Geomagnetic activity and ionospheric absorption associated with high speed plasma streams

The ionospheric absorption can be rather enhanced at mid-latitudes after certain geomagnetic disturbances. The conditions for a post-storm event (PSE) in the lower ionosphere are regulated by magnetospheric processes which may also be influenced by changes in extraterrestrial parameters. Superposed epoch analysises have confirmed the appearance on three phases in the PSE associated with high speed plasma streams (HSPS), if the solar wind velocity maximum was above 600 km s-1. A rather significant PSE can occur in case of HSPS-events of higher peak velocities (V M > 600 km s-1) accompanied by solar flares. Furthermore, the efficiency of this connection also depends on the position of the flare on the visible solar disk. The main points detected on the basis of statistical analysis are also shown by a case study from the year 1978, i.e. outside of the originally investigated 1964-1975 interval