The Propagation of Shocks in the Corona

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The Propagation of Shocks in the Corona

• A. Nindos1, C. Alissandrakis1, A. Hilaris2, C.
  Caroubalos3, A. Kerdraon4

1University of Ioannina, Physics Department,
Ioannina, Greece 2University of Athens, Physics
Department, Athens, Greece 3University of Athens,
Department of Informatics, Athens,
Greece 4Observatory of Paris, France
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Type II Radio Bursts

• Produced by electrons accelerated at MHD shocks
• Radio emission slowly drifting bands at ?p
  (fundamental), 2?p (harmonic)
• How and where do shocks develop?
• Flare driven? (blast wave)
• CME driven? (piston-driven) (if yes, from
  which part of the CME?)
  
  
• Close temporal relationship btw flares-CMEs
  creates
• difficulties

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Objective - Data

• In depth study of the properties of shock waves
  in the corona
• Select all Type IIs identified in the 110-687 MHz
  range observations of Artemis spectrograph and
  observed simultaneously w/ the Nancay RH
• Two events will be presented a flare/CME-less
  Type II and a flare/CME-associated Type II.

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Modeling the propagation of the blast wave
Density 2-fold Newkirk model Magnetic field PFSS
Magneto-sonic waves are released at the flares
location
Dashed lines iso-density layers corresponding to
plasma emission at 236 and 164 MHz Gray scale
map of the magneto-sonic speed Solid curves
projections of the wave-fronts Orange and purple
locations of the centroids of the 236 164 MHz
sources
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Arrows indicate the orientation of the magnetic
field
Emission _at_ the location of the iso-density
surfaces where the angle btw the m.f. and the
wave/shock normal is gt 60 deg.
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The simulation explains why the 236 164 MHz
occur simultaneously
The lateral motion of the NRH sources is
consistent w/ the model
The wave reaches the iso-density layers
corresponding to plasma emission at 236 164 MHz
200 s after the initiation of the disturbance
The data show that the Type II starts 230 sec
after the flare onset
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Summary of the March-7-2000 event

• The lateral displacement of the radio sources
  from the location of the flare site is explained
  by the refraction of the wave into regions of low
  m-s speed
• Radio emission comes from restricted regions of
  the wave front where the angle btw m.f. and the
  shock normal large ? quasi-perpendicular regime
• Timing of the event roughly consistent with the
  model

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Expanding loops or Wave?
Huygens plotting to determine the source of the
disturbance (assuming it is a wave)
Result is NOT consistent with the data
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Temporal evolution
Vloops 400 km/s VCME 551 km/s ?t 37 min
(?t ? time interval btw the last SXT loop and the
first appearance of the LASCO CME ?t is large,
LASCO misses CMEs acceleration phase and
discrepancies are unavoidable
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Conclusions

• Two shocks w/ contrasting properties
• CME-less shock Blast wave scenario seems
  appropriate.
• Its properties are explained by the combination
  of refraction of the shock into regions of low
  m-s speed the preferential acceleration of
  electrons in restricted regions of the shock
  (quasi-perp. regime).
• CME/flare-related shock the Type II shock
  related to the early development of the CME

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Vloops 400 km/s VCME 551 km/s ?t 37 min
(?t ? time interval btw the last SXT loop and the
first appearance of the LASCO CME In its first
appearance the CME front is located at h 1800
above the limb With a 0, ?t 37 min ? h
1337 With a 16 m/s2 (CMEs acceleration),
?t 2200 s ? h 1391 But the data miss the
CMEs impulsive acceleration phase