5. Conclusion

[29]  As a result, we state that in 1974-1980, there was no PwD and that the UrEP activity was much less than in the period 1982-1992. The quantitative analysis of the PwDs confirmed our statement of the previous publications that in the case of UrEPs the middle atmosphere is abnormally ionized at altitudes between 20-40 km. The above estimation of an effective height h' of electric conductivity layer gives approximately 28-38 km.

[30]  According to the duration of the events the space range of the UrEPs was equal to some thousand km for some cases (along the auroral zone). In addition, it is necessary to note that there should exist two kinds of high-latitude absorption of the long and short radio waves: the first kind is provoked by solar cosmic rays (the protons), and the second kind is caused by UrEPs (when the riometers do not indicate on any disturbance). A sporadic ionized layer at the altitudes 20-50 km in the case of UrEPs should absorb the long and short radio waves like the ionospheric D layer does at daytime.