STRUCTURAL ASPECTS OF METEOROID STREAMS OBSERVED BY A FORWARD SCATTERRADAR SYSTEM

Forward scatter (FS) continuous wave (CW) meteor radar observations ca rried out during 1992-96 over;the long baseline Bologna-Lecce in Italy , enable us to investigate the structure of the main meteoroid I strea ms and of the sporadic background by the cumulative distributions vs d urations of the recorded echoes. The trends of the mass-distribution o f particles belonging to the quoted meteor complexes are discussed in terms of variations of the mass index s against echo durations and in terms of steady-state conditions for each meteor population. The mass index values of the sporadic background are generally higher than for meteor showers in the duration range of 0.1 less than or equal to T le ss than or equal to 10 s. Observational evidence indicates that the co mbined cumulative distributions of meteor trails vs peak signal amplit udes and vs durations represent a more sensitive indicator of the mete oroid stream activity, and consequently, of the mass-index variation. The unexpected high proportion of short-lived echoes which produce ver y faint meteors is interpreted in terms of fragmenting particles which form filaments younger than those present in other parts of the strea m. The effects of non-gravitational forces as the solar radiation pres sure,,the Poynting-Robertson (F-R) effect, mutual collisions, etc., ar e taken into account to justify the observed widespread radiants and u nstable populations of particles. (C) 1998 Elsevier Science Ltd. All r ights reserved.