1. Solar Flare Physics B.V. Somov Solar Physics Department Astronomical Institute Moscow State University My friend Eric

2. Logic of the talk ► Apparent motions and real flows of plasma in flares ► Plasma flows in a flare energy source ► Flows in a surrounding plasma

3. Contents ► Two classical models of solar flares ► Downward motion of coronal plasma ► Plasma flows in the source of energy ► Chromospheric evaporation

4. Two Classical Models of Solar Flares ► Standard models (Carmichael, 1964; Sturrock, 1966; …) ► Topological models (Sweet, 1969; … Gorbachev and Somov *, 1989; …) * Gorbachev V.S., Somov B.V., Soviet Astron. -- AJ, 33, 57, 1989

5. What is reconnection in vacuum ? The magnetic field of two parallel currents I ► (a) The initial state, 2l is a distance between the currents ► (b) The final state after the currents have been drawn nearer by a dispacement  l

6. Reconnection in vacuum is a real physical process ► Magnetic field lines move to the X-type neutral point ► The electric field is induced and accelerates particles

7. Reconnection in Plasma ► (a) The initial state ► (b) The pre-reconnection state with a current layer (CL) ► (c) The final state after reconnection

8. Basic Standard Model of a Two-ribbon Flare ► (a) An initial state: a region A of a high resistivity ► (b) Reconnection at the X-point ► (c) Separation of footpoints P a and P b increases as new field lines reconnect

9. Real flows of plasma Apparent displacements of reconnected loop footpoints

10. Topological models * ► Rainbow reconnection model ► Photospheric plasma flows ► Pre-flare energy accumulation ► Reconnection and energy release ► Apparent and real motions ► Downward motion of coronal plasma *) Reviewed in Somov B.V., Plasma Astrophysics, Part II, Reconnection and Flares, Second Edition, Springer SBM, New York, 2013, Chapters 4 - 7

11. Rainbow Reconnection Model ► (a) A model distribution of magnetic field in the photosphere ► (b) A vortex flow distorts the neutral line so that it takes the shape of the letter S vortex

12. Rainbow Reconnection in the Corona ► A separator X appears above the S -bend of the photospheric neutral line NL Somov B.V.: 1985, Soviet Physics Usp. 28, 271

13. Vortex flow generates two components of the velocity field in the photoshere ► The perpendicular component of velocity drives reconnection in the corona ► The parallel component provides a shear of magnetic field above the photospheric NL x y C – central part

14. Pre-flare Energy Accumulation ► (a) An initial configuration in a central part C ► (b) Converging flows induce a slowly reconnecting current layer (RCL ) ► An excess energy is stored as magnetic energy of the RCL Somov, Kosugi, Hudson et al., ApJ 579, 863, 2002 Converging flows Photosphere C

15. Reconnection and Energy Release ► The apparent motion of the footpoints due to reconnection ► Footpoint separation increases with time ► The apparent displacement is proportional to a reconnected flux Photospheric flows

16. Pre-flare Structure with Shear ► (a) The initial configuration Shear flows ► (b) Shear flows make the field lines longer, increasing the energy in magnetic field C

17. Motion of HXR Footpoints ► (a) Pre-reconnection state of the magnetic field with the converging and shear flows Rapidly decreasing footpoint separation ► (b) Rapidly decreasing footpoint separation because of shear relaxation Somov, Kosugi, Hudson et al., ApJ, 579, 863, 2002 Shear flow Shear relaxation Upward motion of plasma

18. The rainbow reconnection model predicts two types of motions of chromospheric footpoints (kernels) ► An increase of a distance between the ribbons, in that the kernels appear, via reconnection in the RCL ► A decrease of the distance between the kernels because of the shear relaxation

19. The rainbow reconnection also explains the descending motion of coronal plasma during the early phase of a flare ► A decrease of the distance between the kernels because of the shear relaxation ► Downward motion of coronal plasma Somov, Astronomy Lett. 36, No. 7, 2010

21. Reconnected loops are strongly stressed by magnetic tensions to the edge of RCL Magnetic obstacle Quasi-equilibrium loops: height of a loop is proportional to the distance between its feet.

22. HXHHHX X-ray flux from a collapsing magnetic trap in energy ranges: a – 25 keV, b – 50 keV, c – 75 kev as a function of trap length Bogachev and Somov, Astronomy Lett. 33, 54, 2007

23. At the time when the collapsing trap has the maximal brightness in HXR, the height of the loop-top (LT) source in the corona is proportional to the distance between footpoint (FP) sources in the chromosphere At the time when the collapsing trap has the maximal brightness in HXR, the height of the loop-top (LT) source in the corona is proportional to the distance between footpoint (FP) sources in the chromosphere

24. Rapid decrease of FP separation dominates an increase of distance between flare ribbons FPs separate in opposite directions from PNL and from each other Somov, Astronomy Lett. 36, 514, 2010  y >>  x  y = 0  z < 0  z > 0

25. Plasma flows in the source of energy

26. Observational problem No. 1 We do not see the primary source of energy release in a solar flare

27. RHESSI: Temperature distribution near the source of energy 14-16 keV 12-14 keV 10-12 keV 8-10 keV 12-14 keV 16-20 keV footpoints Sui, Holman, 2003 super-hot turbulent- current layer How can we observe the super-hot turbulent- current layer (SHTCL, Somov, 2013) ? temperature increase Thanks to S. KruckerShibata 1998

28. Magnetic reconnection interpretation 1)Release of magnetic energy 2)Accelerated electrons produce HXRs and heat plasma 3)RHESSI provided the first pieces of quantitative evidence for reconnection in flares. HXR footpoints e-e- evaporation reconnection reconnection downflow Shibata 1998

31. Acceleration in a Collapsing Trap ► A magnetic trap between the Super-Hot Turbulent-Current Layer (SHTCL) and a Fast Oblique Collisionless Shock (FOCS) above magnetic obstacle (MO) Somov B.V. and Kosugi T., ApJ 485, 859, 1997

32. Topological Model for the Bastille-day Flare ► The SOHO MDI magnetogram obtained on July 14 for the active region NOAA 9077 ► Model magnetogram with 5 effective sources of magnetic field

33. Topological portrait and the field lines forming the separatrices

34. ► Locations and shapes of the chromospheric ribbons predicted by the topological models ► The TRACE image of the flare at 171 A Somov, B.V., Oreshina, I.V., Lubimov, G.P., Astronomy Reports, 48, 246, 2004

35. ► Topological model allows to calculate the magnetic flux reconnected at the separator and electric field E1 = 30 V/cm Somov, B.V., Oreshina, I.V., Lubimov, G.P., Astronomy Reports, 48, 246, 2004

36. Calculated temperature distribution

37. Plasma flows near a Super-Hot (Te > or ~ 100 MK) Turbulent-Current Layer (SHTCL) Powerful heating of electrons results from wave-particle interactions Somov, 2013, Plasma Astrophysics, Part II, Reconnection and Flares, Second Edition, Springer SBM, New York Inflow Outflow Inflow

38. Dissipative MHD numerical modeling downflow Yokoyama, Shibata, ApJ, 474, L61 Magnetic obstacle

39. Upflow: «Free upward» reconnection creates magnetic «island» (magnetic obstacle) Heat conduction front moves much faster than slow MHD shock wave

40. Numerical experiment MHD shock wave structure in supersonic reconnection Numerical experiment MHD shock wave structure in supersonic reconnection Upward Flow Shimisu, Kondo, Ugai. 2005

41. Upward direction

44. Resistive MHD Simulations of Reconnection Resistive MHD Simulations of Reconnection Upward Flows Zenitani, Hesse, Klimas, 2010

45. Reconnection of open magnetic field lines upward

46. Diamond-chain structure related to excitation of TAS-Waves

47. ► The post-plasmoid vertical shocks and the diamond-chain structure are discovered. ► Different resistivity models are examined, which showed different system evolutions. ► However …

48. Old and New * Analytical Models of Magnetic Reconnection *) Bezrodnykh, Vlasov, Somov, Astronomy Lett. 37, 113, 2011. Ledentsov, Somov, Astronomy Lett. 37, 131, 2011

49. Two classic models of reconnection Thin current layer by Syrovatskii: direct current (DC) and return currents (RC) inside the current layer Petschek Flow: compact diffusion region D and 4 attached MHD slow shock waves of infinite length

50. New model of reconnection in the presence of attached MHD discontinuities Configuration of currents: Current layer Г and 4 attached discontinuities of finite length The Riemann-Hilbert problem for Magnetic field Analytical function

53. Attempt interpretation ► A slow shock associated with reconnection is separated by a fast shock into a switch off shock (Region 2) and a slow shock (Region 3) ► The slow shocks formed around the plasmoid is studied

54. New analytical models ► Thin current layer of the Syrovatskii type and attached discontinuous MHD flows of finite length ► A character of flows is not prescribed but determined from a self-consistent solution ► Global structure of magnetic field and local properties of the field near current layer and discontinuities Bezrodnykh, Vlasov, Somov, Astronomy Lett. 37, 113, 2011

55. New model of reconnection in the presence of attached MHD discontinuities Configuration of currents: Current layer Г and 4 attached discontinuities of finite length The Riemann-Hilbert problem for Magnetic field Analytical function

56. Solution of the problem Unknown function is determined as where

57. Parameter General solution

58. Geometrical parameters of the model L – halfwidth of current layer (CL) R – length of discontinuity l – coordinate along the discontinuity

59. Magnetic field lines

60. Angles θ 1 and θ 2 as a function of l Trans-Alfvenic Shock Wave

61. New features of reconnection ► Despite the expectations that follow from the Petschek model, the attached discontinuities appear to be not the slow MHD but Trans-Alfvenic shock waves (TASW) ► This is typical for the fast reconnection with return currents inside the current layer ► TASW are non-evolutionary * *) MHD discontinuities in solar flares: Continuous transitions and plasma heating. Ledentsov, today 18:00

62. New consequences for physics of solar flares ► Two types of transition from non- evolutionary shock waves (TASW) to evolutionary ones exist depending on geometrical parameters of reconnection region ► New possibilities to interpret results of numerical and laboratory experiments on reconnection in the dissipative MHD and collisionless plasmas

63. What does follow from the theory? super-hot turbulent-current layer Thermal and non-thermal XR emissions from the corona can be interpreted involving a reconnecting super-hot turbulent-current layer as the source of flare energy Somov B.V., Plasma Astrophysics, Part II, Reconnection and Flares, Second Edition, Springer SBM, New York, 2013 Many formulae if you like them Heat-transfer problem Heat-transfer problem  Predictions for observations (Classical and relaxed heat conduction) What has to be understood? Fe XXVI Ca XIX Fe XXV Ni XXVII Many formulae if you like them

64. Flows in a surrounding plasma Plasma flows near a Reconnecting Current Layer (RCL): Strong magnetic field approximation (Kolesnikov et al.) *) Kolesnikov et all.

65. Chromospheric evaporation Impulsive heating of plasma by energetic electrons ! T e >> T p !

66. ► “Lazy” models – Beam heats electrons and ions TeTe TiTi Energy of beam T e = T i = T

67. ► “Lazy” model – Beam heats electrons and ions ► Real heating TeTe TiTi T e = T i = T T e = 2 T T i = 0 F real =  e  T e ~ T e x T e ~ T e ~ 2 T ~ 10 F lazy 5/2 7/2 7/2 7/2

68. The “lazy” one-temperature models of chromospheric evaporation are less (10 times) dynamic then the realistic two-temperature models

69. Instead of Conclusion In fact, we may proceed with confidence from simplified models to constructing the more quantitative theory of magnetic reconnection, particle acceleration by reconnection and collapsing traps, to prediction of large flares.

70. Thanks for your attention 260 years somov@sai.msu.ru 1755