5 Conclusions

From the presented relatively general estimations we find that the EIT-detected coronal transient waves and the type II exciting disturbances at larger coronal heights can well be different signatures of the same fast magnetosonic wave disturbance. The observed speed difference between the mean EIT transient wave and the mean type II burst signature follows quite naturally from the inhomogenity of the density and the magnetic field in the corona, and from the magnetic flux conservation law. The relationship between the measured speed of the EIT waves and the speed derived from type II drift rates is influenced by the heights at which both are excited, and the density structure of the corona. For this reason, the speed of the type II burst cannot simply be extrapolated from the measured EIT wave speed.

Bruzek ([1952], [1958]) and Yajima ([1971]) supposed that large flares can generate a slow wave disturbance which propagates at about the velocity of sound (this was inferred from the activation of distant filaments). The corresponding velocities are between 60-200 km s^-1. According to our opinion, the EIT coronal transient waves cannot be interpreted as simple acoustic waves. EIT waves are mainly propagating perpendicular to the magnetic field (what is impossible for slow magnetoacoustic waves, Priest [1982]), and they are related with density compressions (otherwise inobservable). Therefore, they are more compatible with a disturbance of fast mode nature. A more detailed analysis of the data is given by Mann et al. ([1999]).

Acknowledgements

The authors are thankful to the referee whose remarks essentially improved the paper. Further, the authors are grateful to the staff of the solar radio observatory of the Astrophysical Institute Potsdam. The extreme ultraviolet telescope (EIT) is one of the instruments onboard theSolar and Heliospheric Observatory (SOHO). SOHO is a joint NASA/ESA mission. The work of Andreas Klassen was paid by the Deutsche Forschungsgemeinschaft under grants DFG Au106/6-1 and Au106/6-2.