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Solar Flare Physics Solar Flare Physics
B.V. SomovSolar Physics Department
Astronomical InstituteMoscow State
University
Logic of the talkLogic of the talk
►Apparent motions and real flows Apparent motions and real flows of plasma in flaresof plasma in flares
►Plasma flows in a flare energy Plasma flows in a flare energy sourcesource
►Flows in a surrounding plasmaFlows in a surrounding plasma
Two Classical Models Two Classical Models of of
Solar FlaresSolar Flares
►Standard models Standard models (Carmichael, (Carmichael, 1964; Sturrock, 1966; …)1964; Sturrock, 1966; …)
►Topological models Topological models (Sweet, 1969; (Sweet, 1969; … Gorbachev and Somov *, 1989; … Gorbachev and Somov *, 1989; …)…)
* Gorbachev V.S., Somov B.V., Soviet Astron. -- AJ, * Gorbachev V.S., Somov B.V., Soviet Astron. -- AJ, 3333, , 57, 198957, 1989
What is reconnection in vacuum ?What is reconnection in vacuum ?
The magnetic field of two parallel currents The magnetic field of two parallel currents II ► (a) The initial state, (a) The initial state, 2l2l is a distance between is a distance between
the currentsthe currents► (b) The final state after the currents have (b) The final state after the currents have
been drawn nearer by a dispacement been drawn nearer by a dispacement ll
Reconnection in vacuum is a real Reconnection in vacuum is a real physical processphysical process
► Magnetic field lines move to the X-type Magnetic field lines move to the X-type neutral pointneutral point
► The The electric fieldelectric field is induced and is induced and acceleratesaccelerates particles particles
Reconnection in PlasmaReconnection in Plasma
► (a) The initial state(a) The initial state► (b) The (b) The pre-reconnection statepre-reconnection state with with
a current layer (CL)a current layer (CL)► (c) The final state after reconnection(c) The final state after reconnection
Basic Standard Model of a Two-ribbon FlareBasic Standard Model of a Two-ribbon Flare
► (a)(a) An initial state: a region An initial state: a region AA of a high of a high resistivityresistivity
► (b)(b) Reconnection at the Reconnection at the XX-point -point ► (c)(c) Separation of footpoints Separation of footpoints P P aa and and P P bb
increases as new field lines reconnect increases as new field lines reconnect
Real flows of plasma Real flows of plasma
Apparent displacements of Apparent displacements of
reconnected loop footpointsreconnected loop footpoints
Topological models Topological models **
►Rainbow reconnection model Rainbow reconnection model ►Photospheric plasma flowsPhotospheric plasma flows►Pre-flare energy accumulationPre-flare energy accumulation►Reconnection and energy releaseReconnection and energy release►Apparent and real motions Apparent and real motions ►Downward motion of coronal plasmaDownward 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
Rainbow Reconnection ModelRainbow Reconnection Model
► (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
vortex
Rainbow Reconnection in the CoronaRainbow Reconnection in the Corona
► 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 Physics 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 in a central part in a central part CC
► (b) (b) ConvergingConverging flows induce a flows induce a slowlyslowly reconnecting current layer (RCL ) reconnecting current layer (RCL )
► 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
Converging flows
PhotosphereC
Reconnection and Energy ReleaseReconnection and Energy Release
► The apparent motion The apparent motion of the of the footpoints due to reconnection footpoints due to reconnection
► Footpoint separation increases Footpoint separation increases with timewith time► The apparent displacement is The apparent displacement is
proportionalproportional to a reconnected flux to a reconnected flux
Photospheric flows
Pre-flare Structure with ShearPre-flare Structure with Shear
► (a) The initial configuration (a) The initial configuration ► (b) (b) 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
C
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 separation Rapidly decreasing footpoint separation because of shear relaxationbecause of shear relaxation
Somov, Kosugi, Hudson et al., ApJ, 579, 863, 2002
Shear flow
Shear relaxation
Upward motion
of plasma
The The rainbow reconnection rainbow reconnection modelmodelpredicts predicts two typestwo types of motions of of motions of
chromospheric footpoints (kernels) chromospheric footpoints (kernels)
►An An increaseincrease of a distance between of a distance between the ribbonsthe ribbons, in that the kernels appear, , in that the kernels appear, via 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 reconnectionrainbow reconnectionalso explains also explains
the the descendingdescending motion motionof coronal plasma of coronal plasma
during the early phase of a flare during the early phase of a flare
►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 plasma motion of coronal plasma
Somov, Astronomy Lett. 36, No. 7, 2010
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
Plasma flows in the source of energyPlasma flows in the source of energy
Observational problem Observational problem No. 1No. 1
We do not see We do not see
the primary source of the primary source of
energy release energy release
in a solar flarein a solar flare
RHESSI: Temperature distribution near the RHESSI: Temperature distribution near the source of energysource of energy
14-16 keV
12-14 keV
10-12 keV8-10
keV12-14 keV
16-20 keV
footpoints
Sui, Holman, 2003
How can we observe the super-hot super-hot turbulent-turbulent-current layer current layer (SHTCL,Somov, 2013) ?
temperature increase
Thanks to S. Krucker Shibata 1998
Magnetic reconnection interpretationMagnetic 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-
evaporation
reconnection
reconnection downflow
Shibata 1998
Acceleration Acceleration in a Collapsing Trapin a Collapsing Trap
► A magnetic trap A magnetic trap between the between the Super-Super-Hot Turbulent-Hot Turbulent-Current Layer Current Layer (SHTCL)(SHTCL) and a Fast and a Fast Oblique Collisionless Oblique Collisionless Shock (FOCS) above Shock (FOCS) above magnetic obstacle magnetic obstacle (MO) (MO)
Somov B.V. and Kosugi T., ApJ 485, 859, 1997
Topological Model for theTopological Model for theBastille-day FlareBastille-day Flare
► The SOHO MDI The SOHO MDI magnetogram obtained magnetogram obtained on July 14 for the active on July 14 for the active region NOAA 9077region NOAA 9077
► Model magnetogram Model magnetogram with 5 effective sources with 5 effective sources of magnetic field of magnetic field
Topological portrait and Topological portrait and the field lines forming the field lines forming
the separatricesthe separatrices
► Locations and Locations and shapes of the shapes of the chromospheric chromospheric ribbons predicted ribbons predicted by the topological by the topological modelsmodels
► The TRACE image The TRACE image of the flare at 171 of the flare at 171 A A
Somov, B.V., Oreshina, I.V., Lubimov, G.P., Astronomy Reports, 48, 246, 2004
► Topological model allows Topological model allows to calculate the to calculate the magnetic flux magnetic flux reconnectedreconnected at the at the separator and separator and electric electric fieldfield E1 = 30 V/cm E1 = 30 V/cm
Somov, B.V., Oreshina, I.V., Lubimov, G.P., Astronomy Reports, 48, 246, 2004
Plasma flows near a Super-Hot (Te > or ~ 100 Plasma flows near a Super-Hot (Te > or ~ 100 MK) Turbulent-Current Layer (SHTCL)MK) Turbulent-Current Layer (SHTCL)
Powerful heating Powerful heating of electrons results of electrons results from wave-particle interactions from wave-particle interactions
Somov, 2013, Plasma Astrophysics, Part II, Reconnection and Flares,
Second Edition, Springer SBM, New York
Inflow
Outflow
Outflow
Inflow
Dissipative MHD numerical modeling downflow
Yokoyama, Shibata, ApJ, 474, L61
Magnetic obstacle
Numerical experimentNumerical experiment
MHD shock wave structure in MHD shock wave structure in supersonic reconnectionsupersonic reconnection
Upward Flow
Shimisu, Kondo, Ugai. Shimisu, Kondo, Ugai. 20052005
Upward direction
Resistive MHD Simulations Resistive MHD Simulations of Reconnectionof Reconnection
Upward Flows
Zenitani, Hesse, KlimasZenitani, Hesse, Klimas, , 20102010
Reconnection of open magnetic field lines upward
Diamond-chain Diamond-chain structure related to structure related to excitation of TAS-excitation of TAS-WavesWaves
►The post-plasmoid vertical shocks The post-plasmoid vertical shocks and the and the diamond-chaindiamond-chain structure structure are discovered.are discovered.
►Different resistivity models are Different resistivity models are examined, which showed different examined, which showed different system evolutions.system evolutions.
►However …However …
Old and New Old and New **Analytical Models Analytical Models
of of Magnetic ReconnectionMagnetic Reconnection
*) Bezrodnykh, Vlasov, Somov,*) Bezrodnykh, Vlasov, Somov, Astronomy Lett.Astronomy Lett. 37 37,, 113 113, 201, 20111..
Ledentsov, Somov,Ledentsov, Somov, Astronomy Lett. 37, 131, 201Astronomy Lett. 37, 131, 20111
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
New analytical modelsNew analytical models
►Thin current layer of the Syrovatskii Thin current layer of the Syrovatskii type type andand attached discontinuous 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. 37, Bezrodnykh, Vlasov, Somov, Astronomy Lett. 37, 113, 2011113, 2011
Magnetic field lines
Angles θ1 and θ2 as a function of 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 attached from the Petschek model, the attached discontinuities appear to be not the discontinuities appear to be not the slow MHD but slow MHD but Trans-Alfvenic shock Trans-Alfvenic shock waves (TASW)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 ***) MHD discontinuities in solar flares: *) MHD discontinuities in solar flares: Continuous transitions and plasma heating. Continuous transitions and plasma heating. Ledentsov, today 18:00 Ledentsov, today 18:00
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
What does follow from the What does follow from the theory?theory?
Thermal and non-thermal XR emissions from the corona can be interpreted involving a reconnecting super-hot turbulent-super-hot turbulent-current layer 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
Man
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Heat-transfer problem Heat-transfer problem Predictions for observations (Classical and relaxed heat conduction)
What has to be What has to be understood?understood?
Fe XXVICa XIXFe XXV Ni XXVII
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Many
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Flows in a surrounding plasmaFlows in a surrounding plasma
Plasma flows near a Reconnecting Plasma flows near a Reconnecting Current Layer (RCL): Strong magnetic Current Layer (RCL): Strong magnetic field approximation field approximation (Kolesnikov et al.)(Kolesnikov et al.)
*) Kolesnikov et all. *) Kolesnikov et all.
Chromospheric evaporationChromospheric evaporation
Impulsive heating of plasma Impulsive heating of plasma
by by
energetic electronsenergetic electrons
! T! Tee >> T >> Tp p ! !
► ““Lazy” models – Beam heats electrons and Lazy” models – Beam heats electrons and ionsions
Te
Ti
Energy of
beamTe = Ti = T
► ““Lazy” model – Beam heats electrons and Lazy” model – Beam heats electrons and ionsions
► Real heating Real heating
Te
Ti
Te = Ti = T
Te = 2 T
Ti = 0
F real = eTe ~ Te x Te ~ Te ~ 2 T ~ 10 F lazy
5/2 7/2 7/2 7/2
The “lazy” one-temperature models The “lazy” one-temperature models
of chromospheric evaporationof chromospheric evaporation
are less (10 times) dynamic then are less (10 times) dynamic then
the realistic two-temperature the realistic two-temperature modelsmodels
Instead of ConclusionInstead of Conclusion
In fact, we may proceed In fact, we may proceed with with confidence confidence from simplified models to from simplified models to constructing the more quantitative constructing the more quantitative theory of magnetic reconnection, theory of magnetic reconnection, particle acceleration particle acceleration by reconnection by reconnection and collapsing trapsand collapsing traps, to , to predictionprediction of large flares. of large flares.
