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Winter Sun

Winter Sun. Новые направления в физике больших солнечных вспышек. My friend Eric. С.И. Безродных, Л.С. Леденцов, Б.В. Сомов Отдел физики Солнца. ISR, Febr 8 , 2009. Analytical models of magnetic reconnection

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Winter Sun

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  1. Winter Sun

  2. Новые направления в физике больших солнечных вспышек My friend Eric С.И. Безродных, Л.С. Леденцов, Б.В. Сомов Отдел физики Солнца ISR, Febr 8, 2009

  3. Analytical models of magnetic reconnection • Coronal hard X-ray (HXR) sources and particle acceleration

  4. Analytical Models of Magnetic Reconnection Bezrodnykh, Vlasov, Somov, Astronomy Lett. 33, 130, 2007; Astronomy Lett., submitted, 2009; Ledentsov, Somov, Vestnik MGU, in press, 2010

  5. Two classic models of reconnection Current layer by Syrovatskii: direct current (DC) and return currents (RC) inside thin current layer Petschek Flow: compact diffusion regionDand4 attached MHD slow shock waves of infinite length

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

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

  8. Another numerical experiment:MHD shock wave structure in supersonicreconnection Shimisu, Kondo, Ugai. 2005

  9. Attempt interpretation • Aslowshockassociatedwithreconnectionisseparatedbyafastshockintoaswitchoffshock (Region 2) andaslowshock (Region 3) • Theslowshocksformedaroundtheplasmoidisstudied

  10. New analytical solution • 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.

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

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

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

  14. Magnetic field lines

  15. Anglesθ1and θ2 as a function of l Trans-Alfvenic Shock Wave

  16. 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

  17. New consequencesfor 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

  18. The current-layer rupture in a place of anomalous resistivity of plasma Токовый слой с разрывомсодержит области прямого тока DC и присоединенные области обратного тока RC Магнитное поле Аналитическая функция Токовая конфигурацияиз распадающегося слоя Г и четырех присоединенных разрывных течений Sk

  19. Bezrodnykh, Vlasov, Somov, Astronomy Lett., subm., 2009 Generalized analytical model Magnetic field lines in the vicinity of a disrupted current layer with attached discontinuous MHD flows

  20. Coronal HXR Sources andParticle Acceleration Bogacheev and Somov, Astronomy Lett. 33, 54, 2007; 35, 57, 2009; Somov, Astronomy Lett., 36, No. 6, 2010

  21. Main phase limb Chromospheric ribbons

  22. Another flare with a coronal HXR sources • HXRs show • Footpoints • Sources in corona The flare skeleton

  23. Magnetic reconnection interpretation • Release of magnetic energy • Accelerated electrons produce HXRs and heat plasma • RHESSI provides the first pieces of quantitative evidence for reconnectionin flares. reconnection reconnection downflow e- evaporation HXRfootpoints

  24. Quantitative evidence of reconnection Temperature gradient towards the super-hot turbulent-current layer(SHTCL, Somov, 2006) footpoints temperature increase 10-12 keV 8-10 keV 12-14 keV 14-16 keV 16-20 keV 12-14 keV Sui, Holman, 2003

  25. Conclusion from Observations and Theory HXR emissions in flares can be interpreted involving a reconnecting super-hot turbulent-current layeras the source of flare energy Somov B.V., Plasma Astrophysics, Part II, Reconnection and Flares, Springer, 2007 …formulae in these books

  26. New Observational Fact –Downward Motion of Coronal HXR Source Sui and Holman, ApJ 596, L251, 2003; Liu and Gan, ApJ 639, L137, 2005; Ji, Huang, Wang et al., ApJ 636, L173, 2006

  27. GOES and RHESSI light curves of the M7.6 flare on 24 October 2003 Joshi, Veronig, Cho et al., ApJ 706, 1435, 2009

  28. Downward (~11 min, ~15 km/s) and upward (later on) motion of the coronal HXR source Joshi, Veronig, Cho et al., ApJ706, 1435, 2009

  29. Rainbow Reconnection • (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

  30. Rainbow Reconnection • A separator Xappears above the S -bend of the photospheric neutral line NL Somov B.V.: 1985, Soviet Phys. Usp. 28, 271

  31. Vortex flow generates two components of the velocity field in the photoshere y x C – central part • The perpendicularcomponent of velocity drives reconnection in the corona • The parallel component provides a shear of magnetic field above the photosphericNL

  32. Pre-flare Energy Accumulation • (a) An initial configuration • (b) Converging flows induce a reconnecting current layer (RCL) in the corona • An excess energy is stored as magnetic energy of the RCL Somov, Kosugi, Hudson et al., ApJ 579, 863, 2002

  33. Reconnection an Energy Release • Motion of the HXR footpointsdue to reconnection • Footpoint separation increases with time • The apparent displacement is proportional to the reconnected flux

  34. Pre-flare Structure with Shear • (a) The initial configuration • (b) The converging flows creates the RCL • Shear flows make the field lines longer, increasing the energy in magnetic field

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

  36. The rainbow reconnection modelpredicts two types of motionsof chromosphericHXR kernels • An increase of a distance between the ribbons, in that the HXR kernels appear, via reconnection in the RCL • A decrease of the distance between the kernels because of the shear relaxation

  37. The rainbow reconnection modelexplains the descending motionof the coronal HXR source during the early rise phase • A decrease of the distance between the kernels because of the shear relaxation • Downward motion of coronal source Somov, Astronomy Lett. 36, No. 6, 2010

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

  39. 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

  40. 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

  41. 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, No. 6, 2010

  42. Thanksforyourattention 254 years somov@sai.msu.ru

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