Winter Sun

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

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

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

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

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

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

Another numerical experiment: MHD shock wave structure in supersonic reconnection Shimisu, Kondo, Ugai. 2005

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

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.

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

Solution of the problem Unknown function is determined as where

Parameter General solution

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

Magnetic field lines

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

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

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

The current-layer rupture in a place of anomalous resistivity of plasma Токовый слой с разрывом содержит области прямого тока DC и присоединенные области обратного тока RC Магнитное поле Аналитическая функция Токовая конфигурация из распадающегося слоя Г и четырех присоединенных разрывных течений S k

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

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

Main phase Chromospheric ribbons limb

Another flare with a coronal HXR sources HXRs show 1) Footpoints 2) Sources in corona The flare skeleton

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

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

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

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

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

Downward (~11 min, ~15 km/s) and upward (later on) motion of the coronal HXR source

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

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

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

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

Reconnection an Energy Release ► Motion of the HXR footpoints due to reconnection ► Footpoint separation increases with time ► The apparent displacement is proportional to the reconnected flux

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

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

The rainbow reconnection model predicts two types of motions of chromospheric HXR 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

The rainbow reconnection model explains the descending motion of 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

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.

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

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

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

Thanks for your attention 254 years