MASS-DISTRIBUTION OF METEOROIDS OBTAINED BY A METEOR FORWARD-SCATTER (MFS) RADAR METHOD

The cumulative distributions of the number vs. duration of echoes belo nging to main meteor showers (Lyrids, eta-Aquarids, delta-Aquarids, Pe rseids, Orionids, Leonids, Geminids) and sporadic background were inve stigated using a forward-scatter (FS) continuous-wave (CW) meteor rada r link operational during 1992-95 over the long baseline Bologna-Lecce in Italy. The trend of the mass distribution of particles in the quot ed meteoroid streams was derived, and the values of the mass index s w ere compared for each meteor population with the steady-state conditio n (s < 11/6). It was found that the mass index s generally increases t owards long-duration echoes, but many of the observed meteor streams a ppear to have unstable populations. The values of the mass index of th e sporadic complex are generally higher (2.07 less than or equal to s less than or equal to 2.57) than the corresponding ones of meteor show ers in the range of echo durations 0.1 less than or equal to T less th an or equal to 10 s. This is a possible consequence of longer-lasting FS signals, indicating a shift of the mass distribution function vs. h igher echo durations. Moreover, non-gravitational forces in connection with solar radiation pressure, Poynting-Robertson effect, solar-wind particle streaming, mutual collisions, etc., appear to be responsible for the observed widespread radiants and for unstable populations in t he meteoroid streams.