Dynamical and orbital properties of the Aricebo micrometeors

Using the Arecibo Observatory (AO) 430 MHz Radar we have developed a Doppler technique to measure very precise micrometeor instantaneous velocities directly from the meteor head-echo. In addition, a large number of these observations show deceleration. With the velocity, the deceleration, the assumption of a spherical shape, and a mean micrometeoroid mass density (3 g cm^{{combining triple dot above}}) we have obtained estimates of in-atmosphere particle sizes. Therefore we can produce a more realistic orbital analysis than previously obtained for micrometeors. We first use an MSIS standard atmosphere model and the measured deceleration in order to obtain the meteor extra-atmospheric speeds, assuming that sputtering is the only mass-loss mechanism that these particles undergo prior and during the time we detect them. So far, over 7000 detections obtained during the Leonids 1997 (L97) and 1200 during the Leonids 1998 (L98) observation campaigns have been analyzed. Out of these detections, we present elements without correction for perturbations (i.e. radiation pressure, perturbation by the Jovian planets and photoelectric charging effects) of over 500 events from 1997 and 200 from 1998.