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MHD modeling of coronal disturbances related to CME lift-off

MHD modeling of coronal disturbances related to CME lift-off J. Pomoell 1 , R. Vainio 1 , S. Pohjolainen 2 1 Department of Physics, University of Helsinki 2 Tuorla Observatory, University of Turku. jens.pomoell@helsinki.fi. Introduction.

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MHD modeling of coronal disturbances related to CME lift-off

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  1. MHD modeling of coronal disturbances related to CME lift-off J. Pomoell1, R. Vainio1, S. Pohjolainen2 1Department of Physics, University of Helsinki 2Tuorla Observatory, University of Turku jens.pomoell@helsinki.fi

  2. Introduction • Solar flares and coronal mass ejections (CMEs) capable of launching global large-amplitude coronal disturbances and shocks • Observed directly in Hα (Moreton waves), EUV (EIT waves), soft X-rays, He I and radio STEREO AHEAD EUVI 195 Å May 19, 2007 • Play a role in the acceleration of electrons and ions to high energies, exact mechanisms unclear • Observed in-situ and as various EM signatures

  3. Type II radio bursts • Plasma emission (F+H) caused by shock-accelerated e- • , knowing gives

  4. Questions & Aims • Current consensus: Interplanetary type IIs generated by CME driven shocks. But what about coronal type IIs, generated by blast waves (flares) or driven waves (CMEs)? or ? • What about high-frequency type IIs? • We address such issues by performing MHD simulations of CME lift-off • Look for features that might be of importance when interpreting observations (Pohjolainen, Pomoell, Vainio: A&A 490, 2008)

  5. MHD Model • 2D model, gravitationally stratified corona including a dense loop • Superimpose flux rope structure with higher density • Alfvén speed increases in the higher corona, low in the loop

  6. Eruption dynamics Density Speed • When the flux rope starts to rise, a perturbation is formed around the flux rope, and steepens to a shock • Below the loop, the shock remains weak, but strengthens and slows down quickly when entering the loop • As the flux rope decelerates, the displaced loop and shock escape from the driver • The shock escapes quickly after exiting the loop

  7. Dynamic spectrum • Assuming radio type II emission is produced at the leading edge of the shock, we plot frequency vs. time • Qualitative similarities

  8. Driven or blast wave? • In a simulation without dense loops, the shock also escapes from the flux rope Density Temperature • The skirt of the shock sweeps the solar surface followed by another wave • EIT waves?

  9. Summary of results • Depending on the variations of the Alfvén speed in the low corona, the erupting CME can at times acts as the driver of the shock, while at other times the shock may propagate freely • Difficult to determine whether coronal waves caused by flare or CME, low-cadence observations may be misleading • Correlation between speed and location of type II bursts and ejecta can be very complex • Possible that fragmented, high-frequency type IIs due to CME driven shocks propagating through dense coronal loops

  10. Conclusion • By performing numerical simulations side by side with analysis of observations, the physics involved in the coronal phenomena can more readily be extracted than by solely analyzing the observational data • All approaches needed in order to understand these dynamical processes

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