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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 sources and particle accelerationacceleration
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 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: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 prescribed but determined from a self-but determined from a self-consistent solutionconsistent 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 Despite the expectations that follow from the Petschek model, follow from the Petschek model, the attached discontinuities appear the attached discontinuities appear to be not the slow MHD but to 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 New possibilities to interpret results of results of numerical and numerical and laboratory experiments laboratory experiments on on reconnection in the dissipative reconnection in the dissipative MHD and collisionless plasmasMHD 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 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 ……form
ulae in th
ese books
formulae in
these b
ooks
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
