mhd modeling of coronal disturbances related to cme lift-off
DESCRIPTION
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. [email protected]. Introduction. - PowerPoint PPT PresentationTRANSCRIPT
MHD modeling of coronal disturbances related to
CME lift-off
J. Pomoell1, R. Vainio1, S. Pohjolainen2
1Department of Physics, University of Helsinki2Tuorla Observatory, University of Turku
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
Play a role in the acceleration of electrons and ions to high energies, exact mechanisms unclear
Observed in-situ and as various EM signatures
ST
ER
EO
AH
EA
D
EU
VI
195
ÅM
ay 1
9, 2
007
Type II radio bursts
Plasma emission (F+H) caused by shock-accelerated e-
, knowing gives
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)?
What about high-frequency type IIs?
(Pohjolainen, Pomoell, Vainio: A&A 490, 2008)
We address such issues by performing MHD simulations of CME lift-off
Look for features that might be of importance when interpreting observations
or ?
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
Eruption dynamics
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
Density Speed
Dynamic spectrum
Assuming radio type II emission is produced at the leading edge of the shock, we plot frequency vs. time
Qualitative similarities
Driven or blast wave?
In a simulation without dense loops, the shock also escapes from the flux rope
The skirt of the shock sweeps the solar surface followed by another wave
EIT waves?
Density Temperature
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
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