Outburst in activity of the 1986 Ursids reported from visual observations was observed also by the Budrio meteor radar. The radar maximum consisting mainly of long-duration echoes preceded the visual one by about half an hour. The peak appeared on December 22, 20∶49 UT (solar longitude 270°.202). The mean photographic orbit of the Ursids shower was derived and compared with that of the parent comet Tuttle.

Radar observations of the last bursts of the Leonids in 1969 and Lyrids in 1982, carried out at the Springhill Meteor Observatory, Canada, both of very short duration, with the rates exceeding a quarter-maximum rate within 50-55 minutes, are used for a study of the mass distribution of meteoroids. In both cases the mass distribution exponents of the meteoroids in the dense clouds largely differ from the values obtained for the older populations of the streams. The highest mass exponent s approximately 2.2-2.4 is found around the peak of the activity, confirming high contribution of smaller meteoroids, and thus also a recent origin of the dense clouds. Consequences of these findings are discussed.

Unusually long activity of the Taurid meteor complex, extending over 3-5 months according to new estimations based on various orbital similarity criteria, has been evoking controversies about the possible origin and dynamical evolution of this unique complex of meteor streams. It even casts doubts on the reality of the extension of the complex. In the present paper orbital elements and the extension of the Taurid meteor complex are re-examined on the bases of the most precise photographic meteor orbits available from the IAU Meteor Data Center in Lund. The results are evaluated and discussed from the viewpoint of various proposals on the origin and dynamical evolution of the complex.

Potential associations of Apollo asteroids with meteor streams are searched on the basis of the orbital parameters comparison. From all Apollo asteroids discovered through 1991 June those are only selected for further analysis whose orbits approach to less than 0.1 AU to the Earth's orbit. Their orbits are compared with precise photographic orbits of individual meteors from the Meteor Data Center in Lund. Results on the associations of asteroids with meteor streams are presented and discussed.

Radar data from long-enduring meteor trails observed during two different campaigns carried out at the CNR station in Budrio (45° N, 11° E) near Bologna in Autumn of 1980 and 1985 reveal that the wave field near the mesopause is composed of a superposition of wave motions to be connected possibly to propagating internal gravity waves. The measured vertical wavelengths ranged from 2 to 13 km with dominant wave activity at values between (2÷3) km and (6÷7) km. The observed small-scale wave activity suggests processes and effects of wave field saturation and of convective or dynamical instability.

A new observational method for determining winds on extremely small scales in the upper mesosphere has been developed by radar observations of relatively rare, but long enduring trails of bright meteors, known as fireballs. The radar meteor system near Bologna enables to determine wind velocities at the points on the fireball trail, separated from each other in a time scale of 1 s and in a distance scale by 0.1 km. Results of investigation of the fireballs observed in Bologna during the EBC (Energy Budget Campaign) in November 1980, based on the analysis of multiple or double reflections from meteor trails show the variation of the wind velocity in very small areas. Fireball trains can provide several independent echoes, connected with the position, orientation, total duration of the trail and with the efficiency of the radar equipment used. More complex information on the atmospheric irregularities and on their occurrence can be derived during the observations of meteor showers, analysing simultaneously the motion of the effective reflection point on the trail from the range drift of echoes, and the Doppler shift wind measurements.

Irregular wind motions in the meteor region ((70÷120) km) on very small space-time scales have been tentatively deduced by radar observations of relatively rare, but long enduring ionized trails of bright meteors (fireballs). The method here presented seems to be proper for the study of the turbulent winds in the upper mesosphere and lower thermosphere.