ИСТИНА

For investigation of the lower ionosphere during the period of an autumn equinox were used several facilities. For measurements by the partial reflection method it was used the facility in Tumanny (Murmansk oblast, Russia; 69.0N, 35.7E) with parameters: working frequencies - 2.652.72 MHz, transmitter pulse power - 60 kW, a pulse duration - 15 mks, sounding frequency – 2 Hz. The receiving-transmitting antenna had a square 105 m2 and a diagram 19x22. Signal amplitude registrations were implemented in the altitude range from 50 till 146 km with the measurement step of 1.5 km. For obtaining of electron content values a difference of absorption between ordinary and extraordinary waves was used. The digital vertical ionosonde (Geophysical Observatory Loparskaya, Murmansk oblast, Russia; 68.25N, 33.08E) had the working range of frequencies from 0.3 till 40 MHz which can be covered from several seconds till several minutes. A transmitter can generate pulses with the duration from 25 till 800 mks with repetition frequencies from 1 till 50 Hz and pulse power 15 kW. A transmitting antenna is a broadband delta-antenna with the height of 25 m and a receiving antenna is broadband antenna system with the height of 10 m. Ionospheric parameters can be received using standard methods. During of the period of observations in the observing points riometric and magnetic measurements were implemented. The observation of the polar lower ionosphere have shown that in the days of an autumn equinox there were a presence of intensive reflections from mesospheric layers at the altitudes 65–80 km. A distinctive feature of observed echoes is connection of the reflections with regions of lower electron density. During severe disturbances of the ionosphere which were accompanied with strong riometric absorption it was shown very high concentration of electron at the altitudes of 60 - 70 km. The observations permit to discuss possible mechanisms the effects including sufficient role of particles in ionization of the D region.