The derived magnetic reconnection rate is temporally correlated with flare non-thermal emission and mass acceleration of core flux rope ejection.

28. SUMMARY Indirect Evidence of Current Sheets and Magnetic Reconnection High temperature region in Helmet Structure Plasma outflow above flare loop Loop top HXR source Organized separation of flare ribbons