Solar Physics Seminar: Elena Khomenko (IAC, Spain)

What	seminar
When	20 March 08 from 04:00 pm to 05:00 pm
Where	Physics & Astrophysics Conf. Room 232
Add event to calendar	vCal (Windows, Linux) iCal (Mac OS X)

Numerical Simulations of Magneto-Acoustic Wave Propagation in Magnetic Structures of Different Size

In this talk, we present results of simulations of

magneto-acoustic waves from the photosphere to the chromosphere in

magnetic structures with different size. We compare the behaviour

of a thick flux tube with a size similar to a small sunspot with

the behaviour of a small-scale thin flux tube with a size typical

for the solar network elements. Both, thin and thick flux tubes in

our modeling posses an internal structure and have gradients of

the Alfven and Acoustic speeds in vertical and horizontal

directions. The waves are generated by a localized driver at the

photospheric level. In the case of the sunspot, the fast

(magnetic) mode in the region cS < vA does not reach the

chromosphere and reflects back to the photosphere at a somewhat

higher layer than the cS = vA line. This behavior is due to

wave refraction, caused, primarily, by the vertical and horizontal

gradients of the Alfven speed. The slow (acoustic) mode

continues up to the chromosphere along the magnetic field lines

with increasing amplitude. In the case of a network flux tube, the

photospheric driver moves the magnetic field lines in horizontal

direction exciting the slow (magnetic) mode. After the mode

transformation at heights above the temperature minimum, the

acoustic mode is produced. It follows straight up to the

chromosphere forming shocks. The direction of propagation of these

shocks is along the flux tube boundary. The main period observed in the

chromosphere depends on the radiative losses of oscillations.

The channeling of five-minute waves into the chromosphere is observed

in our simulations if the radiative relaxation time is sufficiently

small, as expected in small-scale magnetic structures as flux tubes.

July 2008

KIPAC