Micrometeor observations using the Arecibo 430 MHz radar I. Determination of the ballistic parameter from measured Doppler velocity and deceleration results

We present a sample of radar meteors detected during the November 1997 Leon ids shower period using the narrow-beam, high-power Arecibo Observatory 430 -MHz radar. During this period similar to 7700 events were detected over 73 h of observations that included six mornings. Near apex-crossing, 6-10 eve nts per minute were observed in the similar to 300-m diameter beam. From th ese events a total of 390 meteors are characterized by a clear linear decel eration as derived from the radial Doppler speed determined from the meteor -echo leading-edge (head-echo). We interpret our results in terms of the me teor ballistic parameter-the ratio of the meteoroid mass to cross-sectional area-yielding a physical characterization of these particles prior to any assumptions regarding meteoroid shape and mass density. In addition, we com pare these measurements with the results of a numerical solution of the met eor deceleration equation and find them in good agreement. The size and dyn amical mass of the meteoroids are estimated considering these particles to be spheres with densities of 3 g/cm(3). We also discuss atmospheric energy- loss mechanisms of these meteroids. We believe these are the first radar me teor decelerations detected since those ones reported by J. V. Evans (1966, J. Geophys, Res. 71, 171-188) and F. Verniani (1966, J. Geophys, Res, 71, 2749-2761; 1973, J. Geophys, Res, 78, 8429-8462) and the first ones for met eors of this size. (C) 2000 Academic Press.