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

►Analytical models of magnetic Analytical models of magnetic reconnectionreconnection

►Coronal hard X-ray (HXR) Coronal hard X-ray (HXR) sources and particle accelerationsources and particle acceleration

Analytical Models Analytical Models of of

Magnetic ReconnectionMagnetic Reconnection

Bezrodnykh, Vlasov, Somov, Astronomy Lett. 33, 130, Bezrodnykh, Vlasov, Somov, Astronomy Lett. 33, 130, 2007;2007;

Astronomy Lett., submitted, 2009;Astronomy Lett., submitted, 2009;Ledentsov, Somov, Vestnik MGU, in press, 2010Ledentsov, 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 layerPetschek 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:Another numerical experiment:

MHD shock wave structure in MHD shock wave structure in supersonic reconnectionsupersonic reconnection

Shimisu, Kondo, Ugai. 2005Shimisu, Kondo, Ugai. 2005

Attempt interpretationAttempt interpretation

►AA slow shock associated with slow shock associated with reconnection is separated by a reconnection is separated by a fastfast shock into a shock into a switch offswitch off shock shock (Region 2) and a slow shock (Region 2) and a slow shock (Region 3)(Region 3)

►TThehe slow shocks formed around the slow shocks formed around the plasmoid is studiedplasmoid is studied

New analytical solutionNew analytical solution►Thin current layer of the Syrovatskii Thin current layer of the Syrovatskii

type and attached discontinuous type and attached discontinuous MHD flows of finite lengthMHD flows of finite length

►A character of flows is A character of flows is notnot prescribed but determined from a prescribed but determined from a self-consistent solutionself-consistent solution

►Global structure of magnetic field Global structure of magnetic field and and local local properties of the field near properties of the field near current layer and discontinuitiescurrent 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

GeometricGeometrical al parameterparameters of the s of the modelmodel

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

Magnetic field linesMagnetic field lines

AnglesAngles θ θ11 andand θ θ22 as a function as a function of lof l

Trans-Alfvenic Shock Trans-Alfvenic Shock WaveWave

New features of reconnectionNew features of reconnection►Despite the expectations that follow Despite the expectations that follow

from the Petschek model, the from the Petschek model, the attached discontinuities appear to attached discontinuities appear to be not the slow MHD but be not the slow MHD but Trans-Trans-Alfvenic shock waves (TASW)Alfvenic shock waves (TASW)

►This is typical for the fast This is typical for the fast reconnection with reconnection with return currents return currents inside the current layerinside the current layer

►TASW are TASW are non-evolutionarynon-evolutionary

New consequencesNew consequencesfor physics of solar flares for physics of solar flares

► Two types of transition Two types of transition from non-from non-evolutionary shock waves (TASW) evolutionary shock waves (TASW) to evolutionary ones exist to evolutionary ones exist depending on geometrical depending on geometrical parameters of reconnection regionparameters of reconnection region

►New possibilities to interpret results New possibilities to interpret results of of numerical and laboratory numerical and laboratory experiments experiments on reconnection in the on reconnection in the dissipative MHD and collisionless dissipative MHD and collisionless plasmasplasmas

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 RCМагнитное поле

Аналитическая функция

Токовая конфигурация из распадающегося слоя Г и четырех присоединенных разрывных течений Sk

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 Coronal HXR Sources andand

Particle AccelerationParticle Acceleration

Bogacheev and Somov, Astronomy Lett. Bogacheev and Somov, Astronomy Lett. 3333, 54, , 54, 2007; 2007; 3535, 57, 2009;, 57, 2009;

Somov, Astronomy Lett., 36, No. 6, 2010Somov, Astronomy Lett., 36, No. 6, 2010

Main phase Main phase

Chromospheric ribbons

limb

Another flare with a coronal HXR Another flare with a coronal HXR sources sources

HXRs show1) Footpoints2) Sources in

corona

The flare skeleton

Magnetic reconnection interpretationMagnetic 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-

evaporation

reconnection

reconnection downflow

Quantitative evidence of Quantitative evidence of reconnectionreconnection

14-16 keV

12-14 keV

10-12 keV8-10

keV12-14 keV

16-20 keV

footpoints

Sui, Holman, 2003

Temperature gradient towardsthe super-hot turbulent-current layer (SHTCL,Somov, 2006)

temperature increase

Conclusion from Observations and TheoryConclusion from Observations and Theory

HXR emissions in flares HXR emissions in flares can be interpreted can be interpreted involving a reconnecting involving a reconnecting super-hot turbulent-super-hot turbulent-current layercurrent layer as the as the source of flare energysource of flare energy

Somov B.V., Somov B.V., Plasma Astrophysics, Plasma Astrophysics, Part II, Reconnection and Flares, Part II, Reconnection and Flares, Springer, 2007Springer, 2007 ……formulae in these books

formulae in these books

New Observational Fact –New Observational Fact –

Downward Motion of Downward Motion of Coronal HXR SourceCoronal 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

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 ReconnectionRainbow Reconnection

► (a) A model distribution of magnetic field (a) A model distribution of magnetic field in the photospherein the photosphere

► (b) A (b) A vortex flow vortex flow distorts the neutral line distorts the neutral line so that it takes the shape of the letter so that it takes the shape of the letter SS

Rainbow ReconnectionRainbow Reconnection

► A separator A separator XX appears above the appears above the S S -bend -bend of the photospheric neutral line of the photospheric neutral line NLNL

Somov B.V.: 1985, Soviet Phys. Usp. 28, 271

Vortex flow generates two components of Vortex flow generates two components of the the velocity field in the photosherevelocity field in the photoshere

► The The perpendicularperpendicular component of velocity component of velocity drives drives reconnectionreconnection in the corona in the corona

► The The parallelparallel component provides a component provides a shearshear of of magnetic field above the photospheric magnetic field above the photospheric NLNL

xy

C – central part

Pre-flare Energy AccumulationPre-flare Energy Accumulation

► (a) An initial configuration (a) An initial configuration ► (b) (b) ConvergingConverging flows induce a reconnecting flows induce a reconnecting

current layer (RCL) in the coronacurrent layer (RCL) in the corona► An An excess energy excess energy is stored as magnetic is stored as magnetic

energy of the RCL energy of the RCL Somov, Kosugi, Hudson et al., ApJ 579, 863, 2002

Reconnection an Energy ReleaseReconnection an Energy Release

► Motion of the HXR footpoints due to Motion of the HXR footpoints due to reconnection reconnection

► Footpoint separation increases Footpoint separation increases with timewith time► The apparent displacement is The apparent displacement is

proportionalproportional to the reconnected flux to the reconnected flux

Pre-flare Structure with ShearPre-flare Structure with Shear

► (a) The initial configuration (a) The initial configuration ► (b) The converging flows creates the RCL(b) The converging flows creates the RCL► Shear flows Shear flows make the field lines longer, make the field lines longer,

increasing the energy in magnetic fieldincreasing the energy in magnetic field

Motion of HXR FootpointsMotion of HXR Footpoints

► (a) Pre-reconnection state of the magnetic (a) Pre-reconnection state of the magnetic field with the converging and field with the converging and shearshear flows flows

► (b) (b) Rapidly decreasing footpoint Rapidly decreasing footpoint separation separation because of shear relaxationbecause of shear relaxation

Somov, Kosugi, Hudson et al., ApJ, 579, 863, 2002

The The rainbow reconnection rainbow reconnection modelmodel

predicts predicts two typestwo types of motions of motionsof chromospheric HXR kernels of chromospheric HXR kernels

►An An increaseincrease of a distance between of a distance between the ribbons, in that the HXR kernels the ribbons, in that the HXR kernels appear, via appear, via reconnectionreconnection in the RCL in the RCL

►A A decreasedecrease of the distance between of the distance between the kernels because of the the kernels because of the shear shear relaxation relaxation

The The rainbow reconnection rainbow reconnection modelmodel

explains the explains the descendingdescending motion motionof the coronal HXR source of the coronal HXR source

during the early rise phase during the early rise phase

►A A decreasedecrease of the distance between of the distance between the kernels because of the the kernels because of the shear shear relaxationrelaxation

►DownwardDownward motion of coronal source 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.

HXHHHXHHHXHXX-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 At the time when the collapsing trap has the collapsing trap has the

maximal brightness maximal brightness in HXR, in HXR, the height of the loop-top (LT) the height of the loop-top (LT)

source in the corona is source in the corona is proportional to the distance proportional to the distance

between footpoint (FP) between footpoint (FP) sources sources in the chromosphere 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

ThankThankss for your attention for your attention

254 years

somov@sai.msu.ru