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INITIATION AND EVOLUTION OF CORONAL SHOCK WAVES

INITIATION AND EVOLUTION OF CORONAL SHOCK WAVES. B. Vršnak, T. Žic , S. Lulić ( Hvar Obs .) N. Muhr , A. Veronig , M. Temmer , I. Kienreich ( Uni.- Graz ). This work has been supported in part by Croatian Scientific Foundation

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INITIATION AND EVOLUTION OF CORONAL SHOCK WAVES

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  1. INITIATIONAND EVOLUTIONOFCORONAL SHOCK WAVES B. Vršnak, T. Žic, S. Lulić (Hvar Obs.) N. Muhr, A. Veronig, M. Temmer, I. Kienreich (Uni.-Graz) This work hasbeensupportedinpartbyCroatianScientificFoundation underthe project 6212 „SolarandStellarVariability“ (SOLSTEL).

  2. Observational signatures • Type II radio bursts (Wild & McCready 1950, Aust.J.Phys. 3, 387) • Moreton waves (Moreton & Ramsey 1960, PASP 72, 357) KSO

  3. NRH EUV, SXR, HeI, coronograph, radio,... Yohkoh EIT/SoHO MLSO

  4. Domain / Signature in situ IP (radio, WL) Low Corona (EUV) Corona - radio type II - WL fronts, streamers Upper Chromosphere & TR (Ha, HeI, …) Moreton, disturbed filaments, … timing, kinematics, intensity,spectral, morphology, …

  5. Terminology piston shock bow shock

  6. w w u u vA0 xf x Large-amplitude wave (shock) • impulsive plasma motion perpendicular to the magnetic field ("strong" acceleration) • large amplitude wavefront is created • shock forms after certain time/distance due to the nonlinear evolution of the perturbation (signal velocity depends on the amplitude!) w(t) = w0 + k u(t) k=4/3, w0=cs0 at b >> 1 k=3/2, w0=vA0 at b << 1

  7. PistonMechanism (simulations) 1D - planar wave piston • - amplitude growth + steepening shockformation • after t~0.15 ~const. amplitude/velocity 2D - cylindrical dip • amplitude growth + steepening  shock formation • - lower amplitude, formation of rarefaction region • after t~0.08 decreasing amplitude/velocity

  8. Waveevolution (2D)

  9. 2.5-D MHD simulation + By Bz Bf b = 0

  10. MHD simulation: Corona (horizonatal) wave 0.2 0.1 0.08 piston • steepening + ampl. increaseshock • - deceleration; ampl. decrease • corona/Moretonoffset • corona/Moretondelay 0.2 0.1 0.08 piston

  11. MHD simulation: Corona (above) contact surface “standing” shock streamer (currentsheet) (reconnectionoutflowjet) fast-mode standingshock

  12. comparisonwithanalytical: • v2w = const.; • cs = 10 km/s = const. MHD simulation: Moretonwave

  13. Conclusion • upward (type II burst) = driven bow/piston shock • lateral (EUV, HeI, Ha) = temporary piston (“CME overexpansion”) • the time/distance of the shock formation and its amplitude/speed depend strongly on the impulsiveness of the piston • Moreton wave appears only if shock is sufficiently strong (fast); only the upper chromosphere is affected • downward propagating chromospheric disturbance is quasi-longitudinal fast-mode shock that can be well approximated by a sound shock • Moreton wave lags behind the coronal wave due to chromospheric inertia

  14. Thankyoufor yourattention

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